U.S. patent application number 09/773621 was filed with the patent office on 2001-12-20 for semiconductor memory device having reduced current consumption at internal boosted potential.
This patent application is currently assigned to Mitsubishi Denki Kabushiki Kaisha and Mitsubishi Electric Engineering Company Limited. Invention is credited to Tanizaki, Hiroaki.
Application Number | 20010053098 09/773621 |
Document ID | / |
Family ID | 18671789 |
Filed Date | 2001-12-20 |
United States Patent
Application |
20010053098 |
Kind Code |
A1 |
Tanizaki, Hiroaki |
December 20, 2001 |
Semiconductor memory device having reduced current consumption at
internal boosted potential
Abstract
In a three-state circuit issuing a shared gate signal, after an
N-channel MOS transistor charges a node issuing an output signal
OUT to external power supply potential exvdd, the N-channel MOS
transistor is turned off, and a P-channel MOS transistor is turned
on to charge the node to boosted potential VPP. Thereby, a power
consumed at boosted potential VPP can be reduced, and sizes of
transistors of a VPP generating circuit can be reduced. Thereby, a
semiconductor memory device having a small chip size can be
achieved.
Inventors: |
Tanizaki, Hiroaki; (Hyogo,
JP) |
Correspondence
Address: |
McDERMOTT, WILL & EMERY
600 13th Street, N.W.
Washington
DC
20005-3096
US
|
Assignee: |
Mitsubishi Denki Kabushiki Kaisha
and Mitsubishi Electric Engineering Company Limited
|
Family ID: |
18671789 |
Appl. No.: |
09/773621 |
Filed: |
February 2, 2001 |
Current U.S.
Class: |
365/189.11 |
Current CPC
Class: |
G11C 11/4094 20130101;
G11C 11/4074 20130101; G11C 7/12 20130101 |
Class at
Publication: |
365/189.11 |
International
Class: |
G11C 007/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 6, 2000 |
JP |
2000-168839 (P) |
Claims
What is claimed is:
1. A semiconductor memory device comprising: a memory cell array
including a plurality of memory cells arranged in rows and columns
for storing externally applied data; a voltage generating circuit
for receiving and boosting an externally applied first power supply
potential to generate a second power supply potential to be used
for data transmission with respect to said memory cell array; a
first internal node being activated by said second power supply
potential; a first control circuit for issuing first and second
control signals for driving said first internal node in accordance
with an externally applied input signal, said first control circuit
activating said first control signal for a predetermined time in
accordance with change in said input signal, and activating said
second control signal upon elapsing of said predetermined time
after the change in said input signal; and a first drive circuit
for receiving said first and second power supply potentials, and
driving the potential on said first internal node to said second
power supply potential in accordance with said first and second
control signals, wherein said first drive circuit includes: a first
switch circuit to be turned on to couple said first power supply
potential to said first internal node in accordance with said first
control signal, and a second switch circuit to be turned on to
couple said second power supply potential to said first internal
node in accordance with said second control signal.
2. The semiconductor memory device according to claim 1, wherein
said input signal is a row address signal; said semiconductor
memory device further comprises: a second control signal for
generating third and fourth control signals in accordance with said
row address signals, and a second drive circuit for receiving said
first and second power supply potentials, and driving a potential
on a second internal node to said second power supply potential in
accordance with said third and fourth control signals; and said
memory cell array includes: first bit line pairs provided
corresponding to the columns of said memory cells, respectively, a
sense amplifier for amplifying a potential difference on said first
bit line pair, second and third bit line pairs commonly using said
sense amplifier, a first gate circuit for connecting said first bit
line pair to said second bit line pair in accordance with the
potential on said first internal node, and a second gate circuit
for connecting said first bit line pair to said third bit line pair
in accordance with the potential on said second internal node.
3. The semiconductor memory device according to claim 2, wherein
said first gate circuit includes a first pair of N-channel MOS
transistors having gates connected to said first internal node, and
connected between said first bit line pair and said second bit line
pair, and said second gate circuit has a second pair of N-channel
MOS transistors having gates connected to said second internal
node, and connected between said first bit line pair and said third
bit line pair.
4. The semiconductor memory device according to claim 1, wherein
said memory cell array includes: a bit line pair provided
corresponding to each of the columns of said memory cells, and
having first and second bit lines, and an equalize circuit for
equalizing the potentials on said first and second bit lines with
each other in accordance with the output of said first drive
circuit.
5. The semiconductor memory device according to claim 1, wherein
said first switch circuit has an N-channel MOS transistor to couple
said first power supply potential to said first internal node, and
having a gate receiving said first control signal, and said first
control circuit issues said second power supply potential as an
activation potential of said first control signal.
6. The semiconductor memory device according to claim 1, wherein
said first switch circuit has a P-channel MOS transistor to couple
said first power supply potential to said first internal node, and
having a gate receiving said first control signal.
7. The semiconductor memory device according to claim 6, wherein
said P-channel MOS transistor has a back gate coupled to said
second power supply potential.
8. The semiconductor memory device according to claim 6, wherein
said first control circuit issues said second power supply
potential as a deactivation potential of said first control signal,
and issues the ground potential as an activation potential of said
first control signal.
9. A semiconductor memory device comprising: a memory cell array
including a plurality of memory cells arranged in rows and columns
for storing externally applied data; a voltage generating circuit
for receiving and boosting an externally applied first power supply
potential to generate a second power supply potential to be used
for data transmission with respect to said memory cell array; and a
first drive circuit for receiving said first and second power
supply potentials and a ground potential, and driving a potential
on a first internal node in accordance with an externally applied
input signal, said first drive circuit activating the potential on
said first internal node to attain said second power supply
potential when said input signal indicates access to a first region
in said memory cell array, deactivating the potential on said first
internal node to attain said ground potential when said input
signal indicates access to a second region in said memory cell
array, and coupling the potential on said first internal node to
said first power supply potential when said input signal does not
indicate the access to said memory cell array.
10. The semiconductor memory device according to claim 9, wherein
said input signal is a row address signal, said first drive circuit
is provided corresponding to said first region, said semiconductor
memory device further comprises a second drive circuit provided
corresponding to said second region for driving said second
internal node, and said second drive circuit activates the
potential on said second internal node to attain said second power
supply potential when said input signal indicates the access to the
second region in said memory cell array, deactivates the potential
on said second internal node to attain said ground potential when
said input signal indicates the access to the first region in said
memory cell array, and couples the potential on said second
internal node to said first power supply potential when said input
signal does not indicate the access to said memory cell array.
11. The semiconductor memory device according to claim 10, wherein
said memory cell array includes: a first bit line pair provided
corresponding to each of the columns of said memory cells, a sense
amplifier for amplifying a potential difference on said first bit
line pair, second and third bit line pairs commonly using said
sense amplifier, and provided for said first and second regions,
respectively, a first gate circuit for connecting said first bit
line pair to said second bit line pair in accordance with the
potential on said first internal node, and a second gate circuit
for connecting said first bit line pair to said third bit line pair
in accordance with the potential on said second internal node.
12. The semiconductor memory device according to claim 11, further
comprising: a first control circuit for issuing first, second and
third control signals to control said first drive circuit in
accordance with said address signal, wherein said first control
circuit operates to activate said first control signal and
deactivate said second and third control signals when said address
signal designate said first region, operates to activate said
second control signal and deactivate said first and third control
signals when said address signal designates said second region, and
operates to activate said third control signal and deactivate said
first and second control signals when said address signal does not
indicate the access to said memory cell array; and said first drive
circuit includes: a first switch circuit for coupling said first
internal node to said second power supply potential in accordance
with activation of said first control signal, a second switch
circuit for coupling said first internal node to said ground
potential in accordance with activation of said second control
signal, and a third switch circuit for coupling said first internal
node to said first power supply potential in accordance with
activation of said third control signal.
13. The semiconductor memory device according to claim 12, wherein
said memory array further includes an equalize circuit arranged in
said first region for equalizing the potentials on said second bit
line pair when the access to said first region is not performed,
and said first control circuit deactivates said first control
signal after a predetermined time from end of the access to said
first region subsequent to designation of said first region by said
address signal.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a semiconductor memory
device, and particularly a semiconductor memory device having a
memory cell array of a shared sense amplifier type.
[0003] 2. Description of the Background Art
[0004] In a Dynamic Random Access Memory (DRAM), a boosted
potential VPP is used for driving signal lines bearing large loads
when reading data from a memory array, and more specifically for
driving a word line, a bit line equalize signal line (BLEQ) and a
shared gate signal line (BLI) of a memory cell array of a shared
sense amplifier type, which will be described later. Gate circuits
which are connected to these signal lines employ N-channel MOS
transistors. For transmitting a power supply potential, which is
applied to a source of the N-channel MOS transistor, to a drain, it
is necessary to apply a H-level, which is higher than the power
supply potential by at least an amount corresponding to a threshold
voltage, as a gate potential. Therefore, boosted potential VPP is
required.
[0005] FIG. 17 shows boosted potential VPP which is internally
generated.
[0006] Referring to FIG. 17, boosted potential VPP is generated by
a VPP generating circuit arranged within a semiconductor memory
device. In VPP generating circuit, an external power supply
potential exvdd which is externally supplied to the semiconductor
memory device is boosted by a booster circuit such as a charge pump
circuit or the like, and thereby boosted potential VPP is
generated.
[0007] In recent years, however, external power supply potential
exvdd has been lowered to increase a potential difference from
required boosted potential VPP. Since VPP generating circuit boosts
external power supply potential exvdd, which is low, by a charge
pump or the like, increase in power consumption at boosted
potential VPP requires the charge pump to be formed of transistors
having increased sizes. Thereby, the chip area of the semiconductor
memory device increases.
[0008] In the prior art, therefore, it has been necessary to devise
a structure and/or a method for suppressing the power consumption
at boosted potential VPP.
[0009] FIG. 18 is a circuit diagram showing a structure of a
three-state circuit which is used in the prior art for suppressing
power consumption at boosted potential VPP.
[0010] Referring to FIG. 18, this three-state circuit includes a
P-channel MOS transistor PQ which is connected between a node
receiving boosted potential VPP and an output node NOUT, and
receives on its gate a signal A, an N-channel MOS transistor NQ
which is connected between output node NOUT and a ground node, and
receives on its gate a signal B, and an N-channel MOS transistor NQ
1 which is connected between a node receiving external power supply
potential exvdd and output node NOUT, and receives on its gate a
control signal C.
[0011] For changing the output from 0 V to boosted potential VPP,
this three-state circuit operates in such a manner that output node
NOUT is boosted from 0 V to external power supply potential exvdd
in a first stage, and then the potential on output node NOUT is
boosted external power supply potential exvdd to boosted potential
VPP in the second stage. In this manner, the power which is
consumed at boosted potential VPP generated by VPP generating
circuit can be merely equal to that required for boosting the
potential from external power supply potential exvdd to boosted
potential VPP.
[0012] FIG. 19 is an operation waveform diagram showing an
operation of the three-state circuit shown in FIG. 18.
[0013] Referring to FIGS. 18 and 19, the potential of signal A
changes from 0 V to boosted potential VPP at time t1, the potential
of signal B changes from 0 V to boosted potential VPP and the
potential of control signal C changes from external power supply
potential exvdd to the ground potential. Thereby, P- and N-channel
MOS transistors PQ and NQ 1 are turned off, and N-channel MOS
transistor NQ is turned on so that output node NOUT is coupled to
the ground node. Therefore, output signal OUT lowers to
L-level.
[0014] At a time t2, the potential of signal B falls from boosted
potential VPP to the ground potential, and the potential of control
signal C rises from the ground potential to external power supply
potential exvdd. Thereby, N-channel MOS transistor NQ is turned
off, and N-channel MOS transistor NQ1 is turned on so that output
node NOUT is coupled to external power supply potential exvdd by
N-channel MOS transistor NQ1. However, the gate potential of
N-channel MOS transistor NQ1 is equal to external power supply
potential exvdd. Therefore, voltage drop by an amount equal to
threshold voltage Vth occurs. For a period between t2 and t3,
therefore, output node NOUT is charged to attain a potential which
is lower than external power supply potential exvdd by an amount
equal to the threshold voltage.
[0015] At a time t3, the potential of signal A lowers from boosted
potential VPP to L-level. Thereby, P-channel MOS transistor PQ is
turned on, and output node NOUT is coupled to boosted potential
VPP. Therefore, the potential of signal OUT rises from a value of
(exvdd-Vth) to boosted potential VPP after time t3. Thereby, the
power consumption at boosted potential VPP generated by the VPP
generating circuit is merely caused by the boosting after time
t3.
[0016] However, the potential difference between boosted potential
VPP and external power supply potential exvdd has been considerably
increased in accordance with lowering of the external power supply
potential. Therefore, the potential on the output node is raised by
a large amount after time t3 so that the effect of reducing the
power consumption at boosted potential VPP has been reduced.
[0017] For increasing the effect of reducing the power consumption
while preventing the potential from lowering by the magnitude
corresponding to threshold voltage Vth, the potential of control
signal C at H-level can be equal to boosted potential VPP. In this
case, however, P- and N-channel MOS transistors PQ and NQ1 couple
boosted potential VPP to external power supply potential exvdd when
output node NOUT is coupled to boosted potential VPP by P-channel
MOS transistor PQ. Thereby, leak from boosted potential VPP to
external power supply potential exvdd occurs.
SUMMARY OF THE INVENTION
[0018] An object of the invention is to provide a semiconductor
memory device, in which power consumption at boosted potential VPP
is reduced so that sizes of transistors contained in a VPP
generating circuit and therefore a chip area can be small.
[0019] In summary, the invention provides a semiconductor memory
device including a memory cell array, a voltage generating circuit,
a first internal node, a first control circuit and a first drive
circuit.
[0020] The memory cell array includes a plurality of memory cells
arranged in rows and columns for storing externally applied data.
The voltage generating circuit receives and boosts an externally
applied first power supply potential to generate a second power
supply potential to be used for data transmission with respect to
the memory cell array. The first internal node is activated by the
second power supply potential. The first control circuit issues
first and second control signals for driving the first internal
node in accordance with an externally applied input signal. The
first control circuit activates the first control signal for a
predetermined time in accordance with change in the input signal,
and activates the second control signal upon elapsing of the
predetermined time after the change in the input signal. The first
drive circuit receives the first and second power supply
potentials, and drives the potential on the first internal node to
the second power supply potential in accordance with the first and
second control signals. The first drive circuit includes a first
switch circuit to be turned on to couple the first power supply
potential to the first internal node in accordance with the first
control signal, and a second switch circuit to be turned on to
couple the second power supply potential to the first internal node
in accordance with the second control signal.
[0021] According to another aspect, the invention provides a
semiconductor memory device including a memory cell array, a
voltage generating circuit and a first drive circuit.
[0022] The memory cell array includes a plurality of memory cells
arranged in rows and columns for storing externally applied data.
The voltage generating circuit receives and boosts an externally
applied first power supply potential to generate a second power
supply potential to be used for data transmission with respect to
the memory cell array. The first drive circuit receives the first
and second power supply potentials and a ground potential, and
drives a potential on a first internal node in accordance with an
externally applied input signal. The first drive circuit activates
the potential on the first internal node to attain the second power
supply potential when the input signal indicates access to a first
region in the memory cell array, deactivates the potential on the
first internal node to attain the ground potential when the input
signal indicates access to a second region in the memory cell
array, and couples the potential on the first internal node to the
first power supply potential when the input signal does not
indicate the access to the memory cell array.
[0023] Accordingly, the invention can achieve such an advantage
that the power consumption at a boosted potential can be
suppressed, and thereby sizes of a voltage generating circuit for
generating the boosted potential and therefore a chip size can be
reduced.
[0024] 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
[0025] FIG. 1 is a schematic block diagram showing a whole
structure of a semiconductor memory device 1 according to the
invention;
[0026] FIG. 2 is a block diagram showing a structure of a control
signal generating portion included in a row decoder 26 shown in
FIG. 1;
[0027] FIG. 3 is a circuit diagram showing a structure of a control
circuit 42 shown in FIG. 2;
[0028] FIG. 4 is a circuit diagram showing a structure of a level
converting circuit 66 shown in FIG. 3;
[0029] FIG. 5 is a circuit diagram showing a structure of a
three-state circuit 44 shown in FIG. 2;
[0030] FIG. 6 is a circuit diagram showing a structure of a portion
of a memory cell array of a shared sense amplifier type, and more
specifically a connection portion between a memory cell array 32
and a sense amplifier 30 shown in FIG. 1;
[0031] FIG. 7 is an operation waveform diagram showing an operation
of three-state circuit 44;
[0032] FIG. 8 shows a problem of a transistor of the three-state
circuit in the first embodiment;
[0033] FIG. 9 is a circuit diagram showing a structure of a
three-state circuit 44a used in a second embodiment;
[0034] FIG. 10 is an operation waveform diagram showing an
operation of three-state circuit 44a shown in FIG. 9;
[0035] FIG. 11 is a block diagram showing a structure of a control
signal generating portion included in a row decoder used in a third
embodiment;
[0036] FIG. 12 is a circuit diagram showing a structure of a
control circuit 122 shown in FIG. 11;
[0037] FIG. 13 is an operation waveform diagram showing an
operation of a third embodiment;
[0038] FIG. 14 is a circuit diagram showing a structure of a
control circuit 122a in a fourth embodiment;
[0039] FIG. 15 is an operation waveform diagram showing an
operation of a three-state circuit in the case of use of control
circuit 122a;
[0040] FIG. 16 is an operation waveform diagram showing a data read
operation in the fourth embodiment;
[0041] FIG. 17 shows a boosted potential VPP which is internally
generated;
[0042] FIG. 18 is a circuit diagram showing a structure of a
three-state circuit, which is used in the prior art for suppressing
a power consumption at boosted potential VPP; and
[0043] FIG. 19 is an operation waveform diagram for showing an
operation of a three-state circuit in FIG. 18.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0044] Embodiments of the invention will now be described in
greater detail with reference to the drawings. In the figures, the
same or corresponding portions bear the same reference numbers.
[0045] [First Embodiment]
[0046] FIG. 1 is a schematic block diagram showing a whole
structure of a semiconductor memory device 1 according to the
invention.
[0047] Referring to FIG. 1, semiconductor memory device 1 includes
control signal input terminals 2, 4 and 6 which receive control
signals Ext./RAS, Ext./CAS and Ext./WE, respectively, an address
input terminal group 8, a terminal group 14 for input/output of
data signals DQ0-DQn, a ground terminal 12 supplied with a ground
potential Vss, and a power supply terminal 10 supplied with
external power supply potential exvdd.
[0048] Semiconductor memory device 1 further includes a clock
generating circuit 22, a row and column address buffer 24, a row
decoder 26, a column decoder 28, a sense amplifier pulse
I/O-control circuit 30, a memory cell array 32, a gate circuit 18,
a data input buffer 20 and a data output buffer 34.
[0049] Clock generating circuit 22 controls a whole operation of
the semiconductor memory device by issuing a control clock which
corresponds to a predetermined operation mode based external row
address strobe signal Ext./RAS and external column address strobe
signal Ext./CAS, which are externally supplied via control signal
input terminals 2 and 4, respectively.
[0050] Row and column address buffer 24 applies the address
signals, which are produced based on externally applied address
signals A0-Ai (i: natural number), to row and column decoders 26
and 28.
[0051] Data signals DQ0-DQn can be externally sent from or to the
memory cell in memory cell array 32, which is designated by row and
column decoders 26 and 28, through I/O terminal 14 as well as sense
amplifier plus I/O control circuit 30 and data I/O buffer 20 (or
data output buffer 34).
[0052] Semiconductor memory device 1 further includes a VPP
generating circuit 36, which generates boosted potential VPP by
receiving and boosting external power supply potential exvdd
applied to power supply potential 10. Boosted potential VPP is
supplied to memory cell array 32 and sense amplifier plus I/O
control circuit 30 as a drive potential of a gate circuit, which is
provided for isolating the bit line of the memory array of the
shared sense amplifier structure type described later from the
sense amplifier.
[0053] Semiconductor memory device 1 shown in FIG. 1 is a typical
example, and the invention can also be applied, e.g., to a
synchronous semiconductor memory device (SDRAM).
[0054] FIG. 2 is a block diagram showing a structure of a control
signal generating portion included in row decoder 26 shown in FIG.
1.
[0055] Referring to FIG. 2, the control signal generating portion
includes a control circuit 42 which receives a block select signal
BLKR, and issues control signals AL, BL and CL, a three-state
circuit 44 which receives control signals AL, BL and CL, and issues
a shared gate signal BLIL, a control circuit 46 which receives a
block select signal BLKL, and issues control signals AR, BR and CR,
and a three-state circuit 48 which receives control signals AR, BR
and CR, and issues shared gate signal BLIR.
[0056] FIG. 3 is a circuit diagram showing a structure of control
circuit 42 shown in FIG. 2.
[0057] Referring to FIG. 3, control circuit 42 includes a delay
circuit 52 which receives and delays block select signal BLK by a
predetermined time, an NOR circuit 54 which receives block select
signal BLK and the output of delay circuit 52, a level converting
circuit 56 which receives the output of NOR circuit 54, and
converts the level thereof to issue control signal A, inverters 58
and 62 which receive and invert block select signal BLK, a level
converting circuit 60 which receives the output of inverter 58, and
converts the level thereof to issue control signal B, an AND
circuit 64 which receives the outputs of delay circuit 52 and
inverter 62, and a level converting circuit 66, which receives the
output of AND circuit 64 and converts the level thereof to issue
control signal C.
[0058] Block select signal BLKR and control signals AL, BL and CL
shown in FIG. 2 correspond to block select signal BLK and control
signals A, B and C in FIG. 3, respectively.
[0059] Control circuit 46 shown in FIG. 2 has the substantially
same structure as control circuit 42, and thereof description
thereof is not repeated. In this case, block select signal BLKL and
control signals AR, BR and CR shown in FIG. 2 correspond to block
select signal BLK and control signals A, B and C in FIG. 3,
respectively.
[0060] FIG. 4 is a circuit diagram showing a structure of level
converting circuit 66 shown in FIG. 3.
[0061] Referring to FIG. 4, level converting circuit 66 includes an
inverter 72 which receives and inverts an input signal IN, an
N-channel MOS transistor 76 which is connected between a node N51
and the ground node, and has a gate receiving input signal IN, a
P-channel MOS transistor 74 which is connected between a node
supplied with boosted potential VPP and node N51, and has a gate
connected to a node N52, an N-channel MOS transistor 80 which is
connected between node N52 and the ground node, and has a gate
receiving the output of inverter 72, and a P-channel MOS transistor
78 which is connected between a node supplied with boosted
potential VPP and node N52, and has a gate connected to node N51.
Output signal OUT of level converting circuit 66 is issued from
node N52.
[0062] Level converting circuits 56 and 60 shown in FIG. 3 have the
substantially same structures as level converting circuit 66 shown
in FIG. 4, and therefore description thereof is not repeated.
[0063] FIG. 5 is a circuit diagram showing a structure of
three-state circuit 44 shown in FIG. 2.
[0064] Referring to FIG. 5, three-state circuit 44 includes a
P-channel MOS transistor 92 which is connected between a node
supplied with boosted potential VPP and a node N53, and has a gate
receiving control signal A, an N-channel MOS transistor 94 which is
connected between node N53 and the ground node, and has a gate
receiving control signal B, and an N-channel MOS transistor 96
which is connected between a node supplied with external power
supply potential exvdd and node N53, and has a gate receiving
control signal C. Output signal OUT of three-state circuit 44 is
issued from node N53.
[0065] Control signals AL, BL and CL, and shared gate signal BLIL
in FIG. 2 correspond to control signals A, B and C, and output
signal OUT in FIG. 5, respectively.
[0066] Three-state circuit 48 in FIG. 2 has the substantially same
structure as three-state circuit 44, and therefore description
thereof is not repeated. In this case, control signals AR, BR and
CR, and shared gate signal BLIL in FIG. 2 correspond to control
signals A, B and C, and output signal OUT in FIG. 5.
[0067] FIG. 6 is circuit diagram showing a structure of a portion
of the memory cell array of the shared sense amplifier type, and
more specifically a connecting portion between memory cell array 32
and sense amplifier 30 in FIG. 1.
[0068] Referring to FIG. 6, the memory cell array of the shared
sense amplifier type will now be described briefly. The memory
cells are divided into two blocks L and R, which commonly use a
sense amplifier band. The sense amplifier band is disposed in the
connection portion between blocks L and R. As described above, the
addresses which are not simultaneously accessed are divided into
blocks, and the plurality of blocks commonly use the sense
amplifiers. This structure is referred to as the shared sense
amplifier type of the memory cell array.
[0069] This connection portion includes a sense amplifier 102 which
expands the potential difference between bit lines BL0 and /BL0 for
outputting it, a gate circuit 104 which connects bit lines BL0 and
/BL0 to bit lines BLL and /BLL, respectively, in accordance with a
shared gate signal BLIL, a gate circuit 106 which connects bit
lines BL0 and /BL0 to bit lines BLR and /BLR, respectively, in
accordance with a shared gate signal BLIR, an equalize circuit 108
which equalizes the potentials on bit lines BLL and /BLL in
accordance with an equalize signal BLEQL, and an equalize circuit
110 which equalizes the potentials on bit lines BLR and /BLR in
accordance with an equalize signal BLEQR. Memory cell MC is
arranged at each crossing between the bit line and the word
line.
[0070] Although a plurality of word lines are actually arranged in
each of blocks L and R, FIG. 6 shows only one word line and one
memory cell as a typical example. Memory cell MC includes an access
transistor 112 which has a gate connected to the word line, and is
connected between bit line BLL and a storage node, and a capacitor
114 which is arranged between the storage node and the ground
node.
[0071] Although not shown, equalize circuit 108 includes first,
second and third N-channel MOS transistors, which are usually
turned on in response to equalize signal BLEQL. When turned on, the
first N-channel MOS transistor connects bit lines BLL and /BLL
together, the second N-channel MOS transistor couples bit line BLL
to cell plate potential VCP, and couples bit line /BL to cell plate
potential VCP. Equalize circuit 110 has the substantially same
structure as equalize circuit 108.
[0072] FIG. 7 is an operation waveform diagram showing an operation
of three-state circuit 44.
[0073] Referring to FIG. 7, block select signal BLKL rises from
L-level to H-level at time t1 for reading data from block L shown
in FIG. 6 in accordance with the externally applied row address.
Thereby, for isolating sense amplifier 102 in FIG. 6 from block R,
gate circuit 106 is turned off. For issuing this shared gate signal
BLIR, control circuit 46 in FIG. 2 operates in response to block
select signal BLKL to boost signal AR from L-level to boosted
potential VPP and boost signal BR from the ground potential to
external power supply potential exvdd or boosted potential VPP. In
accordance with this, P-channel MOS transistor 92 shown in FIG. 5
is turned off, and N-channel MOS transistor 94 is turned on.
Accordingly, shared gate signal BLIR issued from three-state
circuit 48 falls from boosted potential VPP to the ground
potential. Thereby, gate circuit 106 is turned off, and block R is
isolated from sense amplifier 102 for a period between times t1 and
t2.
[0074] At subsequent time t2, block select signal BLKL falls from
H-level to L-level for returning to the standby state in accordance
with completion of the operation of reading data from block L. In
accordance with this, control circuit 46 in FIG. 2 lowers signal BR
from H-level to L-level. Control signal CR is set to H-level taking
the form of pulse for a period equal to a delay time of delay
circuit 52 shown in FIG. 3. Level converting circuit 66 converts
this H-level to boosted potential VPP level as shown in FIG. 4 so
that the H-level of control signal CR for the period between times
t2 and t3 is equal to boosted potential VPP.
[0075] In the first embodiment, therefore, the output node is
charged to attain external power supply potential exvdd as can be
seen from a waveform W2 in contrast to the prior art, in which the
charging is performed to attain the potential lower than external
power supply potential exvdd by threshold voltage Vth as shown in a
waveform W1.
[0076] At time t3, control signal AR falls from H-level to L-level
in accordance with the fact that a time equal to the delay time of
delay circuit 52 in FIG. 3 elapsed after the falling of block
select signal BLKL. Also, control signal CR falls from H-level to
L-level. Thereby, N-channel MOS transistor 96 in FIG. 5 is turned
off, and alternatively, P-channel MOS transistor 92 is turned on.
When P-channel MOS transistor 92 is turned on in this manner,
N-channel MOS transistor 96 is turned off so that a leak current
does not flow from boosted potential VPP to external power supply
potential exvdd.
[0077] Accordingly, the potential on the output node of three-state
circuit 48, which issues the shared gate signal, can be charged to
external power supply potential exvdd by applying, as control
signal CR, the pulse signal of which H-level is defined by the
boosted potential. The leak current does not occur, and the power
consumption at boosted potential VPP can be merely equal to the
consumption required for changing the potential from external power
supply potential exvdd to boosted potential VPP. Therefore,
elements included in the circuit for generating boosted potential
VPP can have small sizes.
[0078] In the DRAM, word lines WL in the memory array shown in FIG.
6 as well as equalize signal lines receiving equalize signals BLEQL
and BLEQR are usually driven by boosted potential VPP.
[0079] The word line is selected in accordance with the row address
signal, and the selected word line is activated to attain boosted
potential VPP. Bit line equalize signals BLEQL and BLEQR are kept
active, and therefore at the level of boosted potential VPP for a
period immediately before row selection according to the row
address signal, and are deactivated when the word line is
activated. When reading or writing of data is completed, the word
line is deactivated, and bit line equalize signals BLEQL and BLEQR
are activated again so that bit line pair is equalized for the next
read or write operation. The three-state circuit shown in FIG. 5
may be used as a drive circuit for the word line and the equalize
signal line.
[0080] In this case, the power consumption at boosted potential VPP
can be reduced so that the elements of reduced sizes can be
employed in the circuit for generating boosted potential VPP.
[0081] [Second Embodiment]
[0082] FIG. 8 shows a problem of the transistor in the three-state
circuit of the first embodiment.
[0083] Referring to FIG. 8, three-state circuit 44 uses an
N-channel MOS transistor 96 for charging output node N53. In
N-channel MOS transistor 96, a large potential difference (Vb-s) is
present between the substrate potential and the source
potential.
[0084] In recent years, the concentration of implanted impurities
in the transistor has been increased in accordance with reduction
in sizes. In general, as the potential difference between the
substrate and the source increases, the substrate bias effect
increases the threshold voltage of the transistor. The threshold
voltage increases in proportion to the substrate bias effect, and
the constant of this proportionality tends to increase as the
concentration of implanted impurities increases. The structure in
which the N-channel MOS transistor is employed as the transistor
for charging node N53 as shown in FIG. 8 may cause such a problem
that the charged voltage on node N53 is lowered by an amount equal
to the increased amount of the threshold voltage if the active
potential of control signal C is not sufficiently high.
[0085] FIG. 9 is a circuit diagram showing a structure of a
three-state circuit 44a used in the second embodiment.
[0086] Referring to FIG. 9, three-state circuit 44a differs from
three-state circuit 44 in the first embodiment in that a P-channel
MOS transistor 96a is employed instead of N-channel MOS transistor
96. P-channel MOS transistor 96a has a gate receiving control
signal C, and is connected between node N53 and a node supplied
with external power supply potential exvdd. Other structures are
the same as those of three-state circuit 44, and therefore
description thereof is not repeated.
[0087] Control signal C in the second embodiment is formed of an
inverted signal of control signal C in the first embodiment. In
this case, a back gate of P-channel MOS transistor 96a is coupled
to boosted potential VPP. Since external power supply potential
exvdd is smaller than boosted potential VPP, leak of a current from
the source of P-channel MOS transistor 96a to the back gate does
not occur. Even when P-channel MOS transistor 92 couples node N53
to boosted potential VPP, the leak current does not flow from node
N53 to the back gate of P-channel MOS transistor 96a because both
the potentials on node N53 and the back gate of P-channel MOS
transistor 96a are equal to VPP, and no potential difference is
present between them.
[0088] FIG. 10 is an operation waveform diagram showing an
operation of three-state circuit 44a shown in FIG. 9.
[0089] Control signals AR and BR have the same waveforms as those
already described in FIG. 7, and description thereof is not
repeated.
[0090] Control signal CR has an inverted waveform of control signal
CR shown in FIG. 7. The inverted waveform can be produced by adding
an inverter to the output of level converting circuit 66 shown in
FIG. 3. Node N51 shown in FIG. 4 may be used as an inverted
output.
[0091] Control signal CR falls from H-level to L-level at time t2,
and rises from L-level to H-level at time t3. Thereby, the
potential which is placed on node N53 by charging for a period
between times t2 and t3 does not lower by an amount equal to the
threshold voltage, and the charging can be performed until the
potential reaches external power supply potential exvdd. Therefore,
the second embodiment can likewise reduce the power consumed at
boosted potential VPP.
[0092] [Third Embodiment]
[0093] FIG. 11 is a block diagram showing a structure of a control
signal generating portion included in a row decoder used in a third
embodiment.
[0094] Referring to FIG. 11, the control signal generating portion
of the third embodiment includes a control circuit 122 which
receives block select signals BLKL and BLKR produced in accordance
with the row address signal, and issues control signals, AL, BL and
CL, a three-state circuit 124 which receives control signals AL, BL
and CL, and issues shared gate signal BLIL, a control circuit 126
which receives block select signals BLKL and BLKR, and issues
control signals AR, BR and CR, and a three-state circuit 128 which
receives control signals AR, BR and CR, and issues shared gate
signal BLIR.
[0095] FIG. 12 is a circuit diagram showing a structure of control
circuit 122 shown in FIG. 11.
[0096] Referring to FIG. 12, control circuit 122 includes an
inverter 132 which receives and inverts a block select signal BLK1,
a level converting circuit 134 which receives the output of
inverter 132, and converts the level thereof to issue control
signal A, a level converting circuit 136 which receives a block
select signal BLK2, and converts the level thereof to issue control
signal B, an inverter 138 which receives and inverts block select
signal BLK2, an NAND circuit 140 which receives the outputs of NAND
circuit 132 and inverter 138, and a level converting circuit 142
which receives the output of NAND circuit 140, and converts the
level thereof to issue control signal C.
[0097] Control circuit 122 receives block select signal BLKL as
block select signal BLK1, and also receives block select signal
BLKR as block select signal BLK2. Control signals A, B and C are
issued as control signals AL, BL and CL in FIG. 11,
respectively.
[0098] Since the control circuit 126 in FIG. 11 has the
substantially same structure as control circuit 122, description
thereof is not repeated. Control circuit 126 receives block select
signal BLKR as block select signal BLK1, and also receives block
select signal BLKL as block select signal BLK2. Control signals A,
B and C are issued as control signals AR, BR and CR in FIG. 11,
respectively.
[0099] Level converting circuits 134, 136 and 142 have the
substantially same structures as level converting circuit 136 shown
in FIG. 4, and therefore description thereof is not repeated.
[0100] FIG. 13 is an operation waveform diagram showing an
operation of the third embodiment.
[0101] According to the structures shown in FIGS. 11 and 12, the
potential of the shared gate signal is set to external power supply
potential exvdd while the block is not selected, and in other
words, for the standby periods before time t1 in FIG. 13, between
times t2 and t3, and after time t4. Thereby, the current
consumption at boosted potential VPP during standby can be reduced.
The block select signal is issued based on the row address applied
to the row decoder. At time t1, block select signal BLKL is
activated so that shared gate signal BLIL attains boosted potential
VPP, and shared gate signal BLIR attains the ground potential. In
time t3, when block select signal BLKR is activated, shared gate
signal BLIR attains boosted potential VPP, and shared gate signal
BLIL attains the ground potential. Thereby, the signal on the bit
line on the selected memory cell side is read out by the sense
amplifier.
[0102] In the third embodiment, as described above, the potential
of the shared gate signal during standby is equal to the external
power supply potential. Therefore, the power consumed at boosted
potential VPP generated by the VPP generating circuit can be
reduced during standby.
[0103] [Fourth Embodiment]
[0104] According to a fourth embodiment, a control circuit 122a is
used instead of control circuit 122 in FIG. 11.
[0105] FIG. 14 is a circuit diagram showing a structure of control
circuit 122a of the fourth embodiment.
[0106] Referring to FIG. 14, control circuit 122a includes a delay
circuit 152 which receives and delays block select signal BLKl by a
predetermined time, an NOR circuit 154 which receives block select
signal BLK1 and the output of delay circuit 152, a level converting
circuit 156 which receives the output of NOR circuit 154, and
converts the level thereof to issue control signal A, a level
converting circuit 158 which receives block select signal BLK2, and
converts the level thereof to issue control signal B, an inverter
160 which receives and inverts block select signal BLK2, an NAND
circuit 162 which receives the outputs of NOR circuit 154 and
inverter 160, and a level converting circuit 164 which receives the
output of NAND circuit 162, and issues control signal C. In the
fourth embodiment, control circuit 126 shown in FIG. 11 has the
substantially same structure as that already described with
reference to FIG. 14, and description thereof is not repeated.
[0107] FIG. 15 is an operation waveform diagram showing an
operation of the three-state circuit provided with control circuit
122a.
[0108] Referring to FIG. 15, block select signal BLKL rises from
L-level to H-level at time t1. Thereby, control signal CL rises
from L-level to H-level, and P-channel MOS transistor 96a in FIG.
96a is turned off. Also, control signal AL falls from H-level to
L-level, and P-channel MOS transistor 92 is turned on. Therefore,
shared gate signal BLIL issued from the three-state circuit rises
from external power supply potential exvdd to boosted potential
VPP. Control signal BR rises from L-level to H-level, and shared
gate signal BLIR attains the ground potential so that the gate
circuit isolates block R from the sense amplifier.
[0109] At time t2, block select signal BLKL falls from H-level to
L-level, and thereby control signal BR falls from H-level to
L-level so that shared gate signal BLIR rises from the ground
potential to external power supply potential exvdd. In this case,
shared gate signal BLIL is kept at boosted potential VPP. When a
delay time Td elapses from time t2, control signal AL rises from
L-level to H-level, and control signal CL falls from H-level to
L-level. Thereby, shared gate signal BLIL lowers from boosted
potential VPP to external power supply potential exvdd.
[0110] At time t3, block select signal BLKR rises from L-level to
H-level, and thereby control signal BL rises from L-level to
H-level so that shared gate signal BLIL falls from external power
supply potential exvdd to the ground potential. Control signal AR
falls from H-level to L-level, and control signal CR rises from
L-level to H-level so that shared gate signal BLIR rises from
external power supply potential exvdd to boosted potential VPP.
[0111] At time t4, block select signal BLKR falls from H-level to
L-level. Thereby, control signal BL falls from H-level to L-level,
and shared gate signal BLIL rises from the ground potential to
external power supply potential exvdd. When delay time Td elapses
from time t4, control signal AR rises from L-level to H-level, and
control signal CR falls from H-level to L-level so that shared gate
signal BLIR lowers from boosted potential VPP to external power
supply potential exvdd.
[0112] FIG. 16 is an operation waveform diagram showing a data read
operation in the fourth embodiment.
[0113] Referring to FIGS. 6 and 16, block select signal BLKL rises
from L-level to H-level at time t1. For reading out the data from
the memory cell in block L, therefore, equalize signal BLEQL falls
to L-level, and bit lines BLL and /BLL are released from the
equalized state. Shared gate signal BLIL attains boosted potential
VPP, and bit lines BL and /BL are coupled to bit lines BLL and
/BLL, respectively. Since shared gate signal BLIR falls to the
ground potential, bit lines BL and /BL are isolated from bit lines
BLR and /BLR, respectively. Thereafter, word line WL is activated,
and the potential on the bit line changes from equalized potential
VBL in accordance with the data stored in memory cell MC. Sense
amplifier 102 amplifies the potential difference occurred on the
bit line pair so that data reading is performed.
[0114] When the read operation is completed at time t2, block
select signal BLKL falls to L-level. Thereby, equalize signal BLEQL
rises to H-level, and bit lines BLL and /BLL are set to equalized
potential VBL again. At this point of time, since shared gate
signal BLIL is held at boosted potential VPP, bit lines BL and /BL
are charged to potential VBL by equalize circuit 108. Therefore,
gate circuit 104 is held in the state providing a small
on-resistance for a period of equalizing bit lines BL and /BL.
Accordingly, the equalize time of bit lines BL and /BL can be
reduced from a conventional value of .DELTA.tEQ1 to
.DELTA.tEQ2.
[0115] According to the semiconductor memory device of the fourth
embodiment, as already described, the time required for equalizing
bit lines BL and /BL connected to the sense amplifier is reduced by
such a manner that the shared gate signal is held at the raised
potential, and thereby the gate circuit is held in the state
providing a small on-resistance for a period equal to the
predetermined delay time before the potential is externally
restored to external power supply potential exvdd during the
standby. Accordingly, the equalize circuit arranged on the memory
cell side can rapidly charge the bit lines.
[0116] 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.
* * * * *