U.S. patent application number 11/445944 was filed with the patent office on 2007-07-19 for apparatus and method for reducing test resources in testing drams.
Invention is credited to Scott L. Ayres, David R. Brown, Chris Cooper, Scott N. Gatzemeier, Siang Tian Giam, Jerry D. McBride.
Application Number | 20070168790 11/445944 |
Document ID | / |
Family ID | 23806198 |
Filed Date | 2007-07-19 |
United States Patent
Application |
20070168790 |
Kind Code |
A1 |
Cooper; Chris ; et
al. |
July 19, 2007 |
Apparatus and method for reducing test resources in testing
drams
Abstract
An apparatus and a method are disclosed for reducing the pin
driver count required for testing computer memory devices,
specifically Rambus DRAM, while a die is on a semiconductor wafer.
By reducing the pin count, more DRAMs can be tested at the same
time, thereby reducing test cost and time. One preferred embodiment
utilizes a trailing edge of a precharge clock to select a new
active bank address, so that the address line required to select a
new active address does not have to be accessed at the same time as
the row lines.
Inventors: |
Cooper; Chris; (Boise,
ID) ; Giam; Siang Tian; (Singapore, SG) ;
McBride; Jerry D.; (Boise, ID) ; Gatzemeier; Scott
N.; (Boise, ID) ; Ayres; Scott L.; (Meridian,
ID) ; Brown; David R.; (Allen, TX) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
23806198 |
Appl. No.: |
11/445944 |
Filed: |
June 2, 2006 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10853573 |
May 25, 2004 |
7168018 |
|
|
11445944 |
Jun 2, 2006 |
|
|
|
09653112 |
Aug 31, 2000 |
6854079 |
|
|
10853573 |
May 25, 2004 |
|
|
|
09454808 |
Dec 3, 1999 |
6530045 |
|
|
09653112 |
Aug 31, 2000 |
|
|
|
Current U.S.
Class: |
714/724 |
Current CPC
Class: |
G11C 29/26 20130101;
G01R 31/31932 20130101; G11C 29/14 20130101; G11C 29/48 20130101;
G11C 29/40 20130101; G11C 2029/5602 20130101; G11C 11/401 20130101;
G11C 29/006 20130101; G11C 29/1201 20130101; G11C 29/12015
20130101; G11C 29/56 20130101 |
Class at
Publication: |
714/724 |
International
Class: |
G01R 31/28 20060101
G01R031/28 |
Claims
1. (canceled)
2. A wafer probe for testing a memory device, the wafer probe
comprising: a plurality of conductive pins having a control pin
configured to output to at least one memory device a control signal
having a precharge signal defined by a first portion of the control
signal and a latch signal defined by a second portion of the
control signal.
3. The wafer probe of claim 2, wherein the first portion of the
control signal is a leading edge of the control signal.
4. The wafer probe of claim 3, wherein the second portion of the
control signal is a trailing edge of the control signal.
5. The wafer probe of claim 2, wherein the at least one memory
device comprises a dynamic random access memory (DRAM).
6. The wafer probe of claim 2, wherein the plurality of conductive
pins is configured to positionally align with bonding pads of at
least three memory devices to be tested.
7. The wafer probe of claim 2, further comprising compare circuitry
configured to compare data read from the at least one memory device
with test data in order to test the integrity of the at least one
memory device.
8. Control circuitry for use with a wafer probe in testing a
computer memory device, the control circuitry comprising: a first
input configured to receive from a control pin of a wafer probe a
control signal having a precharge signal defined by a first portion
of the control signal and a latch signal defined by a second
portion of the control signal.
9. The control circuitry of claim 8, further comprising a
compression module configured to receive, from the wafer probe,
data to be written to multiple locations on a computer memory
device.
10. The control circuitry of claim 9, wherein the compression
module is configured to replicate a single data bit to the multiple
memory locations during a write operation.
11. The control circuitry of claim 10, wherein the compression
module is configured to output a failure signal when data bits read
from the multiple memory locations have different values.
12. The control circuitry of claim 8, further comprising a second
input configured to receive from the wafer probe a testing signal
for indicating whether a testing operation by the wafer probe is a
read operation or a write operation.
13. The control circuitry of claim 12, further comprising a third
input configured to receive from the wafer probe a bank address, a
row address and a column address for activating a memory
location.
14. A device for testing a computer memory device, the testing
device comprising; clock circuitry configured to output a control
signal having a precharge signal defined by a first portion of the
control signal and a latch signal defined by a second portion of
the control signal; and a plurality of conductive pins, the
plurality of conductive pins having a control pin coupled to the
clock circuitry and configured to output the control signal to at
least one memory device.
15. The testing device of claim 14, wherein the plurality of
conductive pins comprises one hundred pins.
16. The testing device of claim 14, further comprising function
circuitry configured to output a second signal for selecting
whether a testing function by the testing device is a read testing
function or a write testing function.
17. The testing device of claim 14, wherein the plurality of
conductive pins is configured to concurrently align with bonding
pads of at least three memory devices.
18. The testing device of claim 17, further comprising read
circuitry configured to read data from each of the at least three
memory devices.
19. The testing device of claim 17, wherein the plurality of
conductive pins comprises at most nine address pins for each of the
at least three memory devices, wherein the address pins are
configured to output address bits to each of the at least three
memory devices.
20. The testing device of claim 17, further comprising compare
circuitry configured to compare data read from each of the at least
three memory devices with test data in order to test the integrity
of each of the at least three memory devices.
21. The testing device of claim 14, wherein the first portion of
the control signal is a leading edge of the control signal and the
second portion of the control signal is a trailing edge of the
control signal.
Description
RELATED APPLICATIONS
[0001] This present application is a continuation of U.S. patent
application Ser. No. 10/853,573, filed on May 25, 2004, which is a
continuation of U.S. patent application Ser. No. 09/653,112, filed
on Aug. 31, 2000, now U.S. Pat. No. 6,854,079, which is a
continuation-in-part application of U.S. patent application Ser.
No. 09/454,808, filed on Dec. 3, 1999, now U.S. Pat. No. 6,530,045,
issued on Mar. 4, 2003, each of which is hereby incorporated herein
by reference in its entirety.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates generally to semiconductor wafer
testing and more particularly to an apparatus and method for
reducing the pin count necessary to test Rambus dynamic random
access memory (RDRAM).
[0004] 2. Description of the Related Art
[0005] Rambus DRAM (RDRAM) is a general-purpose, high-performance,
packet-oriented dynamic random-access memory (DRAM) device suitable
for use in a broad range of applications, including computer
memory, graphics, video, and other applications. FIG. 1
schematically illustrates an RDRAM device 10 interconnected with a
central processing unit (CPU) 11 as part of a typical computer
system. The RDRAM device 10 receives clock signals 12, control
logic signal 14 and address information 16 from the CPU 11 via a
controller 20. Data 17 is written to and read from the RDRAM
10.
[0006] FIG. 2 is a block diagram illustrating one 144 Mbit RDRAM
configuration in the normal mode. The RDRAM comprises two major
blocks: a "core" block 18 comprising banks 22, sense amps 24 and
I/O gating 26 similar to those found in other types of DRAM
devices, and a control logic block in normal mode 19 which permits
an external controller 20 to access the core 18. The RDRAM core 18
is internally configured as 32 banks 22. Each bank 22 has 32,768
144-bit storage locations.
[0007] FIG. 3 is a diagram indicating that each of the banks 22 is
organized as 512 rows 28 by 64 columns 30 by 144 bits 32. The 144
bits 32 in each column 30 are serially multiplexed onto the RDRAM's
I/O pins as eight 18-bit words 34. The most significant bits 17-9
are communicated on I/O pins DQA <8:0>, and the least
significant bits 8-0 are communicated on the I/O pins DQB
<8:0>. The nine bits on each set of pins are output or input
on successive clock edges so that the bits in the eight words are
transferred on eight clock edges.
[0008] The control logic block 19 in FIG. 2 receives the CMD, SCK,
SIO0, and SIO1 strobes that supply the RDRAM configuration
information to the controller 10, and that select the operating
modes of the RDRAM device 10. The CFM, CFMN, CTM and CTMN pins
generate the internal clocks used to transmit read data, receive
write data, and receive the row and column pins used to manage the
transfer of data between the banks 22 and the sense amps 24 of the
RDRAM 10.
[0009] Address information 16 is passed to the RDRAM device 10 from
the CPU 11 via eight RQ pins 36 as illustrated in FIG. 4. The RQ
pins 36 are divided into two groups. Three ROW pins 38 are
de-multiplexed into row packets 40 that manage the transfer of data
between the banks 22 and the sense amps 24. Five COL pins 42 are
de-multiplexed into column packets 44 and manage the transfer of
data between the data pins and the sense amps 24 of the RDRAM 10.
More detailed information on the operation of RDRAM can be found in
Reference A, Direct RDRAM Preliminary Information, Document DL0059
Version 0.9 by Rambus Inc. which is incorporated herein by
reference.
[0010] Semiconductor chips, such as an RDRAM device 10, contain
circuit elements formed in the semiconductor layers which make up
the integrated circuits. FIGS. 5A and 5B illustrate a semiconductor
chip with exposed bonding pads 46 made of metal, such as aluminum
or the like that are formed as terminals of integrated circuits. In
normal operation, the control signals 14, the address signals 16,
and the data 17 are exchanged with the CPU 11 through connections
at these bonding pads 46.
[0011] In the manufacturing process, a large number of
semiconductor chips, each having a predetermined circuit pattern,
are formed on a semiconductor wafer 48 such as that shown in FIG.
6. FIG. 6 illustrates the semiconductor wafer 48 prior to being
diced into individual semiconductor chips. Although FIG. 6 only
shows a relatively small number of semiconductor chips on the
wafer, one skilled in the art will appreciate that many
semiconductor chips can be cut from a single wafer. The
semiconductor chips 10 are subjected to electrical characteristic
tests while they are on the wafer 48 through the use of a testing
apparatus, e.g., a wafer probe 50 having a plurality of pins 52.
Note that only the head of the wafer probe 50 is shown in FIG. 6.
Wafer probe testing is commonly used to quality sort individual
semiconductor chips before they are diced from the wafer 48. The
primary goal of wafer probe testing is to identify and mark for
easy discrimination defective chips early in the manufacturing
process. Wafer testing significantly improves manufacturing
efficiency and product quality by detecting defects at the earliest
possible stages in the manufacturing and assembly process. In some
circumstances, wafer probe testing provides information to enable
certain defects to be corrected.
[0012] FIG. 7 shows a plurality of the conductive pins 52 of the
wafer probe 50 of FIG. 6. The pins have respective tip ends 54
positionally adjusted to align with the bonding pads 48 of the
RDRAM device 10 to be tested. A wafer probe 50 has a limited number
of pins 52 (e.g., 100 pins) available to supply the test signals to
the RDRAM device 10 in the wafer 48. The RDRAM devices 10 could be
tested in their normal mode, but this would require in excess of 40
pins 52 on the wafer probe 50 to test each chip 10. Others have
recognized the benefits of creating a special test mode that
enables a semiconductor chip such as an RDRAM device 10 to be
tested with fewer pins. Therefore, one skilled in the art will
recognize that it is not required to have a pin 52 for every
bonding pad 48 on the chip 10. However, prior testing methodology
for RDRAM devices 10 requires at least 34 pins 52 on the wafer
probe 50 to test each RDRAM device 10. Consequently, the 100 pin
wafer probe is restricted to test, at most, two semiconductor chips
at one time. As a result, the production time and chip costs are
negatively impacted by this limitation.
[0013] As set forth above, the prior art method of wafer testing
RDRAM chips requires 34 pins 52 to test each RDRAM device 10, of
which 18 pins are address and data pins. Following this method, the
first operation in selecting the address on the RDRAM core entails
precharging the bank 22. Precharging is necessary because adjacent
banks 22 share the same sense amps 24 and cannot, therefore be
simultaneously activated. Precharging a particular bank 22
deactivates the particular bank and prepares that bank 22 and the
sense amps 24 for subsequent activation. For example, when the row
28 in the particular bank 22 is activated, the two adjacent sense
amps 24 are connected to or associated with that bank 22, and
therefore are not available for use by the two adjacent banks.
Precharging the bank 22 also automatically causes the two adjacent
banks to be precharged, thereby ensuring that adjacent banks are
not activated at the same time.
[0014] Selecting one of the 32 banks 22 to precharge requires five
address bits to specify the bank address. These address bits are
provided in a first control signal. The next operation in selecting
an address is activating a row 28 in a selected bank using a second
control signal. This operation requires nine address bits to select
one of the 512 rows 28, and five address bits to select one of the
32 banks 22, for a total of 14 address bits. The next operation
reads a column 30 in an open bank using a third control signal.
This operation requires five bank bits. This operation also
requires six column bits to select one of the 64 columns 30.
[0015] Reducing the number of address bits required to specify the
address location to be tested reduces the number of pin connection
52 required on the wafer probe 50 to test each individual RDRAM
device 10. Reducing the required number of pin connection 52
therefore allows more devices 10 to be tested at the same time,
thus permitting an important reduction in production time and chip
costs. As chip sizes continue to decrease, there is a corresponding
increase in the number of chips on each semiconductor wafer to be
tested. Therefore, the ability to test an increased number of
devices at the same time grows in importance.
SUMMARY OF THE INVENTION
[0016] The invention comprises a method of testing computer memory
devices, such as Rambus DRAM. The method requires fewer pin
connections to test each chip on a semiconductor wafer than
previously known methods. The test is performed on a semiconductor
wafer using a wafer probe. The number of pins required is reduced
by using a trailing edge of a precharge clock to latch the bank
address, thus eliminating the need to perform this function on a
later step. In combination with such use of the precharge clock's
trailing edge, the number of pins required is further reduced by
dividing the chip to be tested into a plurality of array cores and
compressing the output data so that only one data pin per array
core is required. By reducing the pin count, more DRAMs can be
tested at the same time, thus reducing the overall test cost and
time for testing a complete wafer.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017] FIG. 1 is a block diagram illustrating a RDRAM device as
part of a computer system.
[0018] FIG. 2 is a functional block diagram illustrating the RDRAM
chip configuration in the normal mode.
[0019] FIG. 3 is a conceptual drawing illustrating the RDRAM bank
configured in rows, columns, words, and bits in the normal
mode.
[0020] FIG. 4 is a conceptual drawing illustrating RQ pins
delivering the address information of FIGS. 1 and 2.
[0021] FIG. 5A is a top plan view of a RDRAM chip illustrating the
bonding pads.
[0022] FIG. 5B is a side elevation of the RDRAM of FIG. 5A.
[0023] FIG. 6 is a perspective view of a RDRAM semiconductor wafer
comprising a plurality of chips with a wafer probe.
[0024] FIG. 7 is a top plan view of the bonding pads of a RDRAM
chip aligned with the conductive pins which are connected to a
wafer probe.
[0025] FIG. 8 is a functional block diagram illustrating the RDRAM
chip configuration in the DFT mode.
[0026] FIGS. 9A and 9B are conceptual drawings, illustrating the
RDRAM bank configured in rows, columns, words, and bits and being
further divided so that the data from two rows can be compressed
for 2.times. row compression and output compressed into a single DQ
for DQ compression.
[0027] FIG. 10 is a block diagram illustrating the RDRAM core
divided up into four quadrants with a single DQ output after DQ
compression.
[0028] FIG. 11 is a timing diagram illustrating a typical write
cycle in the DFT mode.
[0029] FIG. 12 is a timing diagram illustrating a typical read
cycle in the DFT mode.
[0030] FIG. 13 is a timing diagram illustrating the compressed data
output for a DQ in a window manner showing a fault detection.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0031] The RDRAM in accordance with the invention has two modes of
operation: (1) a high speed packet mode for normal operation; and
(2) a low speed asynchronous mode for testing, which bypasses the
packetizing hardware, often called "design for test" circuits or
DFT. This second mode, shown as a block diagram in FIG. 8 is
realized by including DFT mode control logic 58 and data
compression logic 59 in the RDRAM device 10 to facilitate testing.
In one embodiment of the invention, in the DFT test mode, the RDRAM
behaves similar to an asynchronous DRAM, although data is still
input/output in bursts of eight.
[0032] As shown in FIG. 8, the RDRAM comprises three major blocks:
a "core" block 18, the control logic block in DFT mode 58 and the
Data Compression/Expansion Logic box 59. As shown in FIGS. 9A and
9B, the core 18 is internally configured as 32 banks 22 organized
as 512 rows 28 by 64 columns 30 by 144-bit storage locations. The
144 bits are multiplexed as eight 18-bit words. The core is further
divided for testing purposes as will be discussed below.
[0033] The DFT control logic 58 receives a number of signals from
the wafer probe 50, including, TestBSENSE, TestPRECH, TestWRITE,
TestCOLLAT, TestCLK_R/W, SIO0, SIO1, CMD, SCK and Burn PRECH_EN.
The Data Compression/Expansion Logic 59 compresses data so that
only four data pins are required, as will be discussed below.
[0034] The pins required for the DFT mode of operation are a subset
of the pins used in the normal mode of operation. Many of the
functions of the normal mode pins are redefined (as discussed
below) for the DFT mode. The mapping of the normal mode pins to the
DFT mode functions is illustrated below in Table 1. TABLE-US-00001
TABLE 1 DFT Pin Mapping Pin DFT Function SCK SCK CMD CMD
SIO<1:0> SIO<1:0> CFM/CTM TestClkR/W RQ<0>
TestBSENSE RQ<1> TestPRECH RQ<2> TestWrite RQ<3>
TestCOLLAT DQB<2:0> ADR<2:0> DQA<3:0>
ADR<6:3> DQB<3> ADR<7> DQB<6> ADR<8>
DQB<8> Burn PRECH_EN DQA<5:4> DQ<1:0>
DQB<5:4> DQ<3:2> CFMN/CTMN VCC/2 VCMOS VCMOS
[0035] To test a specific location in the core block 18 of the
RDRAM device 10, the location must be referenced by its bank
address, row address, and column address. In the normal
configuration of a 144 Mbit RDRAM device as illustrated in FIG. 3,
selecting the bank address of one of the 32 banks requires five
address bits, selecting a row address of one of the 512 rows in a
bank requires nine address bits, and selecting a column address of
one of the 64 columns in a bank requires six address bits. In
accordance with the present invention, the 144 Mbit RDRAM device is
wafer tested using DQ compression and 2.times. row compression.
[0036] In a further embodiment, a 288 Mbit RDRAM device can be
tested according to the invention as well. In the normal
configuration of a 288 Mbit RDRAM device, the RDRAM core block 18
is internally configured as 32 banks 22. Each bank 22 is organized
as 512 rows 28 by 128 columns 30 by 144 bits 32. Selecting the bank
address of one of the 32 banks requires five address bits,
selecting a row address of one of the 512 rows in a bank requires
nine address bits, and selecting a column address of one of the 128
columns in a bank requires seven address bits. In accordance with
the present invention, the 288 Mbit RDRAM device can be wafer
tested using either DQ compression or DQ compression and 2.times.
row compression.
[0037] In DQ compression, the RDRAM device 10 is divided into four
quadrants, 60A, 60B, 60C, and 60D, as illustrated in FIG. 10, with
each quadrant corresponding to a respective 36 megabit array core
61A, 61B, 61C, and 61D. Each array core 61A, 61B, 61C, and 61D is
an independent repair region. The lower two quadrants, 60A and 60B,
comprise banks 0-15. The upper two quadrants, 60C and 60D, comprise
banks 16-31. This division is based on physical design parameters
of the RDRAM device 10. The lower left quadrant 60A comprises bits
9-17 of banks 0-15. The lower right quadrant 60B comprises bits 0-8
of banks 0-15. The upper left quadrant 60C comprises bits 9-17 of
banks 16-31. The upper right quadrant 60D comprises bits 0-8 of
banks 16-31. As discussed below, for testing, only a single bit of
data is transferred into and out of each quadrant 60A, 60B, 60C,
and 60D. In particular, as will be discussed below, a data bit DQ0
is used to test the upper left quadrant 60C. A data bit DQ1 is used
to test the upper right quadrant 60D. A data bit DQ2 is used to
test the lower left quadrant 60A. A data bit DQ3 is used to test
the lower right quadrant 60B. Therefore, only four data bits are
required to test the entire memory. Note further that the upper
banks (16-31) and the lower banks (0-15) have separate data
connections in the DFT mode. Thus, the most significant bank bit
that distinguishes the upper and lower sets of banks is not
required, and the number of bank bits is reduced from five bits to
four bits.
[0038] In one embodiment of the invention using DQ compression and
2.times. row compression, the 2.times. row compression further
reduces the number of bank address bits required. In particular,
the data from corresponding rows in two alternating banks (e.g.,
bank n with bank n+2 and bank n+16 with bank n+18) are combined as
shown in FIGS. 9A and 9B so that the data are transferred to and
from both rows using a common DQ bit. This reduces the number of
selectable banks in each quadrant from sixteen to eight. Thus, only
three bank bits are required to select one of the eight banks in
each quadrant.
[0039] The data from the two rows of the alternating banks are
transferred (either written to the memory or read from the memory)
one byte at a time, as in the normal mode. However, because only
one data pin is available for each quadrant 60A, 60B, 60C, and 60D,
the nine bits of data from each of the two rows (18 bits of data in
all) in each quadrant are combined into a respective single bit
(i.e., DQ0, DQ1, DQ2, or DQ3). Thus, for each quadrant the data
from a column in the two rows are output as a sequence of eight
single data bits.
[0040] The compression of the data bits is performed by the data
compression/expansion logic 59. Each quadrant 60A, 60B, 60C, and
60D can have an associated data compression/expansion logic 59A,
59B, 59C, and 59D as illustrated in FIGS. 9A and 9B. Data are
written to the memory by applying a data bit to each of the
compressed data pins (i.e., to DQ0, DQ1, DQ2, DQ3). On each clock
edge the data compression/expansion logic 59 fans out the single
data bit to the eighteen data locations addressed by the bank, row
and column bits. Thus, the same data are written into all eighteen
locations. Thereafter, when the memory locations are read to test
the integrity of the memory, the data from the eighteen locations
read during each clock edge are compared to determine if any
location has a different data output. If the data are the same, the
output on the DQ line has a first constant state (e.g., a logic one
or a logic zero in accordance with the data written during the
write operation) to indicate pass. If any bit in any of the
eighteen locations is different, the data output on the DQ line is
forced to have a transition to indicate a failure.
[0041] In one embodiment for testing a 288 Mbit RDRAM device, the
result of the DQ compression and the 2.times. row compression is
that the array cores 61A, 61B, 61C and 61D are configured as 8
banks by 512 rows by 128 columns by eight four-bit bytes.
Therefore, only three bank select bits, nine row address bits, and
seven column address bits are required to identify a particular
location in the array core. This results in the ability to test
each RDRAM device 10 using only nine pins on the wafer probe 50 for
defining a specific address location. When the row is activated,
nine row address bits identify one of the 512 rows. When a column
in an open bank is read, the seven column bits identify the column
in the bank to be written to or read from.
[0042] FIG. 11 is a timing diagram that illustrates a typical write
cycle that is used to select the bank for row access and the bank
for column access, row address, column address, and strobe in the
data. FIG. 12 is a timing diagram that similarly illustrates a
typical read cycle. In FIGS. 11 and 12, address pins 64, 68, and 70
refer to subdivisions of the nine address pins used to identify a
particular location in the array core. Address pins 64 represent
Addr<8:6> (three address pins 8, 7, and 6). Address pins 68
represent Addr<5:1> (five address pins 5, 4, 3, 2, and 1).
Address pins 70 represent Addr<0> (one address pin 0).
[0043] In the write and read cycles depicted in FIGS. 11 and 12,
respectively, a precharge clock, TestPRECH 62, is used to select
the bank address. The leading edge of TestPRECH 62 is used to
precharge the bank designated by the bank address present on the
address pins 64. Precharging the bank prepares the bank and the
sense amps for activation. Since adjacent inner banks share the
same sense amps, adjacent banks cannot be activated at the same
time. Precharging any bank automatically causes adjacent banks to
be precharged also, thereby ensuring that adjacent banks are not
open at the same time. This happens in all modes of operation, not
just the DFT mode.
[0044] On the falling edge of TestPRECH 62, the bank corresponding
to the bank address on the address pins 64 is latched. This latched
bank address represents the bank that will be activated the next
time TestBSENSE is presented. Multiple banks can be active at any
one time. That is, banks previously activated and not subsequently
deactivated by precharging remain active in addition to the newly
activated bank. Precharging banks and latching banks are
accomplished using different edges of the same TestPRECH signal 62.
Thus, the present invention eliminates the need to provide separate
control signals for the precharge function and the latching
function.
[0045] Next, a row address is selected using address pins and a row
sense clock, TestBSENSE 66. TestBSENSE 66 causes the selected row
of the latched (i.e., active) bank to be sensed. The row address to
be sensed is the address present on the address pins 64, 68 and 70
at the falling edge of TestBSENSE 66. Because there are 512 rows,
nine address pins are required to select the row to be tested.
Because the bank was latched using the other edge of the TestPRECH
62, it is not required to select a bank in this operation. Thus,
unlike other known methods, the bank select bits do not have to be
applied at this time and only the nine address bits need to be
applied.
[0046] Data are then either read from or written to the column in
accordance with the address present on the address pins at the
rising edge of a column latch clock, TestCOLLAT 72. The row address
of the bank to be opened is presented on the falling edge of
TestBSENSE 66. The address of the column to be accessed is
presented on the rising edge of TestCOLLAT 72. In one embodiment of
the invention, if a new bank is to be opened, then the address of
that bank must be the same as the bank of the column to be
accessed. As a result, nine address bits are sufficient to provide
the necessary address bits to identify any location in the array
core.
[0047] In a further embodiment, the bank must be one of the banks
that was active when TestBSENSE 66 was applied. A TestWrite clock
74 determines whether the operation performed at TestCOLLAT 72 time
is a read or a write function. If TestWrite=1 at the rising edge of
TestCOLLAT 72, then the data present in a write buffer are written
to the RDRAM core. If TestWrite=0 at the rising edge of TestCOLLAT
72, then the data are read from the RDRAM core to a read
buffer.
[0048] FIGS. 11 and 12 show a TestClkR/W clock 76 strobing data
into the write buffer or out of the read buffer depending on the
state of TestWrite 74. If TestWrite=1, then data are input into the
write buffer from the tester on sequential edges of TestClkR/W 76,
beginning with the first falling edge. Eight clock edges transfer
data. It takes a total of six TesClkR/W 76 cycles to completely
load the write buffer. Additional clock cycles will initiate
another load sequence. A load sequence is not terminated until the
exact number of clock cycles are provided. If TestWrite=0, then
data are read from the read buffer to the external bus on each edge
of TestClkR/W 76, beginning with the second falling edge. Eight
clock edges transfer the data. It takes a total of six TestClkR/W
76 cycles to completely empty the read buffer. The chip under test
remains in the output mode until all data are read out of the read
buffer. Any additional clock cycles initiates a new read sequence.
Note that any transition on TestClkR/W 76 initiates a read or write
sequence depending on the state of TestWrite 74.
[0049] FIG. 13 is a timing diagram that illustrates the compressed
data being output in a window manner when reading the compressed
DQs. If the expected data is a "0", then the DQ will be low during
the entire window. A failure is indicated if the wrong data is
present, or if a data transition is detected during the window. If
the expected data is "1", then the DQ should remain high throughout
the window.
[0050] If a fault is indicated, it is not necessary to determine
which bit failed, it is sufficient to localize the fault to a row.
The tester has the capability to reconfigure the chip so that a
spare row is used to replace the row with the fault. The technology
for such reconfiguration is well known in the field.
[0051] Note that by reducing the required address bits to three and
by using both edges of the TestPRECH control signal, the maximum
number of address bits required is nine, which with the addition of
the four data bits, totals thirteen. This is significantly fewer
than the eighteen data and address bits used in other known test
methods.
[0052] Although specific implementations and operation of the
invention have been described above with reference to specific
embodiments, the invention may be embodied in other forms without
departing from the spirit or central characteristics of the
invention. The described embodiments are to be considered in all
respects only as illustrative and not restrictive. The scope of the
invention is indicated by the appended claims rather than by the
foregoing description. All changes which come within the meaning of
equivalency of the claims are to be embraced within their
scope.
* * * * *