U.S. patent application number 13/081821 was filed with the patent office on 2011-08-18 for semiconductor memory device suitable for mounting on a portable terminal.
This patent application is currently assigned to Renesas Technology Corp.. Invention is credited to Takeo Miki, Seiji Sawada, Masaki Tsukude.
Application Number | 20110199844 13/081821 |
Document ID | / |
Family ID | 34805858 |
Filed Date | 2011-08-18 |
United States Patent
Application |
20110199844 |
Kind Code |
A1 |
Miki; Takeo ; et
al. |
August 18, 2011 |
Semiconductor Memory Device Suitable for Mounting on a Portable
Terminal
Abstract
A semiconductor memory device for operating in synchronization
with a clock is disclosed. The semiconductor includes a memory
array having a plurality of memory cells arranged in rows and
columns; and a control circuit performing a control, operation to
effect row access processing on a selected row and to effect column
access processing on column(s). The control being performed in
synchronization with a first clock defined by a time of production
of the read signal or the write signal according to an externally
applied control signal. the control is also performed in
synchronization with a second or later clock defined by a latency,
to effect the column access processing on a second number of the
columns remaining in the burst mode access
Inventors: |
Miki; Takeo; (Hyogo, JP)
; Sawada; Seiji; (Hyogo, JP) ; Tsukude;
Masaki; (Hyogo, JP) |
Assignee: |
Renesas Technology Corp.
Tokyo
JP
|
Family ID: |
34805858 |
Appl. No.: |
13/081821 |
Filed: |
April 7, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12333913 |
Dec 12, 2008 |
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13081821 |
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12007032 |
Jan 4, 2008 |
7480200 |
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12333913 |
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11049059 |
Feb 3, 2005 |
7336557 |
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12007032 |
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Current U.S.
Class: |
365/193 ;
365/207; 365/233.1 |
Current CPC
Class: |
G11C 8/18 20130101; G11C
11/40615 20130101; G11C 2211/4061 20130101; G11C 11/406
20130101 |
Class at
Publication: |
365/193 ;
365/233.1; 365/207 |
International
Class: |
G11C 8/18 20060101
G11C008/18; G11C 7/06 20060101 G11C007/06 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 3, 2004 |
JP |
2004-026999 |
Claims
1. A semiconductor memory device for operating in synchronization
with a clock, performing access in a burst mode, and obtaining row
and column addresses prior to production of a read signal or a
write signal, comprising: a memory array having a plurality of
memory cells arranged in rows and columns; and a control circuit
performing control, in synchronization with a first clock defined
by a time of production of the read signal or the write signal
according to an externally applied control signal, to effect row
access processing on a selected row and to effect column access
processing on column(s) starting from a first position and being
equal in number to a first number exceeding zero and not exceeding
a burst length, and performing control, in synchronization with a
second or later clock defined by a latency, to effect the column
access processing on a second number of the columns remaining in
the burst mode access.
2. The semiconductor memory device according to claim 1, further
comprising: a sense amplifier circuit amplifying a potential on a
bit line pair connected to said memory cells; and a column decoder
selecting said column, wherein said control circuit includes: a
first control circuit producing a column enable signal in
accordance with a row activating signal being activated in
synchronization with said first clock according to timing following
production of a signal activating said sense amplifier, and a
second control circuit providing a first instructing signal
activating said first number of columns to said column decoder in
accordance with said column enable signal, and providing a second
instructing signal activating said second number of columns to said
column decoder in synchronization with said second clock or a later
clock.
3. The semiconductor memory device according to claim 2, wherein
said control circuit includes a circuit producing a signal
externally notifying of first timing data provided after column
access processing synchronized with said first clock.
4. The semiconductor memory device according to claim 2, wherein
said control circuit includes a circuit externally notifying of
timing of first data provided by performing column access
processing in synchronization with said second clock or the later
clock.
5. The semiconductor memory device according to claim 2, further
comprising: a shift circuit operating, as said first clock, a clock
immediately following end of execution of a refresh operation, a
read operation or a write operation when said read or write request
signal is produced during the execution of said refresh, read or
write operation.
6. A semiconductor memory device being set to one of a plurality of
operation modes according to a combination of external signals, and
comprising: a memory array having a plurality of memory cells
arranged in rows and columns; bit line pairs connected to the
memory cells; a first amplifier circuit amplifying a potential on
said bit line pair; an I/O line pair connected to said plurality of
bit line pairs; and two or more kinds of second amplifier circuits
being selectively activated in accordance with said mode for
amplifying the potential on said I/O line pair.
7. The semiconductor memory device according to claim 6, wherein
said plurality of operation modes include a synchronous operation
mode synchronous with an externally applied clock and an
asynchronous operation mode asynchronous to the clock; and said
second amplifier circuit includes: a first kind of amplifier
circuit corresponding to the synchronous operation mode, and a
second kind of amplifier circuit corresponding to the asynchronous
operation mode.
8. The semiconductor memory device according to claim 7, further
comprising: a control circuit setting said first and second kinds
of amplifier circuits to the active and inactive states,
respectively, when the synchronous mode is set, and setting said
first and second kinds of amplifier circuits to the inactive and
active states, respectively, when the asynchronous mode is set; and
a data bus driver connected to outputs of said first and second
kinds of amplifier circuits, and providing either an output of said
first kind of amplifier circuit or an output of said second kind of
amplifier circuit onto a data bus.
9. The semiconductor memory device according to claim 8, wherein
said first kind of amplifier circuit includes a switch unit
disconnecting said I/O line pair from an amplifier unit in said
first kind of amplifier circuit based on a signal synchronized with
the clock, and said second kind of amplifier does not include a
switch unit disconnecting said I/O line pair from an amplifier unit
in said second kind of amplifier circuit.
10. The semiconductor memory device according to claim 7, wherein
said first and second kinds of amplifier circuits connected to said
I/O line pair are aligned in a column direction, and said I/O line
pair is connected to said first and second kinds of amplifier
circuits without diverging.
11. A semiconductor memory device operable in synchronization with
a clock, comprising: a memory array having a plurality of memory
cells arranged in rows and columns; a byte mask control circuit
receiving an externally applied byte mask signal, and controlling
byte mask processing based on said byte mask signal; and an output
circuit receiving data provided from said memory cell, and not
outputting a byte corresponding to said byte mask signal of the
data provided from said memory cell, wherein when said byte mask
control circuit receives the externally applied byte mask signal
during row access processing performed for change to a second row
due to reaching a last column in a first row during an operation of
continuously effecting writing or reading on the first row and the
subsequent second row, said byte mask control circuit defers mask
processing to be effected on the byte corresponding to said byte
mask signal until data of a next bit is output after the end of
said row access.
12. The semiconductor memory device according to claim 11, further
comprising: a wait control circuit outputting a wait signal
externally notifying that waiting is performed until output of data
while the row access processing is being performed for the change
to the next row; said byte mask control circuit includes, for each
byte: a first circuit providing a signal produced based on said
byte mask signal without disabling an output enable signal
corresponding to said byte in such a case that said byte mask
signal indicates that the byte mask is to be effected on the bit
other than the leading bit to be subjected to said continuous
reading or writing, and particularly in such a case that said wait
signal is issued according to timing of output of said bit from
said output circuit while the row access processing for change to
said next row is not to be performed, and a second circuit
receiving and holding a signal produced based on said byte mask
signal for disabling the output enable signal corresponding to said
byte according to timing of releasing of said wait signal; and when
said output enable signal indicates "disable", said output circuit
does not provide the byte, corresponding to said output enable
signal indicating the "disable", of the data provided from said
memory cell.
13. A semiconductor memory device having a synchronous mode for
operation synchronous with a clock and an asynchronous mode for
operation asynchronous to the clock, comprising: a memory array
having a plurality of memory cells arranged in rows and columns; a
setting circuit capable of setting one of a synchronous-fixed mode,
an asynchronous-fixed mode and a synchronous/asynchronous mixed
mode; an asynchronous-changing circuit determining in said mixed
mode whether a time from asserting of an external chip enable
signal to rising of an external clock is equal to or greater than a
predetermined value or not, and changing the mode to the
asynchronous-fixed mode when the time is equal to or greater than
said predetermined value; a synchronous control circuit controlling
a synchronous operation when the synchronous-fixed mode or the
mixed mode is set; and an asynchronous control circuit controlling
the asynchronous operation when the asynchronous-fixed mode or the
mixed mode is set, or when the mode is changed to the
asynchronous-fixed mode, wherein said asynchronous-changing circuit
is deactivated in accordance with an output of the setting
circuit.
14. The semiconductor memory device according to claim 13, wherein
said setting circuit is predetermined two bits in a bus
configuration register, and said asynchronous-changing circuit
stops processing for said changing when a value of said bits
indicates the synchronous-fixed mode and the asynchronous-fixed
mode.
15. A semiconductor memory device operable in synchronization with
a clock comprising: a memory array having a plurality of memory
cells arranged in rows and columns; a chip enable buffer receiving
an external chip enable signal, and producing an internal chip
enable signal; a clock buffer receiving an external clock and
producing an internal clock; an address buffer receiving an
external address signal and producing an internal address signal;
and a control buffer receiving an external control signal other
than the external chip enable signal and producing an internal
control signal, wherein said clock buffer, said address buffer and
said control buffer receive said internal chip enable signal, and
stop operations when said internal chip enable signal indicates
deactivation of the chip; said clock buffer, said address buffer
and said control buffer execute the operations when said internal
chip enable signal indicates activation; said control buffer
receives an external address take-in signal, and produces an
internal address take-in signal; said semiconductor memory device
further comprising: a delay circuit delaying said internal address
take-in signal by a predetermined delay amount, a data holding
circuit holding an output of said delay circuit in synchronization
with the internal clock; a logical circuit providing an AND signal
obtained from an output of said data holding circuit and said
internal clock; a circuit activating a row address strobe signal
based on a leading pulse of said AND signal; and said predetermined
delay amount of said delay circuit is determined such that the
leading pulse of said AND signal is formed of an internal clock
pulse produced from an external clock pulse rising during an active
state of said external address take-in signal.
16. A semiconductor memory device being set to one of a plurality
of operation modes, the semiconductor memory device comprising: a
memory array having a plurality of memory cells arranged in rows
and columns; bit line pairs connected to the memory cells; a first
amplifier circuit amplifying a potential on said bit line pair; an
I/O line pair connected to said plurality of bit line pairs; and
two or more different types of second amplifier circuits connected
to said I/O line pair and aligned in a column direction and wherein
said I/O line pair connects said two or more different types of
second amplifier circuits to one another.
17. The semiconductor memory device according to claim 16, wherein
a first type of second amplifier is arranged in a first region and
a second type of second amplifier is arranged in a second
region.
18. The semiconductor memory device according to claim 16, wherein
a first type of second amplifier circuit is a
synchronous-compatible preamplifier and a second type of second
amplifier is an asynchronous-compatible preamplifier.
19. The semiconductor memory device according to claim 16, wherein
said two or more different types of second amplifier circuits are
serially connected via said I/O line pair.
20. A semiconductor memory device being set to one a plurality of
operation modes said semiconductor memory device comprising: a
memory array having a plurality of memory cells arranged in rows
and columns; bit line pairs connected to memory cells; a first
amplifier circuit amplifying a potential on said bit line pair; an
I/O line pair connected to said plurality of bit line pairs; two or
more different types of second amplifier circuits connected to each
I/O line pair and aligned in a row direction.
21. The semiconductor memory device according to claim 20, wherein
said I/O line pair has divergent portions which are connected to
said two or more different types of second amplifier circuits,
respectively.
22. The semiconductor memory device according to claim 20, wherein
a first type of second amplifier circuit is a
synchronous-compatible preamplifier and a second type of second
amplifier circuit is an asynchronous-compatible preamplifier.
23. The semiconductor memory device according to claim 20, wherein
said two or more different types of second amplifier circuits are
arranged in a synchronous/asynchronous-compatible preamplifier
arrangement region.
Description
RELATED APPLICATION
[0001] This application is a divisional of U.S. application Ser.
No. 12/333,913, which is a divisional of U.S. application Ser. No.
11/049,059, now U.S. Pat. No. 7,336,557, the contents of which are
herein incorporated in their entirety by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a semiconductor memory
device, and particularly to a semiconductor memory device suitable
for mounting on a portable terminal.
[0004] 2. Description of the Background Art
[0005] Semiconductor memory devices, which are used in portable
terminals such as cellular phones, employ pseudo-SRAMs (Static
Random Access Memories) for achieving large capacities and easy
control. The pseudo-SRAM includes DRAM (Dynamic Random Access
Memory) cells as internal memory cells, and also includes an
interface, which is asynchronous to a clock similar to that of a
SRAM, as an external interface for defining input control signals
and address signals. A refresh operation is not controlled by an
externally applied signal, but is performed internally and
automatically (e.g., see Japanese Patent Laying-Open No.
2002-352577).
[0006] For further achieving a high speed operation, a synchronous
pseudo-SRAM, which additionally employs a synchronous interface,
has been available, e.g., as CellularRAM.RTM. disclosed on the
Internet Web site (URL:
http://www.micron.com/products/psram/cellularram/). This
synchronous pseudo-SRAM includes a synchronous interface
synchronized with a clock similar to that of a SRAM in addition to
an asynchronous interface not synchronized with the clock.
[0007] According to the synchronous pseudo-SRAM, a WAIT signal is
issued to notify that external access is prohibited, before
elapsing of a command latency CL, which is the number of clocks
issued until data is output after reception of a read or write
request, and while self-refresh is being performed. In a
conventional structure, command latency CL is externally applied.
However, the synchronous pseudo-SRAM does not require such external
application because the WAIT signal can be internally issued to
notify that the access is impossible. Command latency CL of a more
appropriate value can be determined by internally determining it
within the synchronous pseudo-SRAM according to a current state, as
compared with the case of externally determining the command
latency.
[0008] In contrast to the above, Japanese Patent Laying-Open No.
2001-155484 has disclosed a latency determining circuit, which can
adjust a latency according to a clock frequency. This latency
determining circuit includes a latency determining instruction
input unit, which issues an internal start signal in response to
activation of a latency determination start signal for starting
latency determination in synchronization with a clock signal, a
latency section defining circuit, which issues a predetermined
latency determination section signal at every edge of the clock
signal in response to the latency determination start signal, a
delay unit issuing a delay signal to adjust the latency by delaying
the internal start signal by a predetermined time, and a latency
instructing circuit, which determines a latency number in response
to the latency determination start signal and the latency
determination section signal at the point in time of activation of
the delay signal. The latency determining circuit described above
can internally determine the latency without an external
instruction.
[0009] For example, Japanese Patent Laying-Open No. 07-226077 has
disclosed a method, in which self-refresh is performed
simultaneously with reading or writing in the case where a
pseudo-SRAM has multiple banks. More specifically, according to the
paragraph [0020] in Japanese Patent Laying-Open No. 07-226077, even
when one of first to fourth cell banks 10-13 is in a refresh mode,
first to fourth row address latch circuits and buffers 80-83 can
transmit second load address signals A.sub.0-A.sub.n-2 latched by a
row address latch circuit 70 to remaining three cell banks to allow
access to data even during the refresh mode.
[0010] However, the following problems arise in the methods
disclosed in the foregoing references.
[0011] Although Japanese Patent Laying-Open No. 2001-155484 has
disclosed a manner of internally setting the latency, it has not
disclosed timing for setting the latency.
[0012] Although Japanese Patent Laying-Open No. 07-226077 has
disclosed a manner of performing the refresh simultaneously with
reading or writing when the bank to be refreshed is different from
the bank of a reading or writing target, it has not disclosed a
manner of determining the bank to be refreshed such that the bank
to be refreshed may not overlap with the bank of the reading or
writing target.
[0013] Further, in a structure having a plurality of pseudo-SRAMs
accommodated in a single package, each pseudo-SRAM performs the
refreshing according to timing different from the timing of the
others. This results in a conflict of the WAIT signals issued from
the respective pseudo-SRAMs.
[0014] Further, there is such a problem that data cannot be output
according to timing earlier than the timing defined by command
latency CL.
[0015] In the case where the pseudo-SRAM has multiple modes such as
a synchronous mode and an asynchronous mode, and operates in one
mode selected from these modes, a preamplifier, which can operate
appropriately in a certain mode, may not operate appropriately in
another mode, and thus may not correctly perform amplification.
[0016] In the case where a processing target changes to a next row
during continuous reading or writing, a byte mask signal must be
applied after an externally applied WAIT signal notifies of the
completion of processing for starting processing of a next row
(i.e., deactivation of a word line in the last processed row,
activation of a word line in the next target row, amplification by
a sense amplifier and others).
[0017] For precharging a bit line pair, a chip enable signal must
be externally deactivated, and thus external control is
required.
[0018] Semiconductor memory devices such as a CellularRAM.RTM.
cannot operate synchronously with a clock of a low frequency.
[0019] When a chip is on standby, or is inactive because another
chip is being accessed, an input/output buffer continues an
operation, and thus wastes a current.
SUMMARY OF THE INVENTION
[0020] Accordingly, an object of the invention is to provide a
semiconductor memory device, which internally sets a latency
according to appropriate timing.
[0021] Another object of the invention is to provide a
semiconductor memory device, which appropriately determines a bank
to be refreshed while preventing overlapping of the bank to be
refreshed with a bank of a reading or writing target.
[0022] Still another object of the invention is to provide a
semiconductor memory device, which has a plurality of pseudo-SRAMs
arranged within a single package, and can refresh them according to
the same timing.
[0023] Yet another object of the invention is to provide a
semiconductor memory device, which can output data according to
timing earlier than timing defined by command latency CL.
[0024] Further another object of the invention is to provide a
semiconductor memory device, which has multiple modes, and can
appropriately operate a preamplifier in all the modes when one of
the modes is selected for operation.
[0025] A further object of the invention is to provide a
semiconductor memory device, in which a byte mask signal can be
externally applied similarly to the case of not moving to a next
row even when change to the new row is to be performed during
continuous reading or writing.
[0026] A further object of the invention is to provide a
semiconductor memory device, which can precharge a bit line pair
only under internal control without requiring external control.
[0027] A further object of the invention is to provide a
semiconductor memory device, which can operate in a synchronous
manner with a clock of a low frequency.
[0028] A further object of the invention is to provide a
semiconductor memory device, which can prevent such a situation
that an input/output buffer continues an operation in an inactive
chip, and thereby wastes a current.
[0029] According to an aspect of the invention, a semiconductor
memory device operable in synchronization with a clock includes a
memory array having a plurality of memory cells arranged in rows
and columns; a trigger producing circuit providing a trigger
signal; a delay circuit receiving the trigger signal, and providing
a delay signal produced by delaying the trigger signal; a clock
counter receiving the clocks, counting the received clocks during a
period from reception of the trigger signal to reception of the
delay signal, and providing a result of the counting; a determining
circuit storing a relationship between the number of clocks and a
latency, and determining the latency corresponding to the result of
counting provided from the clock counter; a register holding the
determined latency; and a wait control circuit externally providing
a wait signal based on the latency held in the register.
[0030] According to another aspect of the invention, a
semiconductor memory device includes a memory array having memory
cells of a plurality of dynamic random access memories arranged in
rows and columns, and having a plurality of banks each forming a
unit to be refreshed at a time; a circuit providing a trigger of
refreshing; a bank select circuit selecting the bank different from
the currently operating bank, and providing an address of the
selected bank when the currently operating bank is performing an
externally instructed operation at the time of reception of the
refresh trigger; and a refresh control circuit refreshing the bank
at the received address. The bank select circuit includes a
register holding addresses of the refreshed banks, and erasing all
the addresses held in the register when the addresses of all the
banks are held, a determining circuit determining the addresses of
the unrefreshed banks by referring to the register when the refresh
trigger is received, and a comparing circuit comparing the address
of the unrefreshed bank with the address of the currently operating
bank, and providing the address of the unrefreshed bank when the
address of the unrefreshed bank is different from the address of
the currently operating bank.
[0031] According to still another aspect of the invention, a
semiconductor memory device includes a memory array having memory
cells of a plurality of dynamic random access memories arranged in
rows and columns; a first circuit producing a first signal defining
timing of refreshing; an output terminal outputting the first
signal; an input terminal receiving a second signal externally
defining the timing of the refreshing; a switch receiving the first
and second signals, and outputting one of the first and second
signals; and a second circuit receiving the signal output from the
switch, and performing refresh control based on the received
signal.
[0032] According to further another aspect of the invention, a
semiconductor memory device for operating in synchronization with a
clock, performing access in a burst mode, and obtaining row and
column addresses prior to production of a read signal or a write
signal, includes a memory array having a plurality of memory cells
arranged in rows and columns; and a control circuit performing
control, in synchronization with a first clock defined by a time of
production of the read signal or the write signal according to an
externally applied control signal, to effect row access processing
on a selected row and to effect column access processing on
column(s) starting from a first position and being equal in number
to a first number exceeding zero and not exceeding a burst length,
and performing control, in synchronization with a second or later
clock defined by a latency, to effect the column access processing
on a second number of the columns remaining in the burst mode
access.
[0033] According to further another aspect of the invention, a
semiconductor memory device being set to one of a plurality of
operation modes according to a combination of external signals,
includes a memory array having a plurality of memory cells arranged
in rows and columns; bit line pairs connected to the memory cells;
a first amplifier circuit amplifying a potential on the bit line
pair; an I/O line pair connected to the plurality of bit line
pairs; and two or more kinds of second amplifier circuits being
selectively activated in accordance with the mode for amplifying
the potential on the I/O line pair.
[0034] According to further another aspect of the invention, a
semiconductor memory device operable in synchronization with a
clock includes a memory array having a plurality of memory cells
arranged in rows and columns; a byte mask control circuit receiving
an externally applied byte mask signal, and controlling byte mask
processing based on the byte mask signal; and an output circuit
receiving data provided from the memory cell, and not outputting a
byte corresponding to the byte mask signal of the data provided
from the memory cell. When the byte mask control circuit receives
the externally applied byte mask signal during row access
processing performed for change to a second row due to reaching a
last column in a first row during an operation of continuously
effecting writing or reading on the first row and the subsequent
second row, the byte mask control circuit defers mask processing to
be effected on the byte corresponding to the byte mask signal until
data of a next bit is output after the end of the row access.
[0035] According to further another aspect of the invention, a
semiconductor memory device having a synchronous mode for operation
synchronous with a clock and an asynchronous mode for operation
asynchronous to the clock, includes a memory array having a
plurality of memory cells arranged in rows and columns; a setting
circuit capable of setting one of a synchronous-fixed mode, an
asynchronous-fixed mode and a synchronous/asynchronous mixed mode;
an asynchronous-changing circuit determining in the mixed mode
whether a time from asserting of an external chip enable signal to
rising of an external clock is equal to or greater than a
predetermined value or not, and changing the mode to the
asynchronous-fixed mode when the time is equal to or greater than
the predetermined value; a synchronous control circuit controlling
a synchronous operation when the synchronous-fixed mode or the
mixed mode is set; and an asynchronous control circuit controlling
the asynchronous operation when the asynchronous-fixed mode or the
mixed mode is set, or when the mode is changed to the
asynchronous-fixed mode. The asynchronous-changing circuit is
deactivated in accordance with an output of the setting
circuit.
[0036] According to further another aspect of the invention, a
semiconductor memory device operable in synchronization with a
clock includes a memory array having a plurality of memory cells
arranged in rows and columns; a chip enable buffer receiving an
external chip enable signal, and producing an internal chip enable
signal; a clock buffer receiving an external clock and producing an
internal clock; an address buffer receiving an external address
signal and producing an internal address signal; and a control
buffer receiving an external control signal other than the external
chip enable signal and producing an internal control signal. The
clock buffer, the address buffer and the control buffer receive the
internal chip enable signal, and stop operations when the internal
chip enable signal indicates deactivation of the chip. The clock
buffer, the address buffer and the control buffer execute the
operations when the internal chip enable signal indicates
activation. The control buffer receives an external address take-in
signal, and produces an internal address take-in signal. The
semiconductor memory device further includes a delay circuit
delaying the internal address take-in signal by a predetermined
delay amount; a data holding circuit holding an output of the delay
circuit in synchronization with the internal clock; a logical
circuit providing an AND signal obtained from an output of the data
holding circuit and the internal clock; and a circuit activating a
row address strobe signal based on a leading pulse of the AND
signal. The predetermined delay amount of the delay circuit is
determined such that the leading pulse of the AND signal is formed
of an internal clock pulse produced from an external clock pulse
rising during an active state of the external address take-in
signal.
[0037] According to further another aspect of the invention, a
semiconductor memory device being set to one of a plurality of
operation modes, the semiconductor memory device includes a memory
array having a plurality of memory cells arranged in rows and
columns; bit line pairs connected to the memory cells a first
amplifier circuit amplifying a potential on bit line pair; an I/O
line pair connected to plurality of bit line pairs; and two or more
different types of second amplifier circuits connected to I/O line
pair and aligned in a column direction and wherein I/O line pair
connects two or more different types of second amplifier circuits
to one another.
[0038] According to further another aspect of the invention, a
semiconductor memory device being set to one a plurality of
operation modes semiconductor memory device includes a memory array
having a plurality of memory cells arranged in rows and columns;
bit line pairs connected to memory cells; a first amplifier circuit
amplifying a potential on bit line pair; an I/O line pair connected
to plurality of bit line pairs; two or more different types of
second amplifier circuits connected to each I/O line pair and
aligned in a row direction.
[0039] The semiconductor memory device according to the above
aspect of the invention can internally set the latency according to
appropriate timing.
[0040] Also, the semiconductor memory device according to the above
aspect of the invention can appropriately determine the bank to be
refreshed without causing overlapping with the bank of the read or
write target.
[0041] Further, the semiconductor memory device according to the
above aspect of the invention allows refreshing of a plurality of
pseudo-SRAMs arranged in one package according to the same
timing.
[0042] Further, the semiconductor memory device according to the
above aspect of the invention can output the data according to the
timing earlier than the timing defined by the command latency.
[0043] Further, according to the above aspect of the invention, if
the semiconductor memory device has the plurality of modes, and is
configured to operate by selecting one of the modes, the
preamplifier can operate appropriately in all the modes.
[0044] Further, according to the above aspect of the invention,
when the processing target changes to the next row while the
reading or writing is being continuously performed in the
semiconductor memory device, the byte mask signal can be externally
applied similarly to the case of not changing to the next row.
[0045] Further, the semiconductor memory device according to the
above aspect of the invention can precharge the bit line pair only
under the internal control without requiring external control.
[0046] Further, the semiconductor memory device according to the
above aspect of the invention can operate with a clock of a low
frequency and in a synchronous manner.
[0047] Further, the semiconductor memory device according to the
above aspect of the invention can prevent such a situation that an
I/O buffer continues an operation in an inactive chip, and thereby
wastes a current.
[0048] The foregoing and other objects, features, aspects and
advantages of the present invention will become more apparent from
the following detailed description of the present invention when
taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0049] FIG. 1 shows a structure of a synchronous pseudo-SRAM 100
according to a first embodiment.
[0050] FIG. 2 shows a specific structure of a trigger producing
circuit 104.
[0051] FIG. 3 is a timing chart of signals produced by trigger
producing circuit 104.
[0052] FIG. 4 shows a structure of a synchronous pseudo-SRAM 200
according to a second embodiment.
[0053] FIG. 5 shows a specific structure of a refresh bank address
designating circuit 213.
[0054] FIG. 6 illustrates an operation of a synchronous pseudo-SRAM
of a background art.
[0055] FIG. 7 illustrates an example of an operation of a
synchronous pseudo-SRAM 200 according to a second embodiment.
[0056] FIG. 8 illustrates another example of the operation of
synchronous pseudo-SRAM 200.
[0057] FIG. 9 shows a structure of one of synchronous pseudo-SRAMs
300 accommodated in one package according to a third
embodiment.
[0058] FIG. 10 shows a specific structure of a refresh control
circuit 305.
[0059] FIG. 11 shows a structure of a package accommodating two
synchronous pseudo-SRAMs according to the third embodiment.
[0060] FIG. 12 shows a structure of a synchronous pseudo-SRAM 400
according to a fourth embodiment.
[0061] FIG. 13 shows a structure of a row control circuit 409.
[0062] FIG. 14 shows a structure of a column control circuit
407.
[0063] FIG. 15 shows a specific structure of a CDETRG generating
circuit 421.
[0064] FIG. 16 shows a structure of a WAIT control circuit 412.
[0065] FIG. 17 illustrates timing of a WAIT signal of a synchronous
pseudo-SRAM in a background art.
[0066] FIG. 18 illustrates timing of a WAIT_ASYN signal and a WAIT
signal of synchronous pseudo-SRAM 400 according to a fourth
embodiment.
[0067] FIG. 19 shows a structure of a column decoder 417.
[0068] FIG. 20 is a timing chart illustrating an operation of
synchronous pseudo-SRAM according to the fourth embodiment.
[0069] FIG. 21 shows a structure of a row control circuit 499.
[0070] FIG. 22 illustrates input and output signals of a command
shift circuit 480.
[0071] FIG. 23 shows a specific structure of command shift circuit
480.
[0072] FIG. 24A illustrates a corrected read signal READF appearing
when a read signal READ is input while a refresh operation is not
being performed, and FIG. 24B illustrates corrected read signal
READF appearing when read signal READ is input during the refresh
operation.
[0073] FIG. 25 shows a structure of a synchronous pseudo-SRAM 500
according to a fifth embodiment.
[0074] FIG. 26 shows a structure of a shared signal producing
circuit 507.
[0075] FIG. 27A is a timing chart illustrating production of a
synchronization instructing signal SYNC in the case where an
external clock CLK is input, and FIG. 27B is a timing chart
illustrating production of synchronization instructing signal SYNC
in the case where external clock CLK is not input.
[0076] FIG. 28 shows a structure of a synchronous-compatible
preamplifier control circuit 508.
[0077] FIG. 29 shows a structure of a reference signal generator
521.
[0078] FIG. 30 shows an example of a High-side Delay.
[0079] FIG. 31 shows a structure of a synchronous-compatible
preamplifier control signal generator 522.
[0080] FIG. 32 illustrates timing of production of signals related
to a synchronous-compatible preamplifier 512.
[0081] FIG. 33 shows a structure of an asynchronous-compatible
preamplifier control circuit 509.
[0082] FIG. 34 showing timing of production of signals related to
an asynchronous-compatible preamplifier 513.
[0083] FIG. 35 shows a structure of synchronous-compatible
preamplifier 512.
[0084] FIG. 36 is a diagram illustrating that
synchronous-compatible preamplifier 512 is not suitable for
asynchronous reading.
[0085] FIG. 37 shows a structure of asynchronous-compatible
preamplifier 513.
[0086] FIG. 38 illustrates changes on potentials on nodes of
asynchronous-compatible personal computer 513 over time.
[0087] FIG. 39 shows a structure of a synchronous-compatible DB
driver 514.
[0088] FIG. 40 shows a structure of an asynchronous-compatible DB
driver 516.
[0089] FIG. 41 shows a structure of a shared DB driver 590 serving
as synchronous- and asynchronous compatible DB drivers 514 and
515.
[0090] FIG. 42 shows an arrangement of synchronous- and
asynchronous-compatible preamplifiers 512 and 513.
[0091] FIG. 43 shows another arrangement of synchronous- and
asynchronous-compatible preamplifiers 512 and 513.
[0092] FIG. 44 shows a structure of a synchronous pseudo-SRAM 600
according to a sixth embodiment.
[0093] FIG. 45 shows a specific structure of a CE buffer 609.
[0094] FIG. 46 shows a specific structure of a UB buffer 605.
[0095] FIG. 47 shows a specific structure of a ZUB0 producing
circuit 613.
[0096] FIG. 48 shows a specific structure of a ZLB0 producing
circuit 614.
[0097] FIG. 49 shows a specific structure of an ADV0 producing
circuit 615.
[0098] FIG. 50 shows a specific structure of a ZWE0 producing
circuit 616.
[0099] FIG. 51 shows a specific structure of a ZRST producing
circuit 612.
[0100] FIG. 52 illustrates timing of production of a ZRST.
[0101] FIG. 53 shows a specific structure of a mask control circuit
617.
[0102] FIG. 54 is a timing chart illustrating changes of signals
occurring in the case where change to a next row is not performed
during a burst read operation in synchronous pseudo-SRAM 600
according to the sixth embodiment.
[0103] FIG. 55 is a timing chart illustrating changes of signals
occurring in the case where change to a next row is performed
during the burst read operation when synchronous pseudo-SRAM 600
according to the sixth embodiment is in a no-wrap mode.
[0104] FIG. 56 shows a structure of a RAM 700 according to a
seventh embodiment.
[0105] FIG. 57 illustrates a structure of a shared unit 702.
[0106] FIG. 58 illustrates a structure of a cellular RAM dedicated
unit 704.
[0107] FIG. 59 illustrates a structure of a mobile RAM dedicated
unit 703.
[0108] FIG. 60 shows a structure of a synchronous pseudo-SRAM 800
according to an eighth embodiment.
[0109] FIG. 61 shows a specific structure of a burst length counter
805.
[0110] FIG. 62 is a timing chart illustrating deactivation of word
lines.
[0111] FIG. 63 illustrates a manner of setting synchronous and
asynchronous modes in the background art.
[0112] FIG. 64A illustrates mode setting with tCSP equal to 7.5 ns,
and FIG. 64B illustrates mode setting with tCSP equal to 22.5
ns.
[0113] FIG. 65 illustrates a manner of setting synchronous and
asynchronous modes in a ninth embodiment.
[0114] FIG. 66 shows a structure of a synchronous pseudo-SRAM 900
according to the ninth embodiment.
[0115] FIG. 67 shows a structure of a synchronous pseudo-SRAM 1000
according to a tenth embodiment.
[0116] FIG. 68 shows a structure of an ADV0 generating circuit 1050
in the background art.
[0117] FIG. 69 illustrates timing of changes occurring in various
signals when ADV0 generating circuit 1050 in the background art is
used.
[0118] FIG. 70 shows a structure of an ADV0 generating circuit 1010
in the tenth embodiment.
[0119] FIG. 71 illustrates timing of changes occurring in various
signals when ADV0 generating circuit 1010 in the tenth embodiment
is used.
[0120] FIG. 72 illustrates timing of precharging delayed when an
external chip enable signal CE# asynchronously becomes
inactive.
[0121] FIG. 73 shows another example of a data holding circuit.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0122] Embodiments of the invention will now be described with
reference to the drawings.
First Embodiment
[0123] A first embodiment relates to a synchronous pseudo-SRAM,
which can internally and automatically set a latency to an
appropriate value according to appropriate timing.
[0124] (Structure)
[0125] FIG. 1 shows a structure of synchronous pseudo-SRAM 100
according to the first embodiment. Referring to FIG. 1, synchronous
pseudo-SRAM 100 includes a DRAM cell array and peripheral circuit
group 101, an address buffer 103 and a control circuit 102.
[0126] A DRAM cell array in DRAM cell array and peripheral circuit
group 101 is a memory array formed of cells of a Dynamic Random
Access Memory (DRAM). Peripheral circuit group 101 includes a
global I/O line pair GIOP (GIO and /GIO), column select lines
provided corresponding to respective columns, column select gates,
sense amplifiers, preamplifiers, a write driver, a row decoder, a
column decoder and others.
[0127] Address buffer 103 receives an external address signal
ADD[21:0], and produces an internal address signal.
[0128] Control circuit 102 includes a trigger producing circuit
104, a counter enable circuit 105, a clock counter 106, a
determining circuit 107, a latency register 108 (i.e., a register
for a latency), a WAIT control circuit 109, a delay circuit 110 and
a refresh control circuit 111.
[0129] Refresh control circuit 111 controls a self-refresh
operation of the DRAM cell array based on an internal refresh timer
(not shown).
[0130] Trigger producing circuit 104 outputs a trigger signal
Trigger, which triggers setting of a latency.
[0131] Delay circuit 110 is formed of a plurality of inverters.
Delay circuit 110 receives trigger signal Trigger, and provides a
delayed trigger signal dTrigger.
[0132] Counter enable circuit 105 keeps a counter enable signal CE
at "H" for a period from reception of trigger signal Trigger to
reception of delayed trigger signal dTrigger.
[0133] Clock counter 106 counts external clocks CLK applied thereto
while counter enable signal CE is at "H". The count depends on the
number of applied external clocks CLK and a period of the "H" state
of counter enable signal CE, i.e., the delay amount, by which delay
circuit 110 delays trigger signal Trigger. The delay amount of
delay circuit 110 depends on ambient environments such as a
temperature.
[0134] Determining circuit 107 stores a relationship between the
count of clocks and the minimum latency allowing the operation with
the count. This relationship is determined such that the minimum
latency increases with increase in count of the clocks. Based on
this relationship, determining circuit 107 determines the minimum
latency corresponding to the count provided from clock counter 106,
and provides it to latency register 108.
[0135] Latency register 108 holds the minimum latency sent from
determining circuit 107.
[0136] WAIT control circuit 109 keeps the WAIT signal at "L" only
for a period corresponding to the minimum latency held in latency
register 108.
[0137] FIG. 2 shows a specific structure of trigger producing
circuit 104. In FIG. 2, trigger producing circuit 104 is formed of
a latch circuit 121, inverters IV1, IV2 and IV3, and an AND circuit
AND1.
[0138] FIG. 3 is a timing chart of signals produced by trigger
producing circuit 104. Referring to FIG. 3, latch circuit 121
latches an external address take-in signal ADV#, and provides an
address take-in latch signal ADV#L. Latch circuit 121 latches an
external chip enable signal CE#, and provides a chip enable latch
signal CE#L. Latch circuit 121 latches an external write enable
signal WE#, and provides a write enable latch signal WE#L. Latch
circuit 121 latches an external configuration register enable
signal CRE#, and provides a configuration register enable latch
signal CREL. AND circuit AND1 activates a read signal READ to
attain "H", and sets trigger signal Trigger to "H" when address
take-in latch signal ADV#L is at "L", chip enable latch signal CE#L
is at "L", write enable latch signal WE#L is at "H", configuration
register enable latch signal CREL is at "L" and external clock CLK
is at "H".
[0139] When trigger producing circuit 104 described above produces
read signal READ for performing the reading according to a
combination of logical values of the external signals, trigger
signal Trigger is also produced, and the latency is set.
[0140] According to the synchronous pseudo-SRAM of the embodiment
of this embodiment, as described above, when read signal READ is
produced and the command latency for read processing is actually
required, the latency can be set to a minimum value allowing an
operation with a frequency of applied external clock CLK and under
ambient environments such as a temperature.
[0141] According to this embodiment, delay circuit 110 is formed of
the plurality of inverters. However, delay circuit 110 is not
restricted to such a structure, and may be formed of, e.g., a
replica circuit reproducing a specific fashion in an imitating
fashion. Clock counter 106 may be configured to receive the
internal clock instead of external clock CLK.
[0142] This embodiment is not restrictively applied to the
synchronous pseudo-SRAM, and may be applied to various
semiconductor memory devices operating in synchronization with
clocks.
Modification of First Embodiment
[0143] According to the first embodiment, trigger producing circuit
104 detects the production of read signal READ, and thereby
produces trigger signal Trigger. However, this is not restrictive.
For example, trigger signal Trigger may be produced as follows.
[0144] (1) Trigger signal Trigger is produced by detecting input of
another operation instructing signal such as a write signal
WRITE.
[0145] (2) Trigger signal Trigger is produced when a power-on
detecting circuit detects the turn-on.
[0146] (3) Trigger signal Trigger is produced when an operation
mode setting command determining circuit determines that mode
setting relating to, e.g., a latency and a burst length is set
according to external signals.
[0147] (4) Trigger signal Trigger is produced when a temperature
change detecting circuit detects a change in temperature.
[0148] (5) An internal signal producing circuit produces trigger
signal Trigger at constant intervals.
Second Embodiment
[0149] A second embodiment relates to synchronous pseudo-SRAM, in
which a WAIT period is reduced by appropriately changing banks to
be self-refreshed.
[0150] (Structure)
[0151] FIG. 4 shows a structure of a synchronous pseudo-SRAM 200
according to this embodiment. Referring to FIG. 4, synchronous
pseudo-SRAM 200 according to the embodiment includes a DRAM cell
array and peripheral circuit group 201, and a control circuit
202.
[0152] A DRAM cell array in DRAM cell array and peripheral circuit
group 201 is a memory array formed of cells of a Dynamic Random
Access Memory (DRAM), and has four banks. The banks are memory cell
groups formed by dividing the DRAM cell array, and each forms a
unit to be refreshed at a time. Thus, one refresh operation
refreshes one bank.
[0153] The peripheral circuit group includes global I/O line pair
GIOP (GIO and /GIO), column select lines provided corresponding to
respective columns, column select gates, sense amplifiers,
preamplifier, a write driver, a row decoder, a column decoder and
others.
[0154] Control circuit 202 includes a command decoder 214, a
refresh bank address designating circuit 213, a refresh timer 212,
a refresh control circuit 211 and a WAIT control circuit 215.
[0155] Command decoder 214 produces a row activating signal ACT,
read signal READ and write signal WRITE in accordance with a
combination of logical levels of internal control signals produced
according to external control signals.
[0156] Refresh timer 212 is formed of a ring oscillator, and
provides a refresh cycle signal /Refcyc, which cyclically becomes
active.
[0157] Refresh bank address designating circuit 213 receives
refresh cycle signal /Refcyc, read or write signal READ or WRITE,
and a bank address, and designates the address of the bank to be
refreshed and the timing of such refreshing.
[0158] When refresh control circuit 211 receives only the bank
address from refresh bank address designating circuit 213, it
immediately controls the operation of refreshing the bank in the
received address. When refresh control circuit 211 receives the
bank address provided from refresh bank address designating circuit
213 as well as an instruction to the effect that the refreshing is
to be performed after the reading is effected on the bank in the
received address, it controls the operation of refreshing the bank
in question after a predetermined time elapses.
[0159] WAIT control circuit 215 keeps the WAIT signal at the level
of "L" while refresh control circuit 211 is controlling the refresh
operation.
[0160] FIG. 5 shows a specific structure of a refresh bank address
designating circuit 213. Referring to FIG. 5, refresh bank address
designating circuit 213 includes an OR circuit 221, a bank address
counter 222, a refresh-execution/nonexecution determining circuit
223, a refreshed bank holding circuit 224, a first comparing
circuit 225, a second comparing circuit 227, and a read/write
operation bank detecting circuit 226.
[0161] When OR circuit 221 receives refresh cycle signal /Refcyc
provided from refresh timer 212, a signal NEXT provided from
refresh-execution/nonexecution determining circuit 223 for
designating a next bank, or signal NEXT provided from first
comparing circuit 225 for designating a next bank, OR circuit 221
provides a count-up signal.
[0162] When bank address counter 222 receives the count-up signal,
it increments the count within a range from 1 to 4. The initial
value of the count is equal to "0", and the count of "4" will
change to "1".
[0163] Refreshed bank holding circuit 224 holds the address of the
refreshed bank. When refreshed bank holding circuit 224 holds all
the bank addresses of "1"-"4", it then erases all the bank
addresses held therein, and resets the count of bank address
counter 222 to "0". Therefore, by performing the refresh four
times, all the banks 1-4 are refreshed.
[0164] Refresh-execution/nonexecution determining circuit 223
determines whether refreshed bank holding circuit 224 holds the
bank address corresponding to the count of bank address counter 222
or not. If refreshed bank holding circuit 224 holds the bank
address corresponding to the count, it determines that the refresh
is not yet executed, and provides the bank address in question to
first or second comparing circuit 225 or 227. If the bank address
to be provided is the last one bank address, which is not held in
refreshed bank holding circuit 224, refresh-execution/nonexecution
determining circuit 223 provides the bank address to second
comparing circuit 227. Otherwise, refresh-execution/nonexecution
determining circuit 223 provides the bank address to first
comparing circuit 225.
[0165] If the bank address corresponding to the count is held,
refresh-execution/nonexecution determining circuit 223 determines
that the refresh is already executed, and provides signal NEXT
designating a next bank address.
[0166] When read/write operation bank detecting circuit 226
receives read signal READ or write signal WRITE, it provides the
applied bank address (i.e., the address of the bank, on which
reading or writing is effected) to first and second comparing
circuits 225 and 227.
[0167] First comparing circuit 225 determines whether the two bank
addresses, which are received from read/write operation bank
detecting circuit 226 refresh-execution/nonexecution determining
circuit 223, respectively, are the same or not. If these addresses
are different from each other, first comparing circuit 225 provides
the bank address received from refresh-execution/nonexecution
determining circuit 223 to refresh control circuit 211, and also
provides this bank address to refreshed bank holding circuit 224
for holding it therein. When the two bank addresses are the same,
first comparing circuit 225 provides signal NEXT designating a next
bank address.
[0168] Second comparing circuit 227 determines whether the two bank
addresses received from read/write operation bank detecting circuit
226 and refresh-execution/nonexecution determining circuit 223 are
the same or not. If these addresses are different from each other,
second comparing circuit 227 provides the bank address received
from refresh-execution/nonexecution determining circuit 223 to
refresh control circuit 211, and also provides this bank address to
refreshed bank holding circuit 224 for holding it therein. When the
two bank addresses are the same, second comparing circuit 227
provides to refresh control circuit 211 the bank address received
from refresh-execution/nonexecution determining circuit 223 as well
as an instruction to the effect that the refresh is to be performed
after the reading is effected on the bank in the address in
question.
[0169] (Example of Operation of Synchronous Pseudo-SRAM in the
Background Art)
[0170] First, an operation of a synchronous pseudo-SRAM in the
background art will be described for comparison with that of
synchronous pseudo-SRAM 200 of this embodiment.
[0171] FIG. 6 illustrates an operation of a synchronous pseudo-SRAM
in the prior art. As illustrated in FIG. 6, if a refresh timer
provides a refresh cycle signal /Refcyc while a read operation is
being performed based on read signal READ according to an external
instruction, a refresh control circuit will start the control of
the refresh operation after the end of the read operation, which is
being performed. A WAIT control circuit externally provides a WAIT
signal during execution of the refresh operation.
[0172] In the synchronous pseudo-SRAM, therefore, when the timing
of the read operation overlaps with the timing of the self-refresh,
the timing of the self-refresh is delayed, and the read instruction
cannot be externally provided to the synchronous pseudo-SRAM until
the end of the self-refresh.
[0173] (Operation Example 1 of Synchronous Pseudo-SRAM 200 of the
Embodiment)
[0174] FIG. 7 illustrates an operation example of synchronous
pseudo-SRAM 200 according to the embodiment.
[0175] First, a read operation is effected on bank 2 based on read
signal READ externally designating bank 2,
[0176] Then, a read operation is effected on bank 3 based on read
signal READ externally designating bank 3. During the read
operation of bank 3, refresh timer 212 provides refresh cycle
signal /Refcyc. OR circuit 221 in refresh bank address designating
circuit 213 provides the count-up signal when it receives refresh
cycle signal /Refcyc. Bank address counter 222 sets the count of
bank address to "1". Since refreshed bank holding circuit 224 has
not yet held any bank data, refresh-execution/nonexecution
determining circuit 223 determines that the refresh is not yet
executed, and provides the bank address "1" to first comparing
circuit 225. Read/write operation bank detecting circuit 226
receives read signal READ and the bank address "3", and issues the
bank address "3" to first and second comparing circuits 225 and
227. Since first comparing circuit 225 receives the two bank
addresses different from each other, it sends the bank address "1"
received from refresh-execution/nonexecution determining circuit
223 to refresh control circuit 211, and provides the bank address
"1" to refreshed bank holding circuit 224 for holding it therein.
When refresh control circuit 211 receives the bank address "1", it
controls the refresh operation to be effected on bank 1.
[0177] Then, based on read signal READ externally designating bank
1, the read operation is effected on bank 1.
[0178] Then, based on read signal READ externally designating bank
2, the read operation is effected on bank 2. During the read
operation of bank 2, refresh timer 212 provides refresh cycle
signal /Refcyc. When OR circuit 221 in refresh bank address
designating circuit 213 receives refresh cycle signal /Refcyc, OR
circuit 221 provides the count-up signal. Bank address counter 222
sets the count of the bank address to "2". Since refreshed bank
holding circuit 224 holds only the bank address "1", and does not
hold the bank address "2", refresh-execution/nonexecution
determining circuit 223 determines that the refresh is not
executed, and provides the bank address "2" to first comparing
circuit 225. Read/write operation bank detecting circuit 226
receives read signal READ and the bank address "2", and provides
the bank address "2" to first and second comparing circuits 225 and
227. Since the received two bank addresses are the same, first
comparing circuit 225 receives provides signal NEXT designating the
next bank.
[0179] When OR circuit 221 receives signal NEXT designating the
next bank, it provides the count-up signal. Bank address counter
222 sets the count of the bank address to "3". Since refreshed bank
holding circuit 224 holds only the bank address "1", and does not
hold the bank address "3", refresh-execution/nonexecution
determining circuit 223 determines that the refresh is not yet
executed, and provides the bank address "3" to first comparing
circuit 225. Read/write operation bank detecting circuit 226
receives read signal READ and the bank address "2", and provides
the bank address "2" to first and second comparing circuits 225 and
227. Since first comparing circuit 225 receives the two bank
addresses different from each other, it sends the bank address "3"
received from refresh-execution/nonexecution determining circuit
223 to refresh control circuit 211, and provides the bank address
"3" to refreshed bank holding circuit 224 for holding it therein.
When refresh control circuit 211 receives the bank address "3", it
controls the operation of refreshing bank 3.
[0180] Then, the read operation is effected on bank 4 based on read
signal READ externally designating bank 4.
[0181] Then, the read operation is effected on bank 1 based on read
signal READ externally designating bank 1. During the read
operation of bank 1, refresh timer 212 provides refresh cycle
signal /Refcyc. When OR circuit 221 in refresh bank address
designating circuit 213 receives refresh cycle signal /Refcyc, OR
circuit 221 provides the count-up signal. Bank address counter 222
sets the count of the bank address to "4". Since refreshed bank
holding circuit 224 holds only the bank addresses "1" and "3", and
does not hold the bank address "4", refresh-execution/nonexecution
determining circuit 223 determines that the refresh is not yet
executed, and provides the bank address "4" to first comparing
circuit 225. Read/write operation bank detecting circuit 226
receives read signal READ and the bank address "1", and provides
the bank address "1" to first and second comparing circuits 225 and
227. Since first comparing circuit 225 receives the two bank
addresses different from each other, it sends the bank address "4"
received from refresh-execution/nonexecution determining circuit
223 to refresh control circuit 211, and provides the bank address
"4" to refreshed bank holding circuit 224 for holding it therein.
When refresh control circuit 211 receives the bank address "4", it
controls the operation of refreshing bank 4.
[0182] Then, the read operation is effected on bank 3 based on read
signal READ externally designating bank 3.
[0183] Then, the read operation is effected on bank 4 based on read
signal READ externally designating bank 4. During the read
operation of bank 4, refresh timer 212 provides refresh cycle
signal /Refcyc. When OR circuit 221 in refresh bank address
designating circuit 213 receives refresh cycle signal /Refcyc, OR
circuit 221 provides the count-up signal. Bank address counter 222
sets the count of the bank address to "1" (and thus cyclically
renews it). Since refreshed bank holding circuit 224 holds the bank
addresses "1", "3" and "4", refresh-execution/nonexecution
determining circuit 223 determines that the refresh is already
executed, and provides signal NEXT designating the next bank.
[0184] When OR circuit 221 receives signal NEXT designating the
next bank, it provides the count-up signal. Bank address counter
222 sets the count of the bank address to "2". Since refreshed bank
holding circuit 224 holds the bank addresses "1", "3" and "4", and
does not hold the bank address "2", refresh-execution/nonexecution
determining circuit 223 determines that the refresh is not yet
executed, and provides the bank address "2" to second comparing
circuit 227. In this operation, the bank address "2" is provided
not to first comparing circuit 225 but to second comparing circuit
227 because the bank of bank address "2" is the unrefreshed last
bank among those of the bank addresses "1"-"4". Read/write
operation bank detecting circuit 226 receives read signal READ and
the bank address "4", and provides the bank address "4" to first
and second comparing circuits 225 and 227. Since second comparing
circuit 227 receives the two bank addresses different from each
other, it sends the bank address "2" received from
refresh-execution/nonexecution determining circuit 223 to refresh
control circuit 211, and provides the bank address "2" to refreshed
bank holding circuit 224 for holding it therein. When refresh
control circuit 211 receives the bank address "2", it controls the
operation of refreshing bank 2.
[0185] When refreshed bank holding circuit 224 holds all the bank
addresses "1"-"4", it erases the bank addresses held therein, and
causes bank address counter 222 to reset the count of bank address
to "0".
[0186] (Operation Example 2 of Refresh Bank Address Designating
Circuit)
[0187] FIG. 8 illustrates another example of the operation of
synchronous pseudo-SRAM 200 according to the embodiment.
[0188] In the last stage of the operation example 1, if read signal
READ externally designating bank 2 is input instead of read signal
READ designating bank 4, processing is performed as follows.
[0189] Then, the read operation is effected on bank 2 based on read
signal READ externally designating bank 2. During the read
operation of bank 2, refresh timer 212 provides refresh cycle
signal /Refcyc. OR circuit 221 in refresh bank address designating
circuit 213 provides the count-up signal when it receives refresh
cycle signal /Refcyc. Bank address counter 222 sets the count of
bank address to "1" (and thus cyclically renews it). Since
refreshed bank holding circuit 224 holds the bank addresses "1",
"3" and "4", refresh-execution/nonexecution determining circuit 223
determines that the refresh is already executed, and provides
signal NEXT designating the next bank.
[0190] When OR circuit 221 receives signal NEXT designating the
next bank, it provides the count-up signal. Bank address counter
222 sets the count of the bank address to "2". Since refreshed bank
holding circuit 224 holds the bank addresses "1", "3" and "4", and
does not hold the bank address "2", refresh-execution/nonexecution
determining circuit 223 determines that the refresh is not yet
executed, and provides the bank address "2" to second comparing
circuit 227.
[0191] In this operation, the bank address "2" is provided not to
first comparing circuit 225 but to second comparing circuit 227
because the bank of bank address "2" is the unrefreshed last bank
among those of the bank addresses "1"-"4". Read/write operation
bank detecting circuit 226 receives read signal READ and the bank
address "2", and provides the bank address "2" to first and second
comparing circuits 225 and 227. Since second comparing circuit 227
receives the same two bank addresses, it sends the bank address "2"
received from refresh-execution/nonexecution determining circuit
223 as well as an instruction to the effect that the refresh is to
be performed after the end of read operation of bank 2 to refresh
control circuit 211, and provides the bank address "2" to refreshed
bank holding circuit 224 for holding it therein. When refresh
control circuit 211 receives the bank address "2" as well as the
instruction to the effect that the refresh is to be performed after
the end of read operation of bank 2, refresh control circuit 211
controls the operation of refreshing bank 2 after elapsing of a
predetermined time.
[0192] When refreshed bank holding circuit 224 holds all the bank
addresses "1"-"4", it erases the bank addresses held therein, and
causes bank address counter 222 to reset the count of bank address
to "0".
[0193] According to the synchronous pseudo-SRAM of the embodiment,
as described above, the bank not overlapping with the banks, on
which the reading or writing is to be effected, and not yet
refreshed is determined as the bank to be refreshed. Therefore, the
self-refresh can be effected on the respective banks at
substantially equal frequencies without delay in timing.
[0194] According to the embodiment, refreshing of all the four
banks is completed by the four refresh operations such as first to
fourth refresh operations or by fifth to eighth refresh operations.
However, this is not restrictive. For example, such a manner may be
employed that refreshing of all the four banks is completed every
time the self-refresh is performed eight times. If this manner is
employed in the operation example 2, the fourth operation of
self-refreshing bank 2 can be performed without a delay in timing.
Further, such a manner may be employed that a schedule of the bank
addresses to be read can be designated on the external system side
prior to read signal READ. In this case, the schedule of the bank
addresses of the banks to be refreshed can be set such that the
refreshing may not overlap with the schedule-designated reading of
the bank addresses, and the respective banks may be refreshed equal
times.
[0195] Although the operation examples of the embodiment have been
described in connection with the case where the refresh request is
issued during the read operation. However, similar processing can
be performed in the case where the refresh request is issued during
the write operation.
[0196] This embodiment is not restrictively applied to the
synchronous pseudo-SRAM, and may be applied to the synchronous
pseudo-SRAM, which does not operate in synchronization with the
clock.
Third Embodiment
[0197] A third embodiment relates to a structure, in which a
plurality of synchronous pseudo-SRAMs are accommodated in one
package, and are configured to be refreshed according to the same
timing.
[0198] (Structure)
[0199] FIG. 9 shows a structure of one of synchronous pseudo-SRAMs
300 accommodated in one package according to this embodiment.
Synchronous pseudo-SRAM 300 includes a refresh timer 301, a control
circuit 302 and a DRAM cell array and peripheral circuit group 303,
and a switch 304.
[0200] The DRAM cell array in DRAM cell array and peripheral
circuit group 303 is a memory array formed of cells of a Dynamic
Random Access Memory (DRAM). The peripheral circuit group includes
global I/O line pair GIOP (GIO and /GIO), column select lines
provided corresponding to respective columns, column select gates,
sense amplifiers, preamplifiers, a write driver, a row decoder, a
column decoder and others.
[0201] Control circuit 302 receives external control signals
provided via a control signal terminal 315 as well as write data
provided via a data I/O terminal 316 for the DRAM cell array, and
controls the whole processing of synchronous pseudo-SRAM 300 based
on these received signal and data. Also, control circuit 302
provides read data read from the DRAM array via data I/O terminal
316. Control circuit 302 includes a refresh control circuit 305 and
a WAIT control circuit 306.
[0202] Refresh timer 301 is formed of a ring oscillator, and
provides refresh cycle signal /Refcyc, which cyclically becomes
active, to switch 304 and a refresh timer output PAD 311. Refresh
cycle signal /Refcyc provided to refresh timer output PAD 311 is
sent to another synchronous pseudo-SRAM.
[0203] A refresh timer input PAD 312 receives refresh cycle signal
/Refcyc from a refresh timer of another synchronous
pseudo-SRAM.
[0204] A bonding option PAD 313 controls switch 304 according to a
potential applied thereto.
[0205] Switch 304 receives refresh cycle signal /Refcyc provided
from refresh timer 301 as well as refresh cycle signal /Refcyc
provided from refresh timer input PAD 312. These two refresh cycle
signals /Refcyc have the same period, but differ in timing from
each other.
[0206] Switch 304 provides one of received refresh cycle signals
/Refcyc to refresh control circuit 305 according to the potential
applied to bonding option PAD 313. More specifically, when a ground
potential is applied to bonding option PAD 313, switch 304 provides
refresh cycle signal /Refcyc received from refresh timer input PAD
312. When a potential other than the ground potential is applied to
bonding option PAD 313, switch 304 provides refresh cycle signal
/Refcyc received from refresh timer 301.
[0207] Refresh control circuit 305 controls the self-refresh.
[0208] FIG. 10 shows a specific structure of refresh control
circuit 305. Referring to FIG. 10, refresh control circuit 305
includes an instruction signal activating circuit 50, a determining
circuit 60, NAND gates 41 and 44, an inverter 42, a buffer 48,
delay circuits 43 and 49, and a flip-flop 45.
[0209] Instruction signal activating circuit 50 provides refresh
cycle signal /Refcyc for activating a refresh instructing signal
/REFE. Deteimining circuit 60 provides a determining signal Refwin
for determining whether refresh instructing signal /REFE activated
by a refresh flag signal Refflag is to be output or not.
[0210] NAND gate 41 receives refresh flag signal Refflag and
determining signal Refwin, carries out the logical AND between
refresh signal flag Refflag and determining signal Refwin, and
provides a signal produced by inverting a result of the AND as an
inverted AND signal /REFSF.
[0211] Inverter 42 receives and inverts signal /REFSF provided from
NAND gate 41 to provide a signal .phi.A1. Delay circuit 43 receives
inverted AND signal /REFSF, and delays it by a predetermined
time.
[0212] NAND gate 44 receives output signal .phi.A1 of inverter 42
and the output signal of delay circuit 43, carries out the logical
AND between signal .phi.A1 and the output signal of delay circuit
43, and inverts the result of the AND to provide a signal
/REFS.
[0213] Flip-flop 45 is formed of NAND gates 46 and 47. NAND gate 46
receives signal /REFS and an output signal .phi.A3 provided from
NAND gate 47, carries out the logical AND between signal /REFS and
signal .phi.A3, and inverts the result of the AND to provide a
signal .phi.A2. NAND gate 47 receives signal .phi.A2 provided from
NAND gate 46 and a signal .phi.A4 provided from delay circuit 49,
carries out the logical AND between signals .phi.A2 and .phi.A4,
inverts the result of the AND, and provides the result thus
inverted as refresh instructing signal /REFE. The refresh operation
is performed according to the activation of refresh instructing
signal /REFE.
[0214] Delay circuit 49 receives refresh instructing signal /REFE
provided from flip-flop 45, and delays it by a constant time to
provide signal .phi.A4.
[0215] Buffer 48 receives signal .phi.A3, and provides refresh
instructing signal /REFE.
[0216] Instruction signal activating circuit 50 includes a
flip-flop 52, a NAND gate 55, inverters 56 and 57, and a delay
circuit 58.
[0217] Flip-flop 52 is formed of NAND gates 53 and 54. NAND gate 53
receives refresh cycle signal /Refcyc and an output signal .phi.A11
of NAND gate 54, carries out the logical AND between refresh cycle
signal /Refcyc and signal .phi.A11, and inverts the result of the
AND to provide a signal .phi.A10. NAND gate 54 receives output
signal .phi.A10 of NAND gate 53 and an output signal .phi.A12 of
NAND gate 55, carries out the logical AND between signals .phi.A10
and .phi.A12, and inverts the result of the AND to provide signal
.phi.A11.
[0218] Inverter 56 receives and inverts signal .phi.A11 provided
from flip-flop 52 to provide the inverted signal as refresh flag
signal Refflag.
[0219] Inverter 57 receives and inverts refresh instructing signal
/REFE. Delay circuit 58 receives refresh instructing signal /REFE
inverted by inverter 57, and delays the inverted refresh
instructing signal /REFE by a constant time to provide a signal
.phi.A13.
[0220] NAND gate 55 receives refresh instructing signal /REFE and
signal .phi.A13 provided from delay circuit 58, carries out the
logical AND between refresh instructing signal /REFE and signal
.phi.A13, and inverts the result of the AND to provide signal
.phi.A12.
[0221] Determining circuit 60 is formed of a buffer circuit 61.
Buffer circuit 61 receives internal chip enable signal ZINTCE, and
provides determining signal Refwin.
[0222] Referring to FIG. 9 again, WAIT control circuit 306 keeps a
WAIT signal, which is output from a WAIT terminal 314, at the level
of "L" while refresh control circuit 305 is performing the refresh
control.
[0223] (Package)
[0224] FIG. 11 shows a structure of a package accommodating two
synchronous pseudo-SRAMs according to the embodiment. Referring to
FIG. 11, first and second synchronous pseudo-SRAMs 300a and 300b
have structures similar to that of the synchronous pseudo-SRAM
shown in FIG. 9. A bonding option PAD 313a of first synchronous
pseudo-SRAM 300a is open, and a switch 304a sends refresh cycle
signal /Refcyc provided from a refresh timer 301a to a refresh
control circuit 305a.
[0225] A bonding option PAD 313b of second synchronous pseudo-SRAM
300b is supplied with a ground potential, and a switch 304b
receives refresh cycle signal /Refcyc, which is provided from
refresh timer 301a of first synchronous pseudo-SRAM 300a, via a
refresh timer input 312b, and provides it to a refresh control
circuit 305b. Thereby, both refresh control circuits 305a and 305b
operate according to refresh cycle signal /Refcyc provided from
refresh timer 301a so that first and second synchronous
pseudo-SRAMs 300a and 300b are refreshed according to the same
timing.
[0226] A WAIT control circuit 306a provides a WAIT signal via WAIT
terminals 314a and 314, and a WAIT control circuit 306b provides a
WAIT signal via WAIT terminals 314b and 314. Since refresh control
circuits 305a and 305b perform the refresh according to the same
timing, the respective WAIT signals change to "L" according to the
same timing.
[0227] In the plurality of synchronous pseudo-SRAMs, as described
above, the levels of WAITs notifying that an externally instructed
operation cannot be accepted due to refreshing, which is being
performed, can be changed according to the same timing.
[0228] Although the embodiment has been described in connection
with an example of the package including the two synchronous
pseudo-SRAMs, the plurality of synchronous pseudo-SRAMs more than
one may be packaged.
[0229] In this embodiment, the plurality of synchronous
pseudo-SRAMs shares refresh cycle signal /Refcyc, output their own
refresh cycle signal /Refcyc via refresh timer output PADs,
respectively, and each receive refresh cycle signal /Refcyc of the
other synchronous pseudo-SRAM via the refresh timer input PAD.
However, this is not restrictive. For example, the plurality of
synchronous pseudo-SRAMs may share refresh flag signal Refflag,
inverted AND signal /REFSF or refresh instructing signal /REFE, and
may operate to transmit and receive these signal via refresh timer
output PAD and refresh timer input PAD.
[0230] According to the embodiment, each of the synchronous
pseudo-SRAMs provides the WAIT signal. However, this is not
restrictive. For example, switches, which can be controlled by
bonding option PADs, may be arranged between WAIT control circuit
306a and WAIT terminal 314a and between WAIT control circuit 306b
and WAIT terminal 314b, respectively. These switches may be
controlled such that only one of the switches connects the WAIT
terminal and the WAIT control circuit, and thereby only one of the
synchronous pseudo-SRAMs may output the WAIT signal.
[0231] Further, in a certain case, the plurality of synchronous
pseudo-SRAMs do not output the WAIT signal, i.e., in the case where
the timing of the self-refresh overlaps with the timing of
externally applied read signal READ or write signal WRITE, read
signal READ or write signal WRITE is held, and the read operation
or the write operation will be performed after the end of the
self-refresh. In this case, the plurality of synchronous
pseudo-SRAMs may share only refresh cycle signal /Refcyc. Thus, the
control of WAIT is not performed. Even in this case, since the
plurality of synchronous pseudo-SRAMs performs the refresh at the
same time, such a certain effect can be achieved that interference
between signals can be suppressed.
[0232] This embodiment is not restrictively applied to the
synchronous pseudo-SRAM, and may be applied to various synchronous
pseudo-SRAM operating in synchronization with clocks.
Fourth Embodiment
[0233] A fourth embodiment relates to a synchronous pseudo-SRAM
performing burst read/write in such a manner that several bits
starting from the leading bit are read or written according to a
first clock, at which the read or write signal is produced, and the
remaining bits are read or written according to the second or later
clocks defined by a command latency CL.
[0234] (Structure)
[0235] FIG. 12 shows a structure of a synchronous pseudo-SRAM 400
according to the embodiment. Referring to FIG. 12, synchronous
pseudo-SRAM 400 includes a DRAM cell array 401, a control circuit
402, an address buffer 403, a RCR (Refresh Configuration Register)
404, a BCR (Bus Configuration Register) 405, and an I/O circuit and
buffer 406.
[0236] DRAM cell array 401 is a memory array formed of cells of a
Dynamic Random Access Memory (DRAM).
[0237] I/O circuit and buffer 406 performs input/output of data
from and to an external system side via a data I/O terminal DQ. I/O
circuit and buffer 406 provides data, which is output from the DRAM
cells, in synchronization with a clock signal CLKQ applied from an
I/O control circuit 411.
[0238] RCR 404 defines a manner of self-refresh.
[0239] BCR 405 stores an interface to the external systems, and
thus stores, e.g., a burst length BL and command latency CL.
[0240] Address buffer 403 receives an external address signal
ADD[21:0], and produces an internal address signal. According to
the synchronous pseudo-SRAM, address buffer 403 takes in external
address signal ADD[21:0] when an external address take-in signal
ADV# is at "L". External address take-in signal ADV# attains "L"
according to timing earlier than that of production of read signal
READ or write signal WRITE. External address signal ADD[21:0] thus
applied includes not only a row address but also a column address.
Therefore, the row and column addresses are obtained prior to the
production of read or write signal READ or WRITE.
[0241] As described above, since not only the row address but also
the column address are obtained prior to production of the read or
write signal READ or WRITE, the column access can be started after
the row access without waiting for the input of the clock defined
by command latency CL. This embodiment utilizes the above features,
and the column access processing for reading the data from the
leading column in the burst access is performed according to the
clock (first clock), at which read or write signal READ or WRITE is
produced. Also, column access processing for reading the data from
the remaining columns in the burst access is performed according to
a clock (second clock) defined by command latency CL.
[0242] Control circuit 402 includes a command decoder 410, an I/O
control circuit 411, a row control circuit 409, a column control
circuit 407, a WAIT control circuit 412 and a refresh control
circuit 420.
[0243] Command decoder 410 produces row activating signal ACT, read
signal READ and write signal WRITE according to a combination of
logical levels of the internal control signals produced from the
external control signals.
[0244] Row control circuit 409 produces a column enable signal COLE
as well as a sense amplifier activating signal SENSE activating the
sense amplifier, which is connected to a bit line pair BL and ZBL
arranged between the memory cells and global bit line pair GIO and
ZGIO. FIG. 13 shows a structure of a row control circuit 409.
Referring to FIG. 13, a delay circuit (Delay) DL101 receives row
activating signal ACT to be activated in response to the rising of
a first clock CLK0, i.e., a clock, at which read signal READ or
write signal WRITE is produced. Delay circuit (Delay) DL101
provides sense amplifier activating signal SENSE by delaying row
activating signal ACT. A delay circuit (Delay) DL102 receives sense
amplifier activating signal SENSE, and produces column enable
signal COLE by delaying sense amplifier activating signal
SENSE.
[0245] Column control circuit 407 produces a preamplifier
activating signal PRAM activating the preamplifier connected to
global bit line pair GIO and ZGIO, and also produces a column
decoder activation trigger signal CDETRG. FIG. 14 fragmentarily
shows a structure of column control circuit 407. Referring to FIG.
14, column control circuit 407 includes a COLP_SHFT generator 422
and a CDETRG generator 421.
[0246] COLP_SHFT generator 422 produces a column shift signal
COLP_SHFT based on external clock CLK, read signal READ (or write
signal WRITE) and command latency CL as well as a number N1 (equal
to one in this embodiment) of a bit(s) read at first clock CLK0,
i.e., a clock, at which read signal READ (or write signal WRITE) is
produced, and burst length BL. Thus, COLP_SHFT generator 422
activates column shift signal COLP_SHFT in accordance with falling
of a (CL-N1)th clock CLK after the clock, at which read signal READ
(or write signal WRITE) is produced. Also, COLP_SHFT generator 422
deactivates column shift signal COLP_SHFT in accordance with the
fact that the count of the burst length counter attains burst
length BL.
[0247] CDETRG generator 421 produces column decoder activation
trigger signal CDETRG based on column shift signal COLP_SHFT,
external clock CLK and column enable signal COLE.
[0248] FIG. 15 shows a specific structure of CDETRG generator 421.
Referring to FIG. 15, CDETRG generator 421 includes a one-shot
pulse generator 431, an AND circuit AND41 and an OR circuit OR42.
One-shot pulse generator 431 produces a one-shot pulse at a level
of "H" in response to the rising of column enable signal COLE. This
one-shot pulse forms a signal activating the first column to be
accessed in synchronization with first clock CLK0.
[0249] AND circuit AND41 provides a clock pulse at the level of "H"
when column enable signal COLE is at "H" and COLP_SHFT is at "H".
This clock pulse forms a signal activating second to fourth columns
to be accessed in synchronization with second clock CLK2 and
subsequent clocks.
[0250] OR circuit OR42 combines the one-shot pulse provided from
one-shot pulse generator 431 and the clock pulse provided from AND
circuit AND41. The pulse thus combined forms a pulse of column
decoder activation trigger signal CDETRG.
[0251] FIG. 16 shows a structure of WAIT control circuit 412.
Referring to FIG. 16, WAIT control circuit 412 includes a WAIT_ASYN
generating circuit 432 and a WAIT generating circuit 433.
[0252] WAIT_ASYN generating circuit 432 sets the WAIT_ASYN signal
to "L" in response to the fact that read signal READ or write
signal WRITE is provided from command decoder 410 and external chip
enable signal CE# is active and thus at "L". Then, WAIT_ASYN
generating circuit 432 sets the WAIT_ASYN signal to "H" after
elapsing of a predetermined time, which is required for outputting
data D0 of the first or leading bit from data output terminal DQ
after reception of a preamplifier activating signal PAE.
Thereafter, WAIT_ASYN generating circuit 432 sets the WAIT_ASYN
signal to "Hi-Z" in response to deactivation of external chip
enable signal CE#.
[0253] WAIT generating circuit 433 sets the WAIT signal to "L" in
response to the fact that read signal READ or write signal WRITE is
input from command decoder 410, and external chip enable signal CE#
is active and thus at "L". Then, WAIT generating circuit 433
activates the WAIT signal to attain "H" after it receives the
clocks equal in number to ((CL-1)+(number N1 of bits to be read at
first clock CLK0, i.e., the clock, at which read signal READ or
write signal WRITE is produced)). Thereafter, WAIT generating
circuit 433 sets the WAIT signal to "Hi-Z" in response to the
deactivation (i.e., "H") of external chip enable signal CE#.
[0254] (Timing of WAIT Signal of Synchronous Pseudo-SRAM in the
Background Art)
[0255] FIG. 17 illustrates timing of the WAIT signal of the
synchronous pseudo-SRAM in the prior art. As illustrated in FIG.
17, the WAIT signal attains "L" in response to the fact that read
signal READ is input and external chip enable signal CE# is active
and thus at "L". Then, the WAIT signal attains "H" after receiving
the clocks of (CL-1) in number, where CL is equal to 3. Then, the
WAIT signal attains "Hi-Z" in response to the deactivation (i.e.,
setting to "H") of external chip enable signal CE#.
[0256] (Timing of WAIT_ASYN Signal and WAIT Signal of Synchronous
Pseudo-SRAM 400 of the Embodiment)
[0257] FIG. 18 illustrates timing of the WAIT_ASYN signal and WAIT
signal of synchronous pseudo-SRAM 400 of the embodiment. As
illustrated in FIG. 18, the WAIT_ASYN signal attains "L" in
response to the fact that read signal READ is input and external
chip enable signal CE# is active and thus at "L". Then, the
WAIT_ASYN signal attains "H" after elapsing of a predetermined
time, which is required for outputting data D0 of the leading bit
from data output terminal DQ after preamplifier activating signal
PAE is received. Thereby, it is possible to notify the external
system side of the timing of output of data D0 of the leading bit,
which is column-accessed according to clock CLK0. Then, the
WAIT_ASYN signal attains "Hi-Z" in response to the deactivation
(i.e., setting to "H") of external chip enable signal CE#.
[0258] As illustrated in FIG. 18, the WAIT signal attains "L" in
response to the fact that read signal READ is input and external
chip enable signal CE# is active and thus at "L". Then, the WAIT
signal attains "H" after receiving the clocks of (CL-1+N1) in
number, where CL is equal to 3 and N1 is equal to one. Thereby, it
is possible to notify the external system side of the timing of
output of data D1 of the leading bit, which is column-accessed
according to the clock determined based on command latency CL.
Then, the WAIT signal attains "Hi-Z" in response to the
deactivation (i.e., setting to "H") of external chip enable signal
CE#.
[0259] Referring to FIG. 12 again, a peripheral circuit group 408
includes a row decoder 418, a column decoder 417, sense amplifiers
(not shown) and preamplifiers (not shown).
[0260] Row decoder 418 activates the selected word line.
[0261] FIG. 19 shows a structure of column decoder 417. As shown in
FIG. 19, when column decoder activation trigger signal CDETRG
becomes active, column decoder 417 activates a column select signal
CSL corresponding to the column address applied thereto.
[0262] The sense amplifier, which is not shown, is a first
amplifier circuit, and amplifies a potential difference between
paired bit lines BL and ZBL.
[0263] The preamplifier, which is not shown, is a second amplifier
circuit, and increases a potential difference between paired global
bit lines GIO and ZGIO connected to the plurality of paired bit
lines BL and ZBL.
[0264] Refresh control circuit 420 in FIG. 12 controls the
self-refresh operation of the DRAM cell array based on an internal
refresh timer (not shown).
[0265] (Operation of Synchronous Pseudo-SRAM of the Embodiment)
[0266] FIG. 20 is a timing chart illustrating an operation of the
synchronous pseudo-SRAM of the embodiment. Referring to FIG. 20,
row access processing is performed as follows in synchronization
with the rising of clock CLK0 (first clock), at which read signal
READ is produced.
[0267] Command decoder 410 provides a row activating signal ACT,
which is activated in synchronization with clock CLK0.
[0268] Row decoder 418 selects and activates the word line based on
the row address sent from address buffer 403.
[0269] Row control circuit 409 activates sense amplifier enable
signal SENSE with a delay from row activating signal ACT. Thereby,
the sense amplifier (not shown) in peripheral circuit group 408
amplifies the potentials on the bit line pair.
[0270] Row control circuit 409 activates column enable signal COLE
with a delay from sense amplifier activating signal SENSE.
[0271] Then, column access processing is effected on the first
column in synchronization with the rising of first clock CLK0.
[0272] CDETRG generator 421 produces a one-shot pulse at the rising
of column enable signal COLE. This forms the first pulse of column
decoder activation trigger signal CDETRG.
[0273] Column decoder 417 activates column select signal CSL
corresponding to the column address of the first column applied
thereto in accordance with the first pulse of column decoder
activation trigger signal CDETRG.
[0274] The potentials on the bit line pair of the first column
selected by column select signal CSL are sent to the preamplifier
(not shown) in peripheral circuit group 408, and are amplified
thereby.
[0275] The data of the first column amplified by the preamplifier
is sent to the I/O circuit and buffer 406. I/O control circuit 411
receives external clock CLK, and provides internal clock signal
CLKQ. In response to the rising of first clock CLK0, the pulse of
leading clock signal CLKQ is produced.
[0276] I/O circuit and buffer 406 externally provides data D0,
which is provided from the first column, via data output terminal
DQ in synchronization with clock signal CLKQ.
[0277] Then, the column access processing is effected on the second
to fourth columns in synchronization with the clocks starting from
(CL-N1)th clock (i.e., second, clock CLK2) after first clock
CLK0.
[0278] COLP_SHFT generator 422 activates column shift signal
COLP_SHFT in accordance with the falling of clock CLK2 (second
clock), and deactivates column shift signal COLP_SHFT in accordance
with the fact that the count of the burst length counter attains
burst length BL.
[0279] CDETRG generator 421 extracts three clock pulses included in
a period of "H" of column shift signal COLP_SHFT. These clock
pulses form second to fourth pulses of column decoder activation
trigger signal CDETRG, respectively.
[0280] Column decoder 417 activates column select signal CSL
corresponding to the received column addresses of the second to
fourth columns in accordance with the second to fourth pulses of
column decoder activation trigger signal CDETRG.
[0281] The potentials on the bit line pairs of the second to fourth
columns selected by column select signal CSL are sent to the
preamplifier (not shown), and are amplified.
[0282] The data of the second to fourth columns amplified by the
preamplifier are sent to I/O circuit and buffer 406. I/O control
circuit 411 receives externally applied clock signal CLK, and
provides internal clock signal CLKQ. The timing of the second to
fourth pulses of clock signal CLKQ is ordinary timing.
[0283] I/O circuit and buffer 406 externally provide data D1-D3,
which are provided from the second to fourth columns, via output
terminal DQ in synchronization with second to fourth pulses of
clock signal CLKQ, respectively.
[0284] According to the synchronous pseudo-SRAM of the embodiment,
as described above, since the data is output according to the
timing earlier than that defined by command latency CL, the system
side can receive the data early, and can starts the processing
early. Also, it is possible to reduce a time, for which the bus is
unfixed.
[0285] According to the embodiment, one data is output in
synchronization with first clock CLK0. However, this is not
restrictive, and two or three data may be output in synchronization
with first clock CLK0. The number of data, which are output in
synchronization with first clock CLK0, can be determined depending
on conditions or the like on the system side.
[0286] According to the embodiment, the WAIT_ASYN signal attains
"Hi-Z" in response to "H" (i.e., deactivation) of external chip
enable signal CE#. However, this is not restrictive. For example,
the WAIT_ASYN signal may attain "Hi-Z" in response to "H" of the
WAIT signal.
[0287] Number N1 of bit(s) read at first clock CLK0 may be a fixed
value, or may be set in a register by an external signal.
[0288] According to the embodiment, since number N1 of bit(s) read
at first clock CLK0 is one, one-shot pulse generator 431 is used to
produce the signal, which activates one column to be accessed in
synchronization with first clock CLK0. In the case where N1 is
larger than one, processing can be performed by adding a circuit,
which provides pulses of N1 in number formed of one-shot pulses
shifted by one cycle from each other.
[0289] The row control circuit is not restricted to that shown in
FIG. 13, and may have a structure shown in FIG. 21. Referring to
FIG. 21, delay circuits (Delay) DL191 and DL192 receive row
activating signal ACT activated in response to the rising of first
clock CLK0, i.e., clock, at which read signal READ or write signal
WRITE is produced. Delay circuit (Delay) DL191 provides sense
amplifier activating signal SENSE produced by delaying row
activating signal ACT. Delay circuit (Delay) DL192 provides column
enable signal COLE produced by delaying row activating signal
ACT.
[0290] This embodiment is not restrictively applied to the
synchronous pseudo-SRAM, and may be applied to various
semiconductor memory devices such as a flash memory operating in
synchronization with clocks. In particular, the embodiment can be
appropriately applied to the synchronous pseudo-SRAMs, which are
strongly required to achieve high packaging densities and fast
operations.
[0291] The operation example of this embodiment has been described
in connection with the case where the external signal produces read
signal READ. However, the device operates similarly when the
external signal produces write signal WRITE.
Modification of Fourth Embodiment
[0292] This modification relates to a synchronous pseudo-SRAM
operating as follows.
[0293] Even when read signal READ or write signal WRITE is produced
during the refresh operation, the burst read and write are
performed similarly to the fourth embodiment. More specifically,
several bits starting from the leading bit are read/written
according to the first clock, and the remaining bits are
read/written according to the second and following clocks defined
by command latency CL.
[0294] According to this modification, a command shift circuit 480
is added to control circuit 402 of the fourth embodiment for
dealing with the situation, in which read signal READ or write
signal WRITE is produced during the refresh operation.
[0295] FIG. 22 illustrates I/O signals of command shift circuit
480. Command shift circuit 480 receives read signal READ provided
from command decoder 410 and refresh operation signal REFRESH
provided from refresh control circuit 420, and provides a corrected
read signal READF. Corrected read signal READF is sent to the
circuits, which receive read signal READ in the foregoing
structures, instead of read signal READ.
[0296] FIG. 23 shows a specific structure of command shift circuit
480. Referring to
[0297] FIG. 23, a NAND circuit NAND81 receiving refresh operation
signal REFRESH and a NAND circuit NAND82 receiving read signal READ
form a flip-flop. An inverter IV81 inverts refresh operation signal
REFRESH.
[0298] A NAND circuit NAND83 receiving the output of inverter IV81
and a NAND circuit NAND84 receiving read signal READ form a
flip-flop.
[0299] A NAND circuit NAND85, which receives the output of NAND
circuit NAND83 and a reset signal ZPOR, and a NAND circuit NAND86
receiving outputs of NAND circuits NAND82 and NAND84 form a
flip-flop. Reset signal ZPOR becomes active to attain "H" in
response to turn-on of the power.
[0300] An inverter IV82 receives the output of NAND circuit NAND86.
An inverter IV83 receives the output of inverter IV82. A NOR
circuit NOR81 receives the outputs of NAND circuit NAND86 and
inverter IV83.
[0301] A NAND circuit NAND87 receives the outputs of NOR circuit
NOR81 and inverter IV82. Delay circuit DL81 delays the output of
NAND circuit NAND87. A NOR circuit NOR82 receives the outputs of
inverter IV83 and delay circuit DL81. Delay circuit DL82 delays the
output of NOR circuit NOR82.
[0302] A NAND circuit NAND88 receives the outputs of delay circuit
DL82 and NOR circuit NOR81. A delay circuit DL83 delays the output
of NAND circuit NAND83. A NAND circuit NAND89 receives the outputs
of delay circuit DL83 and NOR circuit NOR81.
[0303] An inverter IV84 receives the output of NAND circuit NAND89.
An inverter IV85 receives the output of inverter IV84. A NAND
circuit NAND90 receives the outputs of inverter IV85 and NAND
circuit NAND89. A NOR circuit NOR83 receives the outputs of NAND
circuit NAND90 and inverter IV84. An inverter IV86 inverts the
output of NOR circuit NOR83. An inverter IV87 inverts the output of
inverter IV86.
[0304] A NAND circuit NAND91 receives the outputs of NOR circuit
NOR83 and inverter IV87. NOR circuit NOR84 receives the outputs of
NAND circuit NAND91 and inverter IV84. An inverter IV88 inverts the
output of NOR circuit NOR84. NAND circuit NAND85 receives the
outputs of inverters IV84 and IV88. An inverter IV89 inverts the
output of NAND circuit NAND85 to provide corrected read signal
READF.
[0305] FIG. 24A illustrates corrected read signal READF appearing
when read signal READ is input while the refresh operation is not
performed. As shown in FIG. 24A, when the refresh operation is not
being performed, refresh operation signal REFRESH is at "L".
Corrected read signal READF produced by command shift circuit 480
is activated according to the same timing of as the activation of
read signal READ. Therefore, operations similar to those in the
fourth embodiment can be performed even when corrected read signal
READF is used instead of read signal READ.
[0306] FIG. 24B illustrates corrected read signal READF appearing
when read signal READ is input during the refresh operation. As
illustrated in FIG. 24B, refresh operation signal REFRESH is at "H"
when the refresh operation is being performed. When the refresh
operation ends, refresh operation signal REFRESH attains "L".
Corrected read signal READF produced by command shift circuit 480
is activated immediately after refresh operation signal REFRESH
falls and the refresh operation ends. Thereby, by using corrected
read signal READF instead of read signal READ, the operation
similar to that in the fourth embodiment can be performed
immediately after the end of the refresh. In FIG. 20, a series of
the processing starts from clock CLK0, at which read signal READ is
produced. In contrast to this, a series of the operation according
to this modification starts from the clock, at which corrected read
signal READF is input.
[0307] This modification has been described in connection with the
case where read signal READ or write signal WRITE is produced
during the refresh operation. However, the modification can be
similarly applied to the case where read signal READ or write
signal WRITE is newly produced during an operation such as read or
write operation. In particular, when the word line handled as a
target of the new reading or writing is different from the word
line, which is the target of the last reading or writing,
processing such as deactivation of the word line of the last
target, activation of the word line of the new target and
amplification by the sense amplifier is required, and therefore,
this modification is effective.
[0308] According to this modification, command shift circuit 480
produces corrected read signal READF from read signal READ.
However, this is not restrictive, and corrected write signal WRITEF
may be produced from write signal WRITE.
Fifth Embodiment
[0309] A fifth embodiment relates to a synchronous pseudo-SRAM,
which has both the synchronous mode and the asynchronous mode, and
has a preamplifier formed of a second amplifier circuit suitable
for both the modes. The sense amplifier forming the first amplifier
circuit amplifies the potentials on bit line pair BL and ZBL, and
the preamplifier forming the second amplifier circuit amplifies the
potentials on global bit line pair GIO and ZGIO connected to the
plurality of bit line pairs BL and ZBL.
[0310] (Structure)
[0311] FIG. 25 shows a structure of a synchronous pseudo-SRAM 500
according to the embodiment. Referring to FIG. 25, synchronous
pseudo-SRAM 500 includes a DRAM cell array 501, a control circuit
502, a peripheral circuit group 504 and an address buffer 503.
[0312] DRAM cell array 501 is a memory array formed of cells of a
Dynamic Random Access Memory (DRAM).
[0313] Address buffer 503 receives external address signal
ADD[21:0], and produces an internal address signal.
[0314] Control circuit 502 includes a column control circuit 505, a
command decoder 506, a shared signal producing circuit 507, a
synchronous-compatible preamplifier control circuit 508, an
asynchronous-compatible preamplifier control circuit 509, a refresh
control circuit 510 and a WAIT control circuit 511.
[0315] Column control circuit 505 provides column select signal CSL
based on the address applied thereto.
[0316] Refresh control circuit 510 controls the self-refresh
operation of the DRAM cell array based on an internal refresh timer
(not shown).
[0317] WAIT control circuit 511 keeps the WAIT signal, which is
output via a WAIT terminal, at the level of "L" while the refresh
control is being performed under the control of refresh control
circuit 510.
[0318] Command decoder 506 produces row activating signal ACT, read
signal READ and write signal WRITE according to the combination of
the logical levels of the internal control signals produced from
the external control signals.
[0319] FIG. 26 shows a structure of shared signal producing circuit
507. Referring to FIG. 26, shared signal producing circuit 507
includes a preamplifier activation preparing signal generator 523
and a synchronization instructing signal generator 524. As shown in
FIG. 26, a preamplifier activation preparing signal PAEM is
produced by delaying column select signal CSL, which is sent from
column control circuit 505, by a time of a by a delay circuit
(Delay) DL53. Preamplifier activation preparing signal PAEM is sent
to synchronous-compatible preamplifier control circuit 508 and
asynchronous-compatible preamplifier control circuit 509.
[0320] Synchronization instructing signal generator 524 includes an
inverter IV54 receiving external chip enable signal CE#, a NAND
circuit NAND53 receiving the output of inverter IV54 and external
clock CLK, an inverter IV53 receiving external chip enable signal
CE#, a delay circuit (Delay) DL51 delaying the output of inverter
IV53 by a time .beta., a NAND circuit NAND54 receiving external
chip enable signal CE# and the output of delay circuit (Delay)
DL51, a NAND circuit NAND58 receiving the outputs of NAND circuits
NAND 53 and 55, and NAND circuit NAND55 receiving the outputs of
NAND circuits NAND54 and NAND58.
[0321] FIGS. 27A and 27B are timing charts illustrating a
synchronization instructing signal SYNC.
[0322] Referring to FIG. 27A, when external clock CLK is input,
synchronization instructing signal SYNC attains "H" indicating the
synchronous mode in response to the first rising of the clock after
external chip enable signal CE# becomes active to attain "L". Then,
synchronization instructing signal SYNC attains "L" when a time of
.beta. set by delay circuit (Delay) DL51 elapses after external
chip enable signal CE# becomes inactive to attain "H".
[0323] Referring to FIG. 27B, when external clock CLK is not input,
synchronization instructing signal SYNC is at "L" indicating the
asynchronous mode.
[0324] Synchronization instructing signal SYNC is sent to
synchronous-compatible preamplifier control circuit 508 and
asynchronous-compatible preamplifier control circuit 509.
[0325] FIG. 28 shows a structure of a synchronous-compatible
preamplifier control circuit 508. As shown in FIG. 28,
synchronous-compatible preamplifier control circuit 508 includes a
reference signal generator 521 and a synchronous-compatible
preamplifier control signal generator 522 for the synchronous
operation.
[0326] FIG. 29 shows a structure of reference signal generator 521.
As shown in FIG. 29, reference signal generator 521 includes a NAND
circuit NAND56 receiving preamplifier activation preparing signal
PAEM and synchronization instructing signal SYNC, an inverter IV55
receiving the output of NAND circuit NAND56, a delay circuit
(Delay) DL52 delaying the output of inverter IV55 by a time of
.gamma., and a delay circuit (High-side Delay) HDL53 delaying the
"H" level side of output of delay circuit (Delay) DL52 by a time of
.epsilon.. The output of delay circuit (Delay) DL52 is a first
reference signal PACL, and the output of delay circuit (High-side
Delay) HDL53 is a second reference signal RAEL.
[0327] FIG. 30 shows an example of the High-side Delay. The
High-side Delay includes a P-channel MOS transistor P62, an
N-channel MOS transistor N62, a resistance R, a capacitor C51 and
an inverter IV56. A node B of the High-side delay changes from "L"
to "H" according to timing delayed from timing, according to which
a node A changes from "L" to "H". However, node B changes from "H"
to "L" according to the same timing as the change of node A from
"H" to "L".
[0328] FIG. 31 shows a structure of synchronous-compatible
preamplifier control signal generator 522. As shown in FIG. 31,
synchronous-compatible preamplifier control signal generator 522
receives first and second reference signals RAEL and PACL, and
produces an inverted preamplifier connection signal ZPADT,
preamplifier activating signal PAE, inverted preamplifier
activating signal ZPAE and an inverted preamplifier equalizing
signal ZPAEQ.
[0329] FIG. 32 illustrates timing of production of the signals
related to a synchronous-compatible preamplifier 512. Referring to
FIG. 32, when the synchronous mode is to be instructed,
synchronization instructing signal SYNC attains "H" as already
described with reference to FIG. 27A. Column select signal CSL
becomes activate to attain "H" according to appropriate timing.
[0330] Preamplifier activation preparing signal PAEM delays column
select signal CSL by the time of .alpha..
[0331] Preamplifier activation preparing signal PAEM and
synchronization instructing signal SYNC are provided to NAND
circuit NAND56 of reference signal generator 521 so that first
reference signal PACL is produced by delaying preamplifier
activation preparing signal PAEM by the time of .gamma..
[0332] Further, second reference signal PAEL, which is delayed from
the leading pulse of first reference signal PACL by the time of
.epsilon., is produced.
[0333] Synchronous-compatible preamplifier control signal generator
522 activates inverted preamplifier connection signal ZPADT to
attain "L" when first and second reference signals PACL and PAEL
are at "H" and "L", respectively. Also, synchronous-compatible
preamplifier control signal generator 522 delays second reference
signal PAEL by a time of .delta. to produce preamplifier activating
signal PAE. Further, synchronous-compatible preamplifier control
signal generator 522 inverts preamplifier activating signal PAE to
produce inverted preamplifier activating signal ZPAE and inverted
preamplifier equalizing signal ZPAEQ.
[0334] When synchronization instructing signal SYNC is at "L"
indicating the asynchronous mode, first and second reference
signals PACL and PAEL do not become active so that inverted
preamplifier connection signal ZPADT, preamplifier activating
signal PAE, inverted preamplifier activating signal ZPAE and
inverted preamplifier equalizing signal ZPAEQ do not become
active.
[0335] FIG. 33 shows a structure of asynchronous-compatible
preamplifier control circuit 509. As shown in FIG. 33,
asynchronous-compatible preamplifier control circuit 509 includes a
NAND circuit NAND57 receiving preamplifier activation preparing
signal PAEM and an inverted signal of synchronization instructing
signal SYNC, a delay circuit (Delay) DL54 delaying the output of
NAND circuit NAND57 by a time of .rho., and an inverter IV59
receiving the output of delay circuit (Delay) DL54. The output of
inverter IV59 forms preamplifier activating signal PAED.
[0336] FIG. 34 illustrates timing of production of signals related
to asynchronous-compatible preamplifier 513. Referring to FIG. 34,
when the asynchronous mode is to be instructed, synchronization
instructing signal SYNC attains "L" as illustrated in FIG. 27B.
Column select signal CSL is activated to attain "H" according to
appropriate timing.
[0337] Preamplifier activation preparing signal PAEM is produced by
delaying column select signal CSL by the time of .alpha..
[0338] Preamplifier activation preparing signal PAEM and
synchronization instructing signal SYNC are sent to
asynchronous-compatible preamplifier control circuit 509, and
preamplifier activating signal PAED is produced by delaying
preamplifier activation preparing signal PAEM by the time of
.rho..
[0339] When synchronization instructing signal SYNC is at "H"
indicating the synchronous mode, preamplifier activating signal
PAED is not activated.
[0340] Referring to FIG. 25 again, peripheral circuit group 504
includes synchronous-compatible preamplifier 512,
asynchronous-compatible preamplifier 513, a synchronous-compatible
DB driver 514, an asynchronous-compatible DB driver 516 and an
output circuit 515.
[0341] (Synchronous-Compatible Preamplifier 512)
[0342] FIG. 35 shows a structure of a synchronous-compatible
preamplifier 512. As shown in FIG. 35, synchronous-compatible
preamplifier 512 includes a switch unit 561 controlled by inverted
preamplifier connection signal ZPADT, an equalizing unit 562
controlled by inverted preamplifier equalizing signal ZPAEQ, an
amplifier unit 563 controlled by preamplifier activating signal PAE
and inverted preamplifier activating signal ZPAE, and buffer units
564 and 565 controlled by preamplifier activating signal PAE and
inverted preamplifier activating signal ZPAE.
[0343] Switch unit 561 includes P-channel MOS transistors P32 and
P31. P-channel MOS transistor P32 is arranged between global I/O
line GIO and a NODEX. P-channel MOS transistor P31 is arranged
between inverted global I/O line ZGIO and a NODEY. P-channel MOS
transistors P32 and P31 are supplied on their gates with inverted
preamplifier connection signal ZPADT.
[0344] Equalizing unit 562 includes P-channel MOS transistors P34
and P33. P-channel MOS transistor P34 is arranged between NODEX and
the power supply. P-channel MOS transistor P33 is arranged between
NODEY and the power supply. P-channel MOS transistors P34 and P33
are supplied on their gates with inverted preamplifier equalizing
signal ZPAEQ.
[0345] Amplifier unit 563 includes P-channel MOS transistors
P35-P39 and an N-channel MOS transistor N31. Between NODES and
NODET, P-channel MOS transistors P36 and P37 are arranged in
series, and P-channel MOS transistors P38 and P39 are arranged in
series and in parallel with P-channel MOS transistors P36 and P37.
P-channel MOS transistors P36 and P37 have gates connected to
NODEY. P-channel MOS transistors P38 and P39 have gates connected
to NODEX. P-channel MOS transistor P35 is arranged between the
power supply and NODES. N-channel MOS transistor N31 is arranged
between NODET and the ground. P-channel MOS transistor P35 is
supplied on its gate with inverted preamplifier activating signal
ZPAE, and N-channel MOS transistor N31 is supplies on its gate with
preamplifier activating signal PAE.
[0346] Buffer 564 includes P-channel MOS transistors P40-P42 and an
N-channel MOS transistor N32. P-channel MOS transistors P40 and P41
are arranged between the power supply and a NODEO. P-channel MOS
transistor P40 has a gate connected to NODEX. P-channel MOS
transistor P41 is supplied on its gate with preamplifier activating
signal PAE. P-channel MOS transistor P42 is arranged between NODEO
and NODEP. P-channel MOS transistor P42 receives on its gate with
inverted preamplifier activating signal ZPAE. N-channel MOS
transistor N32 is arranged between NODEP and the ground. N-channel
MOS transistor N32 has a gate connected to NODEX. Inverted
preamplifier output data ZPDD is output from NODEX.
[0347] Buffer 565 includes P-channel MOS transistors P43-P45 and an
N-channel MOS transistor N33. P-channel MOS transistors P43 and P44
are arranged between the power supply and a NODEQ. P-channel MOS
transistor P43 has a gate connected to NODEY. P-channel MOS
transistor P44 is supplied on its gate with preamplifier activating
signal PAE. P-channel MOS transistor P45 is arranged between NODEQ
and NODER. P-channel MOS transistor P45 is supplied on its gate
with inverted preamplifier activating signal ZPAE. N-channel MOS
transistor N33 is arranged between NODER and the ground. N-channel
MOS transistor N33 has a gate connected to NODEY. Preamplifier
output data PDD is output from NODEY.
[0348] Since synchronous-compatible preamplifier 512 has switch
unit 561, it can isolate global I/O line pair GIO and ZGIO from
amplifier unit 563 according to inverted preamplifier connection
signal ZPADT. Thereby, amplifier unit 563, which has taken into the
potentials on global I/O line pair GIO and ZGIO, can perform the
amplification without being affected by a change, which may occur
thereafter, and thus can perform a so-called confined amplification
so that amplifier unit 563 can perform fast amplification. Since
global I/O line pair GIO and ZGIO is isolated from amplifier unit
523, equalizing unit 562 can perform the precharge processing at
the same time as the amplification by amplifier unit 563 so that
the whole processing of the preamplifier can be performed fast.
[0349] In particular, when the read processing synchronized with
the clock is to be performed, the address changes according to
constant timing, and does not change according to random timing.
Therefore, by operating switch unit 561 to perform the isolation
according to timing not overlapping with the change in address,
data on global I/O line pair GIO and ZGIO can be handled without
missing it.
[0350] For the above reasons, it can be considered that
synchronous-compatible preamplifier 512 is suitable for the read
operation synchronized with the clock.
[0351] As described above, synchronous-compatible preamplifier 512
is not suitable for an asynchronous read operation, which is not
synchronized with the clock.
[0352] FIG. 36 is a diagram for illustrating the fact that
synchronous-compatible preamplifier 512 is not suitable for
asynchronous reading. According to the asynchronous reading, as
illustrated in FIG. 36, the read operation is performed in
accordance with change in address.
[0353] As indicated at (1) in FIG. 36, when the column address
changes after a short period from the last change in column
address, an inverted preamplifier equalizing signal ZPAQ is
activated corresponding to the respective changes, but such
activation occurs with a relatively short interval. Consequently,
the precharging cannot be performed sufficiently. Since the
amplifier is performed without precharging, distortion occurs in
output data PDD of the preamplifier as indicated at (3) in FIG. 36.
For avoiding this problem, it is necessary to keep a sufficient
precharge period before the next column access. This results in
slow processing of synchronous-compatible preamplifier 512.
[0354] As indicated at (4) in FIG. 36, when illegal address change
occurs due to noises or the like, global I/O line pair GIO and ZGIO
is supplied with the data of the column corresponding to the
illegal column address change, and then will be supplied with the
column data corresponding to the correct address change. In this
case, if global I/O line pair GIO and ZGIO is isolated from
amplifier unit 563 according to excessively early timing, illegal
data is amplified as indicated at (5) in FIG. 36, and correct data
is not amplified. For avoiding this problem, global I/O line pair
GIO and ZGIO must be isolated from amplifier unit 563 according to
delayed timing. This decreases the processing speed of
synchronous-compatible preamplifier 512.
[0355] If synchronous-compatible preamplifier 512 is used for the
asynchronous reading as described above, the processing becomes
slow. Therefore, such use is not appropriate.
[0356] (Asynchronous-Compatible Preamplifier 513)
[0357] FIG. 37 shows a structure of asynchronous-compatible
preamplifier 513. As shown in FIG. 37, this asynchronous-compatible
preamplifier 513 is an amplifier of a differential current mirror
type.
[0358] Referring to FIG. 37, P-channel MOS transistors P51 and P52
form a current mirror circuit. An N-channel MOS transistor N51 is
arranged between nodes ZPAN and NODEC. An N-channel MOS transistor
N52 is arranged between NODEE and NODED. N-channel MOS transistor
N51 has a gate connected to global I/O line GIO. N-channel MOS
transistor N52 has a gate connected to inverted global I/O line
ZGIO. A P-channel MOS transistor P53 is arranged between NODEC and
NODED. P-channel MOS transistor P53 is supplied on its gate with
preamplifier activating signal PAED.
[0359] P-channel MOS transistors P55 and P56 form a current mirror
circuit. An N-channel MOS transistor N54 is arranged between nodes
PAN and NODEG. An N-channel MOS transistor N53 is arranged between
NODEF and NODEG. N-channel MOS transistor N54 has a gate connected
to inverted global I/O line ZGIO. N-channel MOS transistor N53 has
a gate connected to global I/O line GIO. A P-channel MOS transistor
P57 is arranged between NODEG and NODEH. P-channel MOS transistor
P57 is supplied on its gate with preamplifier activating signal
PAED.
[0360] An N-channel MOS transistor N55 is arranged between NODED
and the ground. N-channel MOS transistor N55 is supplied on its
gate with preamplifier activating signal PAED. A P-channel MOS
transistor P54 is arranged between NODEE and NODEF. P-channel MOS
transistor P54 is supplied on its gate with preamplifier activating
signal PAED.
[0361] P-channel MOS transistors P58 and P59 are arranged in
parallel between the power supply and a node ZPAN2. P-channel MOS
transistor P58 receives preamplifier activating signal PAED on its
gate, and P-channel MOS transistor P59 has a gate connected to node
PAN.
[0362] Between node ZPAN2 and the ground, N-channel MOS transistors
N56, N57 and N58 are connected in series. N-channel MOS transistor
N56 has a gate connected to inverted global I/O line ZGIO.
N-channel MOS transistor N57 has a gate connected to a node PAN2.
N-channel MOS transistor N58 is supplied on its gate with
preamplifier activating signal PAED.
[0363] Further, P-channel MOS transistors P60 and P61 are arranged
in parallel between the power supply and node PAN2. P-channel MOS
transistor P61 is supplied on its gate with preamplifier activating
signal PAED. P-channel MOS transistor P60 has a gate connected to
node ZPAN.
[0364] N-channel MOS transistors N59, N60 and N61 are connected in
series between node PAN2 and the ground. N-channel MOS transistor
N59 has a gate connected to inverted global I/O line ZGIO.
N-channel MOS transistor N60 has a gate connected to node ZPAN2.
N-channel MOS transistor N61 is supplied on its gate with
preamplifier activating signal PAED.
[0365] A NOR circuit NOR99 connected to node PAN2 and a NOR circuit
NOR98 connected to node ZPAN2 form a flip-flop. An inverter IV51
inverts the output of NOR circuit NOR99 to provide a preamplifier
output signal PAN3. An inverter IV52 inverts the output of NOR
circuit NOR98 to output an inverted preamplifier output signal
ZPAN3.
[0366] FIG. 38 illustrates changes of potentials on various nodes
of asynchronous-compatible preamplifier 513 over time.
[0367] Asynchronous-compatible preamplifier 513 does not have a
switch unit in contrast to synchronous-compatible preamplifier 512,
and is a preamplifier of a non-confined type. Therefore,
asynchronous-compatible preamplifier 513 is not isolated from
global I/O lines GIO and ZGIO during amplification, and therefore
is suitable for asynchronous reading, which is performed according
to change in address.
[0368] Referring to FIG. 25 again, synchronous-compatible DB driver
514 provides the potential received thereby onto a data bus DB.
FIG. 39 shows a structure of synchronous-compatible DB driver 514.
As shown in FIG. 39, synchronous-compatible DB driver 514 is formed
of an inverter IV74, which receives an output PDD of
synchronous-compatible preamplifier 512, and inverts it to provide
the inverted output onto data bus DB.
[0369] Asynchronous-compatible DB driver 516 provides the received
potential onto data bus DB. FIG. 40 shows a structure of
asynchronous-compatible DB driver 516. Asynchronous-compatible DB
driver 516 is formed of an inverter IV72, which receives and
inverts an output PAN3 of asynchronous-compatible preamplifier 513
to provide the inverted output onto data bus DB.
[0370] Output circuit 515 in FIG. 25 receives data from data bus
DB, and externally provides the data via data output terminal
DQ.
[0371] As described above, since the synchronous pseudo-SRAM
according to the embodiment has the preamplifier operating
appropriately in the synchronous mode as well as the preamplifier
operating appropriately in the asynchronous mode, the potential
difference on global I/O line pair GIO and ZGIO can be correctly
amplified in all the modes.
[0372] In this embodiment, the different preamplifiers are employed
for the synchronous operation and the asynchronous operation,
respectively. However, this is not restrictive, and different
preamplifiers may be employed for the burst mode and the random
access, respectively. In this case, the semiconductor memory device
does not have the synchronous mode and the asynchronous mode, but
has the burst mode and the random access mode. For the burst mode,
a preamplifier such as preamplifier 512, which can perform the
confined-type amplification, is suitable so that a pre-read
operation and a pipeline operation can be executed efficiently.
[0373] According to the embodiment, synchronization instructing
signal SYNC switches the mode between the synchronous and
asynchronous modes. However, this is not restrictive, and a bonding
option PAD may be employed such that a potential applied thereto
can switch the mode between the synchronous and asynchronous
modes.
[0374] Although the embodiment employs synchronous-compatible DB
driver 514 and asynchronous-compatible DB driver 516, a DB driver
corresponding to the synchronous and asynchronous modes may be
used.
[0375] FIG. 41 shows a structure of a shared DB driver 590 serving
as both synchronous- and asynchronous-compatible DB drivers 514 and
516. As shown in FIG. 41, shared DB driver 590 is formed of a NOR
circuit NOR71, which receives output PDD of synchronous-compatible
preamplifier 512 and output PAN3 of asynchronous-compatible
preamplifier 513, and an inverter IV73 inverting the output of NOR
circuit NOR71 and providing the inverted output onto data bus
DB.
[0376] FIG. 42 shows a layout of synchronous- and
asynchronous-compatible preamplifiers 512 and 513. As shown in FIG.
42, synchronous-compatible preamplifiers 512 are arranged in a
synchronous-compatible preamplifier arrangement region 596, and
asynchronous-compatible preamplifiers 513 are arranged in an
asynchronous-compatible preamplifier arrangement region 597.
[0377] Synchronous- and asynchronous-compatible preamplifiers 512
and 513 connected to the same global I/O line pair GIO and ZGIO are
aligned in the column direction. An arrangement layer of global I/O
line pair GIO and ZGIO is different from an arrangement layer of
the preamplifiers, and global I/O line pair GIO and ZGIO does not
have a diverging point, and connects synchronous- and
asynchronous-compatible preamplifiers 512 and 513 together.
[0378] According to the layout shown in FIG. 42, as described
above, it is not necessary to diverge global I/O line pair GIO and
ZGIO, which facilitates the arrangement of global I/O line pair GIO
and ZGIO. This layout is suitable for the case where synchronous
pseudo-SRAM 500 can have a large size in the column direction.
[0379] FIG. 43 shows another layout of synchronous-compatible
preamplifiers 512 and asynchronous-compatible preamplifiers 513. As
shown in FIG. 43, synchronous-compatible preamplifiers 512 and
asynchronous-compatible preamplifiers 513 are arranged in a
synchronous/asynchronous-compatible preamplifier arrangement region
598.
[0380] Synchronous- and asynchronous-compatible preamplifiers 512
and 513 connected to each global I/O line pair GIO and ZGIO are
aligned in the row direction. Global I/O line pair GIO and ZGIO has
diverged portions, which are connected to synchronous- and
asynchronous-compatible preamplifiers 512 and 513,
respectively.
[0381] According to the layout shown in FIG. 43, as described
above, global I/O line pair GIO and ZGIO must be diverged. This
layout is suitable for the synchronous pseudo-SRAM 500, which can
have a large size in the row direction.
Sixth Embodiment
[0382] A sixth embodiment relates to a synchronous pseudo-SRAM
having a byte mask function. In this synchronous pseudo-SRAM, a
higher byte or a lower byte may be masked making it possible to
prohibit external output of data read from memory cells. The burst
mode contains a no-wrap mode. According to the no-wrap mode, when
the last column is processed during the course of the burst reading
or writing, a next row is then processed. In this case, it is
necessary to perform deactivation of the word line already
selected, activation of the word line to be newly selected and row
access processing such as amplifying processing by the sense
amplifier. While the row access processing is being performed, the
WAIT signal is externally output. A byte mask signal can be applied
from the external system side after this WAIT signal is released.
For some systems, however, it is desired to allow setting of the
byte mask in the same method, regardless of whether row access
processing for changing to the next row is performed or not. This
embodiment provides the synchronous pseudo-SRAM, which allows
external application of the byte mask signal in the same manner as
the case of not effecting the burst reading or burst writing over
two rows, even when the burst reading or burst writing is to be
effected over two rows, i.e., first and second rows, and the
processing target changes to the second row after processing is
effected on the last column in the first row during the course of
the processing.
[0383] (Structure)
[0384] FIG. 44 shows a structure of a synchronous pseudo-SRAM 600
according to this embodiment. Referring to FIG. 44, synchronous
pseudo-SRAM 600 includes a DRAM cell array 601, a CLK buffer 604, a
UB buffer 605, an LB buffer 606, a WE buffer 607, an ADV buffer
608, a control circuit 602, a peripheral circuit group 603 and a
BCR (Bus Configuration Register) 610.
[0385] DRAM cell array 601 is a memory array formed of cells of a
Dynamic Random Access Memory (DRAM).
[0386] Peripheral circuit group 603 includes global I/O line pair
GIOP (GIO and /GIO), which is not shown, as well as column select
lines provided corresponding to the respective columns, column
select gates, sense amplifiers, preamplifiers, a write driver, a
row decoder, a column decoder and others. Peripheral circuit group
603 further includes an output circuit 620.
[0387] Output circuit 620 holds data provided from DRAM cell array
601. Output circuit 620 receives an output enable signal OE for
higher bytes as well as output enable signal OE for lower bytes.
When output enable signal OE for the higher bytes is at "H"
indicating "Enable", output circuit 620 externally provides the
higher bytes in the held data via data I/O terminal DQ. When output
enable signal OE for the lower bytes is at "H" indicating "Enable",
output circuit 620 externally provides the lower bytes in the held
data via data I/O terminal DQ.
[0388] BCR 610 stores an interface to the external system such as
burst length BL and command latency CL.
[0389] FIG. 45 shows a specific structure of a CE buffer 609.
Referring to FIG. 45, a CE buffer 608 includes an inverter 1 formed
of P- and N-channel MOS transistors P71 and N71 receiving external
chip enable signal CE#, an inverter 2 formed of P- and N-channel
MOS transistors P72 and N72 connected to inverter 1, and an
inverter 3 formed of P- and N-channel MOS transistors P73 and N73
connected to inverter 2. The output of inverter 2 forms an inverted
internal chip enable signal ZINTCE, and the output of inverter 3
forms an internal chip enable signal INTCE.
[0390] FIG. 46 shows a specific structure of UB buffer 605.
Referring to FIG. 46, UB buffer 605 includes an inverter 1 formed
of P- and N-channel MOS transistors P75 and N74 receiving an
external high byte mask signal UB#, an inverter 2 formed of P- and
N-channel MOS transistors P76 and N76 connected to inverter 1, and
an inverter IV44 connected to inverter 2. The output of inverter
IV44 forms an internal higher byte mask signal INTUB. Further, a
P-channel MOS transistor P74 is arranged between the power supply
and P-channel MOS transistor P75. An N-channel MOS transistor N75
is arranged between a connection node, which is formed between
inverters 1 and 2, and the ground.
[0391] Gates of P- and N-channel MOS transistors P74 and N75
receive inverted internal chip enable signal ZINTCE. When the chip
is active, inverted internal chip enable signal ZINTCE attains "L".
In this state, P-channel MOS transistor P75 is connected to the
power supply, and the connection node between inverters 1 and 2 is
not grounded. Therefore, a normal operation is performed.
[0392] When the chip is inactive, inverted internal chip enable
signal ZINTCE attains "H". In this state, P-channel MOS transistor
P75 is isolated from the power supply, and the connection node
between inverters 1 and 2 is grounded. Therefore, internal higher
byte mask signal INTUB is always at "L".
[0393] Other input buffers, i.e., CLK buffer 604, LB buffer 606, WE
buffer 607 and ADV buffer 608 have the same structures as UB buffer
605, and therefore description thereof is not repeated.
[0394] Referring to FIG. 44 again, control circuit 602 includes a
command decoder 611, a ZRST producing circuit 612, a ZUB0 producing
circuit 613, a ZLB0 producing circuit 614, an ADV0 producing
circuit 615, a ZWE0 producing circuit 616, a mask control circuit
617, a row control circuit 618, a WAIT control circuit 619 and a
refresh control circuit 621.
[0395] Command decoder 611 produces row activating signal ACT and
read signal READ according to the combination of the logical levels
of the internal control signals produced from the external control
signals.
[0396] FIG. 47 shows a specific structure of ZUB0 producing circuit
613. Referring to FIG. 47, a clocked inverter CIV61 receives
internal higher byte mask signal INTUB. Clocked inverter CIV61
provides its output to a bistable circuit formed of inverters IV21
and IV22. The bistable circuit provides its output to an inverter
IV23. The output of inverter IV23 and an internal clock INTCLK are
sent to a NAND circuit NAND21. NAND circuit NAND21 provides its
output to an inverter IV24, and the output of inverter IV24 forms
ZUB0.
[0397] FIG. 48 shows a specific structure of ZLB0 producing circuit
614. Referring to FIG. 48, a clocked inverter CIV62 receives
internal lower byte mask signal INTLB. Clocked inverter CIV62
provides its output to a bistable circuit formed of inverters IV25
and IV26. The bistable circuit provides its output to an inverter
IV27. The output of inverter IV27 and internal clock INTCLK are
provided to a NAND circuit NAND22. NAND circuit NAND22 provides its
output to an inverter IV28, of which output forms ZLB0.
[0398] FIG. 49 shows a specific structure of ADV0 producing circuit
615. Referring to FIG. 49, a clocked inverter CIV63 receives an
internal address take-in signal INTADV. Clocked inverter CIV63
provides its output to a bistable circuit formed of inverters IV29
and IV30. The output of the bistable circuit and internal clock
INTCLK are provided to a NAND circuit NAND23. The output of NAND
circuit NAND23 is sent to an inverter IV31, of which output forms
ADV0. The output of the bistable circuit is sent to an inverter
IV32. The output of inverter IV32 and internal clock INTCLK are
sent to a NAND circuit NAND24. The output of NAND circuit NAND24 is
sent to an inverter IV33, of which output forms ZADV0.
[0399] FIG. 50 shows a specific structure of ZWE0 producing circuit
616. Referring to FIG. 50, a clocked inverter CIV64 receives an
internal write enable signal INTWE. Clocked inverter CIV64 provides
its output to a bistable circuit formed of inverters IV34 and IV35.
The output of the bistable circuit is sent to an inverter IV36. The
output of inverter IV36 and internal clock INTCLK are sent to NAND
circuit NAND25. NAND circuit NAND25 provides its output to an
inverter IV37, of which output forms ZWE0.
[0400] FIG. 51 shows a specific structure of ZRST producing circuit
612. Referring to FIG. 51, an inverter IV38 receives read signal
READ. A delay circuit (Delay) DL99 delays an output of an inverter
IV99. A NOR circuit NOR21 receives read signal READ and the output
of delay circuit (Delay) DL99. An inverter IV42 receives the output
of NOR circuit NOR21. The output of inverter IV42 forms an inverted
reset signal ZRST.
[0401] FIG. 52 illustrates timing of production of inverted reset
signal ZRST. AS shown in FIG. 52, inverted reset signal ZRST is
activated to become a pulse at "L" level when read signal READ is
deactivated to attain "L".
[0402] FIG. 53 shows a specific structure of mask control circuit
617. Although FIG. 53 shows only a lower side (LB), an upper side
(UB) have substantially the same structure. Referring to FIG. 53, a
NAND circuit NAND26 in a first control circuit 631 receives ADV0,
ZLB0 and ZWE0. NAND circuits NAND29 and NAND30 form a flip-flop.
NAND circuit NAND29 receives the output of NAND circuit NAND26.
NAND circuit NAND30 receives inverted reset signal ZRST. An
inverter IV39 receives the output of NAND circuit NAND29. The
output of inverter IV39 forms a first output enable signal OE1.
According to this structure, if an external byte mask signal LB#
indicates that the byte mask is to be effected on the leading bit
in the burst access, first control circuit 631 keeps first output
enable signal OE1 at "L" from clock CLK, at which external byte
mask signal LB# attains "H", to the point in time including the
timing of output of the leading bit from output circuit 620.
[0403] In a second control circuit 632, a NAND circuit NAND27
receives ZADV0, ZLB0 and ZWE0. NAND circuits NAND31 and NAND32 form
a flip-flop. NAND circuit NAND31 receives the output of NAND
circuit NAND27. NAND circuit NAND31 receives inverted reset signal
ZRST. A NAND circuit NAND35 receives a ZWAIT signal and the output
of NAND circuit NAND31. The output of NAND circuit NAND35 forms a
second output enable signal OE2. According to this structure, a
second control circuit 632 operates as follows in the case where
external byte mask signal LB# indicates that the byte mask is to be
effected on the bit other than the leading bit, and the row access
processing is not performed for change to a next row. In the above
case, if the WAIT signal is at "H" when the bit in question is to
be output to output circuit 620, second control circuit 632 sets
second output enable signal OE2 to "L", as is usually done. If WAIT
signal is at "L", second control circuit 632 does not set second
output enable signal OE2 to "L", and provides a signal produced
based on the byte mask signal (i.e., the output of NAND circuit
NAND27) to a third control circuit 633.
[0404] In third control circuit 633, an inverter IV41 receives the
ZWAIT signal. A delay circuit (Delay) DL21 delays the output of
inverter IV41. A NAND circuit NAND28 receives the ZWAIT signal and
the output of delay circuit (Delay) DL21. NAND circuits NAND33 and
NAND34 form a flip-flop. NAND circuit NAND33 receives the output of
NAND circuit NAND27. NAND circuit NAND34 receives inverted reset
signal ZRST and the output of NAND circuit NAND28. An inverter IV40
receives the ZWAIT signal. A NAND circuit NAND36 receives the
output of inverter IV40 and the output of NAND circuit NAND33. The
output of NAND circuit NAND36 forms a third output enable signal
OE3. According to the above structure, third control circuit 633
receives and holds a signal produced based on the byte mask signal.
When the WAIT signal changes from "L" to "H", third control circuit
633 changes third output enable signal OE3 to "L".
[0405] A NAND circuit NAND60 receives first, second and third
output enable signals OE1, OE2 and OE3. An inverter IV43 receives
the output of NAND circuit NAND60, and provides output enable
signal OE. NAND circuit NAND60 and inverter IV43 set output enable
signal OE to "L" when at least one of first, second and third
output enable signals OE1, OE2 and OE3 is at "L".
[0406] Referring to FIG. 44 again, row control circuit 618 controls
the row access processing such as activation of the word line and
amplification by the sense amplifier.
[0407] Refresh control circuit 621 controls the self-refresh
operation of the DRAM cell array based on an internal refresh timer
(not shown).
[0408] During the refresh control by refresh control circuit 621,
and during the course of the burst reading in the no-wrap mode, the
row access processing (deactivation of the word line in the last
row, activation of the word line in the new row, and amplification
by the sense amplifier) is performed for change to the next row
after the processing is effected on the last column. In this case,
WAIT control circuit 619 sets the level of the WAIT signal, which
is to be output via the WAIT terminal, to "L". Thus, the WAIT
signal set to "L" externally notifies that a waiting state is kept
until the output of data.
[0409] (Access Operation without Change to the Next Row)
[0410] FIG. 54 is a timing chart illustrating changes in signal,
which occur when change to the next row is not performed during the
burst reading in synchronous pseudo-SRAM 600 according to the
embodiment. Referring to FIG. 54, examples 1-3 of the operation
will now be described.
Example 1
Masking is not Performed
[0411] External byte mask signals LB# and UB# do not attain "H" in
any case. In this case, first, second and third output enable
signals OE1, OE2 and OE3 are at "H" over the whole period.
Example 2
Second Bit is Masked
[0412] External byte mask signals LB# and UB# are at "H" during (1)
in FIG. 54. In this case, first and third output enable signals OE1
and OE3 are at "H" over the whole period. As indicated at (2) in
FIG. 54, second output enable signal OE2 is at "L" according to
timing of output the second bit from output circuit 620 (i.e., from
rising of clock CLK3 to rising of clock CLK4).
Example 3
First Bit is Masked
[0413] External byte mask signals LB# and UB# are at "H" during (3)
in FIG. 54. In this case, second and third output enable signals
OE2 and OE3 are at "H" over the whole period. As indicated at (4)
in FIG. 54, first output enable signal OE1 is at "L" from clock
CLK, at which external byte mask signals LB# and UB# attain "H", to
the point in time of output of the first bit from output circuit
620 (i.e., from rising of clock CLK0 to rising of clock CLK3).
[0414] (Access Operation Accompanied with Change to the Next Row in
the No-Wrap Mode)
[0415] FIG. 55 is a timing chart illustrating changes in the case
where change to the next row is performed in the burst reading when
synchronous pseudo-SRAM 600 of this embodiment is in the no-wrap
mode. Referring to FIG. 55, examples 1-3 of the operations will now
be described.
Example 1
Masking is not Performed
[0416] External byte mask signals LB# and UB# do not attain "H".
First, second and third output enable signals OE1, OE2 and OE3 are
at "H" over the whole period.
Example 2
Second Bit is Masked, and Change to Next Row is Performed
[0417] External byte mask signals LB# and UB# are at "H" during (1)
in FIG. 55. In this case, first and second output enable signals
OE1 and OE2 are at "H" over the whole period. As indicated at (3)
in FIG. 55, third output enable signal OE3 is at "L" according to
timing of the operation, in which the WAIT signal attains "H"
(i.e., from rising of a clock CLK7 to rising of a clock CLK8).
[0418] Thereby, the processing of masking the second bit is
deferred until the WAIT signal attains "H" after the end of the
processing of accessing the next row.
Example 3
Third Bit is Masked
[0419] External byte mask signals LB# and UB# are at "H" during (3)
in FIG. 55. In this case, first and third output enable signals OE1
and OE3 at "H" over the whole period. As indicated at (4) in FIG.
55, second output enable signal OE1 is at "L" according to timing
of output of the third bit from output circuit 620 (i.e., from
rising of clock CLK8 to rising of clock CLK9).
Example 4
First Bit is Masked
[0420] Although not illustrated in the drawings, the signals change
in the same manner as the example 3 in FIG. 54.
[0421] As is apparent from the above description, the timing of
setting the byte mask signal of the second bit, i.e., the timing of
applying external byte mask signals LB# and UB# is the timing
indicated at (A) in FIG. 54 or 55. Therefore, even in the case of
changing to the next row during the burst reading or burst writing,
it is possible to apply externally the byte mask signal in the
substantially same manner as the case where change to the next row
is not performed.
[0422] This embodiment can be applied not only to the no-wrap mode,
but can also be effectively applied to a continuous mode, in which
read/write is continuously performed until the chip enable signal
becomes inactive.
[0423] This embodiment is not restrictively applied to the
synchronous pseudo-SRAM, and may be applied to various
semiconductor memory devices operating in synchronization with
clocks.
Seventh Embodiment
[0424] A seventh embodiment relates to a dual-purpose
mobile/cellular RAM 700 having both functions of a mobile RAM and
the cellular RAM. The cellular RAM is a synchronous pseudo-SRAM
disclosed in the foregoing reference "CellularRAM.RTM. Memory". The
mobile RAM is a synchronous pseudo-SRAM having a function peculiar
to a cellular phone.
[0425] (Structure)
[0426] FIG. 56 shows a structure of a dual-purpose mobile/cellular
RAM 700 of this embodiment. Referring to FIG. 56, dual-purpose
mobile/cellular RAM 700 includes a DRAM cell array 701, a control
circuit 707 and an I/O circuit 705.
[0427] DRAM cell array 701 is a memory array formed of cells of a
Dynamic Random Access Memory (DRAM).
[0428] I/O circuit 705 receives externally applied data via data
output terminal DQ, and externally provides data.
[0429] Control circuit 707 includes a shared unit 702, a mobile RAM
dedicated unit 703, a cellular RAM dedicated unit 704, and a
mobile-RAM/cellular RAM determining circuit 706.
[0430] Mobile-RAM/cellular RAM determining circuit 706 determines,
according to the external signals, the unit to be operated among
shared unit 702, mobile RAM dedicated unit 703 and cellular RAM
dedicated unit 704, and operates it.
[0431] Shared unit 702 executes the functions to be executed in
both the mobile RAM and the cellular RAM.
[0432] Mobile RAM dedicated unit 703 executes the function to be
executed only by the mobile RAM.
[0433] Cellular RAM dedicated unit 704 executes the function to be
executed only by the cellular RAM.
[0434] FIG. 57 illustrates a structure of shared unit 702. As
illustrated in FIG. 57, shared unit 702 includes a refresh timer
721, a sense operation control circuit 722, an address anti-skew
circuit 723 and an I/O buffer 724.
[0435] Refresh timer 721 provides a timing signal for performing
the self-refresh.
[0436] Sense operation control circuit 722 controls the operation
of the sense amplifier.
[0437] Address anti-skew circuit 723 performs control to prevent
address skew.
[0438] I/O buffer 724 receives and holds the external control
signals, external address signals and external clocks, and produces
the internal control signals, internal address signals and internal
clocks. Also, I/O buffer 724 holds the data to be externally
output.
[0439] FIG. 58 illustrates a structure of a cellular RAM dedicated
unit 704. As illustrated in FIG. 58, cellular RAM dedicated unit
704 includes a synchronous interface circuit 741, a ZADV control
circuit 742, a NOR interface circuit 743, an additional
Cellular-compatible operation control circuit 744 for control of
other operations, and a BCR/RCR set circuit 745.
[0440] Synchronous interface circuit 741 controls operations
synchronized with the clock.
[0441] ZADV control circuit 742 controls an operation of taking in
the external address based on external address take-in signal
ADV#.
[0442] NOR interface circuit 743 controls an interface to a
NOR-type flash memory,
[0443] Additional Cellular-compatible operation control circuit 744
controls, e.g., an SRAM-compatible interface.
[0444] BCR/RCR set circuit 745 sets BCR and RCR.
[0445] FIG. 59 illustrates a structure of a mobile RAM dedicated
unit 703. As illustrated in FIG. 59, mobile RAM dedicated unit 703
includes a command mode circuit 731, a burst refresh circuit 732,
an early write circuit 733 and a data holding block control circuit
734.
[0446] Command mode circuit 731 sets and resets internal registers
according to a combination of external signals.
[0447] Burst refresh circuit 732 holds a refresh request in an
internal counter, and will continuously perform the refresh
operation in response to application of certain constant
timing.
[0448] Early write circuit 733 controls an early write operation,
i.e., the write operation to be performed according to early
timing.
[0449] Data holding block control circuit 734 performs the control
to refresh only the selected block, and thereby holds only the data
in the selected block.
[0450] As described above, since the RAM according to this
embodiment is configured to achieve efficiently both the functions
of the cellular RAM and the mobile RAM, production management can
be performed efficiently, and inventories can be reduced at the
time of changeover of products. Also, it is possible to reduce a
development cost.
Eighth Embodiment
[0451] An eighth embodiment relates to a synchronous pseudo-SRAM,
which uses a burst length counter for executing precharging.
[0452] (Structure)
[0453] FIG. 60 shows a structure of a synchronous pseudo-SRAM 800
according to the embodiment. Referring to FIG. 60, synchronous
pseudo-SRAM 800 includes a DRAM cell array and peripheral circuit
group 801, a control circuit 802, a command decoder 803, a BCR
(Burst Configuration Register) 804 and a burst length counter
805.
[0454] The DRAM cell array in DRAM cell array and peripheral
circuit group 801 is a memory array formed of cells of a Dynamic
Random Access Memory (DRAM). The peripheral circuit group includes
global I/O line pair GIOP (GIO and /GIO) as well as column select
lines provided corresponding to the respective columns, column
select gates, sense amplifiers, preamplifiers, a write driver, a
row decoder, a column decoder and others.
[0455] Command decoder 803 produces row activating signal ACT, read
signal READ and write signal WRITE according to the combination of
the logical levels of the internal control signals produced from
the external control signals.
[0456] BCR 804 stores an interface to the external system such as
burst length BL, command latency CL and others.
[0457] FIG. 61 shows a specific structure of burst length counter
805. Referring to FIG. 61, burst length counter 805 includes a CSL
counter 999 and an AND circuit AND101. CSL counter 999 receives
column select signal CSL. When CSL counter 999 counts the pulses of
column select signal CSL, which are equal in number to the value of
burst length BL, it provides "H". AND circuit AND101 receives
external clock CLK and the output of CSL counter 999, and activates
a burst length reset signal BLRST to attain "H" according to timing
of first input of clock CLK after the output of CSL counter 999
attains "H".
[0458] Control circuit 802 includes a row control circuit 806. When
row control circuit 806 receives burst length reset signal BLRST,
it activates a precharge signal PRC. This precharge signal PRC
deactivates the word line, and precharges the bit line pair.
[0459] (Operation)
[0460] FIG. 62 is a timing chart illustrating deactivation of the
word line. As illustrated in FIG. 62, when read signal READ and
write signal WRITE are received at clock CLK0, and column select
signal CSL for selecting the last column in the burst access
becomes active at clock CLK CLK4 owing to command latency CL equal
to 2 and burst length BL equal to 4. Burst length counter 805
activates burst length reset signal BLRST to attain "H" at clock
CLK5, i.e., fifth clock corresponding to (CL+BL-1=5) after clock
CLK0. Based on this burst length reset signal BLRST, precharge
signal PRC is activated so that the selected word line (X.sub.0) is
deactivated, and the bit line pair is precharged.
[0461] According to the synchronous pseudo-SRAM of the embodiment,
as described above, when burst length counter 805 counts the pulses
of column select signal CSL, which are equal in number to the value
of burst length BL, it activates burst length reset signal BLRST so
that the word line can be deactivated without returning external
chip enable signal CE# to "H".
[0462] According to the synchronous pseudo-SRAM of the embodiment,
as described above, the word line is not deactivated according to
external control, but is deactivated according to internal control
so that the control can be simple.
[0463] Such a manner may be employed that the reset signal is
generated in response to the falling of external address take-in
signal ADV#, and precharge signal PRC may be generated in response
to this reset signal.
[0464] According to this embodiment, although the word line is
deactivated based on burst length reset signal BLRST, this is not
restrictive. For example, a standby state, in which neither reading
nor writing is performed, may be attained based on burst length
reset signal BLRST.
[0465] This embodiment is not restrictively applied to the
synchronous pseudo-SRAM, and may be applied to various
semiconductor memory devices operating in synchronization with
clocks.
Ninth Embodiment
[0466] A ninth embodiment relates to a synchronous pseudo-SRAM
having a mode, in which a synchronous mode is fixed.
[0467] (Setting of Synchronous/Asynchronous Mode in the Background
Art)
[0468] First, description will be given on setting of
synchronous/asynchronous mode of the CellularRAM.RTM. in the
background art.
[0469] FIG. 63 illustrates a manner of setting the
synchronous/asynchronous mode in the background art. As illustrated
in FIG. 63, when tCSP is equal to or greater than 20 ns, the
asynchronous-fixed mode is set regardless of a value of BCR[15],
which is a 15th bit in the BCR (Bus Configuration Register). When
tCSP is smaller than 20 ns, the mode is set depending on the value
of BCR[15]. tCSP is a time from the falling of external chip enable
signal CE# to the rising of external clock CLK.
[0470] FIGS. 64A and 64B illustrate the setting of the modes
according to the value of tCSP. In FIG. 64A, tCSP is 7.5 ns. In
this case, since tCSP is smaller than 20 ns, reference is made to
the value of BCR[15]. When the value is zero,
synchronous/asynchronous mixed mode is set. When the value is one,
asynchronous-fixed mode is set.
[0471] In FIG. 64B, tCSP is 22.5 ns. In this case, tCSP is equal to
or greater than 20 ns. Therefore, when 20 ns elapses from the
falling of external clock CLK, asynchronous-fixed mode is set.
[0472] As is apparent from the above description and FIG. 64B, when
the clock frequency is low, the asynchronous-fixed mode is forcedly
set. Therefore, the operation in the synchronous mode cannot be
performed with a low clock frequency.
[0473] Therefore, the embodiment provides the synchronous
pseudo-SRAM, which can be set to the synchronous mode even when
tCSP is equal to or smaller than 20 ns, and thus, even when the
clock frequency is low.
[0474] (Setting of Synchronous/Asynchronous Mode of the
Embodiment)
[0475] FIG. 65 illustrates a manner of setting the
synchronous/asynchronous mode in this embodiment. As illustrated in
FIG. 65, when the value of BCR[16] is zero, the synchronous-fixed
mode is set regardless of the values of tCSP and BCR[15]. When the
value of BCR[16] is one, the mode is set similarly to the
conventional manner depending on the values of tCSP and
BCR[15].
[0476] (Structure)
[0477] FIG. 66 shows a structure of a synchronous pseudo-SRAM 900
according to the embodiment. Referring to FIG. 66, synchronous
pseudo-SRAM 900 includes a DRAM cell array and peripheral circuit
group 901, a BCR (Bus Configuration Register) 903, a tCSP
determining circuit 906, a synchronous control circuit 904, an
asynchronous control circuit 905 and a shared control circuit
902.
[0478] The DRAM cell array in DRAM cell array and peripheral
circuit group 901 is a memory array formed of cells of a Dynamic
Random Access Memory (DRAM). The peripheral circuit group includes
global I/O line pair GIOP (GIO and /GIO) as well as column select
lines provided corresponding to the respective columns, column
select gates, sense amplifiers, preamplifiers, a write driver, a
row decoder, a column decoder and others.
[0479] BCR 903 defines an interface to the external system.
[0480] tCSP determining circuit 906 asserts asynchronous control
signal ASYNTRG when a time of 20 ns or greater elapses from the
falling of external chip enable signal CE# to the rising of
external clock CLK. tCSP determining circuit 906 receiving BCR[15]
and BCR[16] does not perform the processing of determining tCSP
when BCR[15] is equal to one, or BCR[16] is equal to zero. In these
cases, it is not necessary to determine tCSP because the
synchronous-fixed mode is set when BCR[16] is equal to zero, and
the asynchronous-fixed mode is set when BCR[16] is equal to one and
BCR[15] is equal to one.
[0481] Synchronous control circuit 904 receives BCR[16],
asynchronous control signal ASYNTRG and BCR[15], and becomes active
when the combination of them indicates the synchronous-fixed mode
or the synchronous/asynchronous-mixed mode illustrated in FIG. 65.
More specifically, when BCR[16] is equal to zero, or when BCR[16]
is equal to one, asynchronous control signal ASYNTRG is inactive
and BCR[15] is equal to zero, synchronous control circuit 904
becomes active. In other cases, synchronous control circuit 904
becomes inactive. When synchronous control circuit 904 is active,
it controls the operations of synchronous pseudo-SRAM 900
synchronized with external clock CLK.
[0482] Asynchronous control circuit 905 receives BCR[16],
asynchronous control signal ASYNTRG and BCR[15], and becomes active
when the combination of them indicates the synchronous/asynchronous
mixed mode illustrated in FIG. 65. In the cases, it becomes
inactive. More specifically, when BCR[16] is equal to one,
asynchronous control circuit 905 becomes active. When BCR[16] is
equal to zero, asynchronous control circuit 905 becomes inactive.
When it is active, asynchronous control circuit 905 controls the
operations not synchronized with external clock CLK of synchronous
pseudo-SRAM 900.
[0483] Shared control circuit 902 controls operations independent
of synchronization and non-synchronization with external clock
CLK.
[0484] According to the synchronous pseudo-SRAM of the embodiment,
as described above, the synchronous-fixed mode can be set
independently of the value of tCSP so that the operation
synchronized with the clock can be performed even with a low clock
frequency.
[0485] According to the embodiment, the synchronous/asynchronous
modes are set by using neighboring bits such as BCR[15] and
BCR[16], this facilitates the circuit connection.
[0486] According to this embodiment, the synchronous-fixed mode is
set according to the value of BCR[16]. However, this is not
restrictive. For example, the synchronous-fixed mode may be set
according to, e.g., another bit of BCR, a bit of another register,
a bonding option or an external signal.
[0487] This embodiment is not restrictively applied to the
synchronous pseudo-SRAM, and may be applied to various
semiconductor memory devices having the synchronous mode for
operation in synchronization with a clock and an asynchronous mode
for operation asynchronous to the clock.
Tenth Embodiment
[0488] A tenth embodiment relates to a synchronous pseudo-SRAM,
which uses external chip enable signal CE# for controlling
activation/deactivation of the input buffer, and avoids a problem,
which may arise when external chip enable signal CE# is activated
without synchronization with the clock.
[0489] (Structure)
[0490] FIG. 67 shows a structure of synchronous pseudo-SRAM 1000
according to this embodiment. Referring to FIG. 67, synchronous
pseudo-SRAM 1000 includes a DRAM cell array and peripheral circuit
group 1001, a control circuit 1002, a CE buffer 1003, a CLK buffer
1004, a control buffer 1005 and an address buffer 1006.
[0491] The DRAM cell array in DRAM cell array and peripheral
circuit group 1001 is a memory array formed of cells of a Dynamic
Random Access Memory (DRAM). The peripheral circuit group includes
global I/O line pair GIOP (GIO and /GIO) as well as column select
lines provided corresponding to the respective columns, column
select gates, sense amplifiers, preamplifiers, a write driver, a
row decoder, a column decoder and others.
[0492] Address buffer 1006 receives external address signal
ADD[21:0], and produces the internal address signal.
[0493] CE buffer 1003 receives external chip enable signal CE#, and
produces internal chip enable signal INTCE. Internal chip enable
signal INTCE is sent to CLK buffer 1004, control buffer 1005 and
address buffer 1006. These input buffers stop the operations when
internal chip enable signal INTCE is at "L" indicating deactivation
of the chip. When internal chip enable signal INTCE is at "H"
indicating activation of the chip, these input buffers operate
normally. During the stop of operations, these input buffers cannot
hold external signals applied thereto, and cannot provide internal
signals.
[0494] CLK buffer 1004 receives external clock CLK, holds it as a
buffer clock BUFFCLK and produces internal clock INTCLK.
[0495] Control buffer 1005 receives control signals (including
address take-in signal ADV#) other than external chip enable signal
CE#, and produces internal control signals. For example, when
control buffer 1005 receives external address take-in signal ADV#,
it produces internal address take-in signal INTADV.
[0496] Control circuit 1002 includes an ADV0 generating circuit
1010 and a RAS generating circuit 1011.
[0497] ADV0 generating circuit 1010 produces address take-in
trigger signal ADV0 from internal chip enable signal INTCE,
internal clock INTCLK and an inverted internal address take-in
signal ZINTADV.
[0498] RAS generating circuit 1011 produces a row address strobe
signal RAS from address take-in trigger signal ADV0.
[0499] (ADV0 Generating Circuit in the Background Art)
[0500] FIG. 68 shows a structure of an ADV0 generating circuit 1050
in the background art. Referring to FIG. 68, a clocked inverter
CIV1 receives inverted internal address take-in signal ZINTADV. A
NAND circuit NAND1 receives the output of clocked inverter CIV1 and
internal clock INTCLK, and inverter IV1 receives the output of NAND
circuit NAND1. The output of inverter IV1 forms address take-in
trigger signal ADV0.
[0501] (Operation in the Background Art)
[0502] If the ADV0 generating circuit in the background art is
used, the following problem arise when external chip enable signal
CE# is changed asynchronously to external clock CLK.
[0503] FIG. 69 illustrates timing of changes of various signals,
which occur when ADV0 generating circuit 1050 in the background art
is used. Referring to FIG. 69, external clock CLK, external address
take-in signal ADV# and external chip enable signal CE# are applied
as illustrated in FIG. 69. When external chip enable signal CE# is
at "H", CLK buffer 1004 and control buffer 1005 are not operating,
and only CE buffer 1003 takes in external chip enable signal CE#,
and produces internal chip enable signal INTCE. In response to the
activation (i.e., setting to "L") of external chip enable signal
CE#, inverted internal chip enable signal ZINTCE attains "L".
[0504] When inverted internal chip enable signal ZINTCE attains
"L", control buffer 1005 resumes the operation, and takes in
external address take-in signal ADV# to produce internal address
take-in signal INTADV. At this point in time, external address
take-in signal ADV# is at "L" so that inverted internal address
take-in signal ZINTADV is at "L".
[0505] When inverted internal chip enable signal ZINTCE attains
"L", CLK buffer 1004 resumes the operation to take in external
clock CLK, and produces internal clock INTCLK of a constant pulse
width in response to the rising of buffer clock BUFFCLK held
therein. Before inverted internal chip enable signal ZINTCE attains
"L", CLK buffer 1004 does not hold external clock CLK so that
buffer clock BUFFCLK in CLK buffer 1004 indicated at (1) in FIG. 69
does not have a pulse width equal to that of external clock CLK.
This reduces a time interval between first and second internal
clocks INTCLK.
[0506] Clocked inverter CIV1 in ADV0 generating circuit 1050
receives inverted internal address take-in signal ZINTADV, and
provides an output NODEA, which rises to "H" at the rising of
internal clock INTCLK as indicated at (2) in FIG. 69.
[0507] NAND circuit NAND1 and an inverter IV11 in ADV0 generating
circuit 1050 produces address take-in trigger signal ADV0 from
output NODEA of clocked inverter CIV1 and internal clock INTCLK.
The pulses of address take-in trigger signal ADV0 are formed of
leading and subsequent pulses of internal clock INTCLK as indicated
at (3) in FIG. 69.
[0508] RAS generating circuit 1011 activates row address strobe
signal RAS to attain
[0509] "H" in accordance with the rising of the leading pulse of
address take-in trigger signal ADV0. Consequently, row address
strobe signal RAS is activated according to timing, which is
earlier than the intended timing, and precedes the rising (i.e.,
the intended start timing of access) of clock CLK immediately
following the time of input of external chip enable signal CE#, and
this early activation starts the next processing. The above
unpreferable situation and problem have recently been found.
[0510] (ADV0 Generating Circuit of the Embodiment)
[0511] For avoiding the above problem, the ADV0 generating circuit
of this embodiment has a structure different from that in the
background art.
[0512] FIG. 70 shows a structure of ADV0 generating circuit 1010 of
the embodiment. ADV0 generating circuit 1010 includes the same
structure as conventional ADV0 generating circuit 1050, and
additionally includes a delay circuit (Delay) DL11, NOR circuit
NOR95 and an inverter IV12. Referring to FIG. 70, delay circuit
(Delay) DL11 receives inverted internal chip enable signal ZINTCE.
NOR circuit NOR95 receives the output of delay circuit (Delay) DL11
and inverted internal address take-in signal ZINTADV. Inverter IV12
receives the output of NOR circuit NOR95, and provides an inverted
delayed internal address take-in signal ZINTADVD. Clocked inverter
CIV1 receives inverted delayed internal address take-in signal
ZINTADVD. NAND circuit NAND1 receives the output of clocked
inverter CIV1 and internal clock INTCLK, and inverter IV1 receives
the output of NAND circuit NAND1. The output of inverter IV1 forms
address take-in trigger signal ADV0.
Operation of the Embodiment
[0513] FIG. 71 illustrates timing of changes of various signals,
which occur when ADV0 generating circuit 1010 of the embodiment is
used.
[0514] External clock CLK, external address take-in signal ADV#,
external chip enable signal CE#, internal chip enable signal INTCE,
internal address take-in signal INTADV, buffer clock BUFFCLK and
internal clock INTCLK change according to the same timing as that
in the background art already illustrated.
[0515] In ADV0 generating circuit 1010, delay circuit (Delay) DL11,
NOR circuit NOR95 and inverter IV1 receive inverted internal chip
enable signal ZINTCE and inverted internal address take-in signal
ZINTADV, and provide inverted delayed internal address take-in
signal ZINTADVD as indicated at (2) in FIG. 71.
[0516] Clocked inverter CIV1 receives inverted delayed internal
address take-in signal ZINTADVD, and provides an output NODWA,
which rises to "H" at the falling of internal clock INTCLK as
indicated at (3) in FIG. 71.
[0517] In ADV0 generating circuit 1010, NAND circuit NAND1 and
inverter IV11 produce address take-in trigger signal ADV0 from
output NODEA of clocked inverter CIV1 and internal clock INTCLK.
Pulses of address take-in trigger signal ADV0 are formed of second
and subsequent pulses of internal clock INTCLK as indicated at (4)
in FIG. 71. Thus, the leading pulse of address take-in trigger
signal ADV0 produced by ADV0 generating circuit 1010 is formed of
the internal clock pulse produced from the external clock pulse,
which rises during the active state of external address take-in
signal ADV#. Delay circuit (Delay) DL11 has a delay amount, which
is determined to achieve the above.
[0518] RAS generating circuit 1011 activates row address strobe
signal RAS in accordance with the rising of the leading pulse of
address take-in trigger signal ADV0. Consequently, row address
strobe signal RAS is activated according to the same timing as the
intended activation of row address strobe signal RAS, and thus is
activated at the rising of clock CLK immediately following the
input of external chip enable signal CE#. In other words, the delay
amount of delay circuit (Delay) DL11 is set to a value achieving
the above.
[0519] As described above, the synchronous pseudo-SRAM according to
the embodiment stops the operation of the input buffers when the
chip is inactive, and therefore can suppress wasting of the
current.
[0520] Since inverted internal chip enable signal ZINTCE is
delayed, a malfunction does not occur even when external chip
enable signal CE# changes asynchronously.
[0521] The embodiment has been described in connection with the
structure and method for avoiding the problem, which may occur when
external chip enable signal CE# becomes active asynchronously to
the clock in the case where external chip enable signal CE# stops
the input buffers. This is effective regardless of whether external
chip enable signal CE# stops the input buffers or not.
[0522] It is desired that the delay amount of delay circuit DL11 is
equal to or smaller than a quarter of one cycle of external clock
CLK because an excessively large delay amount affects some other
operations.
[0523] The embodiment has been described in connection with the
structure and method for avoiding the problem, which may occur when
external chip enable signal CE# becomes active asynchronously to
the clock. However, even when external chip enable signal CE# is
deactivated asynchronously to the clock, the following problem may
occur. If precharging is performed immediately after data was
written into a memory cell during the inactive state of external
chip enable signal CE#, this may corrupt the data in memory
cells.
[0524] FIG. 72 illustrates such a situation that the timing of
precharging is delayed when external chip enable signal CE# is
deactivated asynchronously to the clock. As illustrated in FIG. 72,
the word line is deactivated when a predetermined time (Delay)
elapses from the falling of column select signal CSL following the
deactivation ("H") of external chip enable signal CE#. Thus, when
the writing is being performed, the word line will be deactivated
after waiting for the correct end of the writing. Thereby, the
corruption of data in the memory cells can be prevented.
[0525] This embodiment is not restrictively applied to the
synchronous pseudo-SRAM, and may be applied to various
semiconductor memory devices operating in synchronization with
clocks.
[0526] As shown in FIG. 70, this embodiment uses clocked inverter
CIV1 as an example of a data holding circuit, which holds the
output of inverter IV12 in synchronization with internal clock
INTCLK. However, this is not restrictive, and another data holding
circuit may be used.
[0527] FIG. 73 shows a structure of an ADV0-generating circuit
including another data holding circuit DH.
[0528] Referring to FIG. 73, data holding circuit DH is formed of a
transmission gate TM transmitting an output of inverter IV12 in
synchronization with internal clock INTCLK, and a flip-flop, which
is formed of inverters IV101 and IV102 for holding an output of
transmission gate TM.
[0529] Although the present invention has been described and
illustrated in detail, it is clearly understood that the same is by
way of illustration and example only and is not to be taken by way
of limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *
References