CA1169962A - Dynamic random access memory - Google Patents
Dynamic random access memoryInfo
- Publication number
- CA1169962A CA1169962A CA000378895A CA378895A CA1169962A CA 1169962 A CA1169962 A CA 1169962A CA 000378895 A CA000378895 A CA 000378895A CA 378895 A CA378895 A CA 378895A CA 1169962 A CA1169962 A CA 1169962A
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- Canada
- Prior art keywords
- voltage state
- bit lines
- voltage
- state
- bit line
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Classifications
-
- G—PHYSICS
- G11—INFORMATION STORAGE
- G11C—STATIC STORES
- G11C11/00—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor
- G11C11/21—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements
- G11C11/34—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices
- G11C11/40—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors
- G11C11/401—Digital stores characterised by the use of particular electric or magnetic storage elements; Storage elements therefor using electric elements using semiconductor devices using transistors forming cells needing refreshing or charge regeneration, i.e. dynamic cells
- G11C11/4063—Auxiliary circuits, e.g. for addressing, decoding, driving, writing, sensing or timing
- G11C11/407—Auxiliary circuits, e.g. for addressing, decoding, driving, writing, sensing or timing for memory cells of the field-effect type
- G11C11/409—Read-write [R-W] circuits
- G11C11/4094—Bit-line management or control circuits
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- Engineering & Computer Science (AREA)
- Microelectronics & Electronic Packaging (AREA)
- Computer Hardware Design (AREA)
- Dram (AREA)
Abstract
DYNAMIC RANDOM ACCESS MEMORY
ABSTRACT OF THE DISCLOSURE
A dynamic random access memory (10) receives a memory address of a row decoder (14) which charges a selected row line (18). When the row line (18) is charged an access transistor (24) in a memory cell (22) is rendered conductive to connect a storage capacitor (26) to a bit line (30). The bit lines (30, 38) are previously set at an equilibration voltage.
The voltage on the bit line (30) is driven slightly above the equilibration voltage if a high voltage state had been stored in the capacitor (26) or the voltage on the bit line is driven slightly below the equilibration voltage if a low voltage state had been stored on the capacitor (26). A sense amplifier (44) is connected to the bit lines (30, 38) and upon receipt of a latch signal (L) drives the one of the bit lines (30, 38) having the lower voltage to a low voltage state. A pull-up circuit (60) drives the voltage on the remaining bit line of the pair to a high voltage state, restoring the memory storage capacitor (26) to its initial state. After the row line (18) is now discharged trapping the original data state in the.
storage capacitor (26), precharge transistors (50, 52) then connect together the bit lines (30, 38) through a latch node (46) to share charge between the bit lines (30, 38) and drive the bit lines (30, 38) to the equilibration voltage.
ABSTRACT OF THE DISCLOSURE
A dynamic random access memory (10) receives a memory address of a row decoder (14) which charges a selected row line (18). When the row line (18) is charged an access transistor (24) in a memory cell (22) is rendered conductive to connect a storage capacitor (26) to a bit line (30). The bit lines (30, 38) are previously set at an equilibration voltage.
The voltage on the bit line (30) is driven slightly above the equilibration voltage if a high voltage state had been stored in the capacitor (26) or the voltage on the bit line is driven slightly below the equilibration voltage if a low voltage state had been stored on the capacitor (26). A sense amplifier (44) is connected to the bit lines (30, 38) and upon receipt of a latch signal (L) drives the one of the bit lines (30, 38) having the lower voltage to a low voltage state. A pull-up circuit (60) drives the voltage on the remaining bit line of the pair to a high voltage state, restoring the memory storage capacitor (26) to its initial state. After the row line (18) is now discharged trapping the original data state in the.
storage capacitor (26), precharge transistors (50, 52) then connect together the bit lines (30, 38) through a latch node (46) to share charge between the bit lines (30, 38) and drive the bit lines (30, 38) to the equilibration voltage.
Description
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~,~77 -DYNAMIC RANDOM ACCESS MEMORY
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TECHNICAL FIELD
: ~ The present invention pertains to semiconductor : integrated circuits and in particular to a random access memory which utilizes dynam:ic memory cells.
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~ ~ 6~2 r BACRGROUND ART
The operation of previous dynamic random access memory circuits is described in U.S. Pat~nt No. 3,588,844 and 3,514,765 to Christeneon, U.S. Patent No. 3,699,537 S to Wahlstrom and V.S. Patent No. 3,902,082 and 3,969,706 to Proebsting et al. As shown in the Wahlstrom and Proebsting Patents, it has been the practice to use sense amplifiers to detect voItage differentials on bit lines which have had memory cells connected thereto. The }0 ` connection of the memory cell to the bit line changes the previously established voltage on the bit line to estabish the desired data state as a voltage differential on the bit lines. However, the voltage change on a bit line caused by the connection of a memory cell thereto lS is very smali and ~he detection of such a small voltage - change has presente~ a serious problem in the design , of dynamic random access memories. A further problem is that electrical noise can be picked up by the bit lines and his noise can mask the desired voltage offset 20 ~ produced by a memory cell. Further, integrated circuit fabrication tolerances can result in unbalanced bit lines which also interere with the reading of a memory cell.
In respo~se~to these problems, it has heretofore been the practice to incorporate a dummy cell with each blt 1ine of the memory. The dummy cells are precharge~
o a given voltage state and are connec~ed during each memory cycle~to the nonselected bit line within each pa~ir of bit lines. However, the inclusion of a large number of: dummy cells :together with their associated 30~ circuitry in~reases~the si e of the integrated circuit and adds to the ~ircu~t complexity.
In view of the above problems, there exists a need for a dynami~ ran~om access memory which operates in ~such a method so as not to require-a dummy cell for 35 ~ each bit line while at ~he same time p~viAing reliable identification~of the voltage states stored in the -~ memory cells.
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~`.: ) ~)ISCLOSURE OF THE INVENTION
The present invention provides a method for operating a dynamic random access memory in the following steps. A
high or low voltage state is stored in a dynamic S memory cell where the high vvltage state corresponds to a first data state and the low voltage state corresponds to a second data state. The memory cell is then connected to one of a pair of bit lines after the bit lines have been set to an intermediate voltage state. When a memory cell storing a low voltage is connected to the bit line, the voltage on the bit line is decreased. When a memory cell storing a high voltage is connected to the bit line, the voltage on the bit line is increased.
When the voltage state on one bit line is being changed 15 by the connection of a memory cell thereto, the ~
complementary bit line of the pair of bit lines is maintained essentially at the intermediate voltage ~
state which had been set thereon. After the ~emory cell ; has been connected to one of the bit lines, the bit 20~ 1ine h~aving the~lowest voltage thereon is driven to à low voltage~state~, and the other of the bit lines is driven to a~ hlgh voltage state. The memory cell lS
disconnected ~rom the correspondi~g ~bit line after the corresponding~bit line~has been~driven to either the low 25~ ~voltage ~tate or the high ~oltage state. After the mèmory~cell has been disconnected from the corresponding bit l~ine,~the b~its lines are connected together to equilibrate the voltages~on the bit lines to establlsh the intermediàte~voltage state in preparation for a new `30~ ~cycle.
99~2 BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention and the advantages thereof, reference is now ~ade to the following description taken in conjunction 5 with the accompanying drawings in which:
FIGURE 1 is a schematic îllustration of the dynamic random access memory in accordance with the present invention; and FIGURE 2 is a set of timing diagrams illustrating the various signals which occur in the dynamic random access memory illustrated in FIGURE 1.
FIGURE 3 is a schematic illustration of the sense amplifier shown in FIGURE 1; and FXGURE 4 is a schematic illustration of the pull-up 15: circuit shown in FIGURE 1.
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~ :~ 6~3962 DETAILED DESCRIPTION OF THE INVENTION
The dynamic random access memory of the present invention is illustrated in FIGURE 1. A memory address is provided to the memory 10 through a group of address lines 12. The address lines 12 are provided to each of a plurality of row decoders such as row decoder 14. The address lines 12 are also connected to each of a plurality of column decoders such as decoders 16 and 17. The address bits for the selected row line are provided in parallel fashion through lines 12 at one time in the memory cycle and the address bits for the selected column are provided through lines 12 at a later time in the : memory cycle. This is illustrated by the address waveform : indicated as Ao~An shown in FIGURE 2.
15 ~ The row address bits select a row decoder such as :
~ 14 which in turn activates a row line 18.- The row line : ~ 18 is connected to a dynamic memory cell 22 which comprises an access transistor 24 and a storage capacitor ~ 6. The gate terminal of transistor 24 is connected to :: : 20 the row line 18 and the source terminal of the a~c:ess ::transistor is connected to a first terminal of capacitor 26. The remaining: terminal of capacitor 26 is connected ` to~a ground node 28. The drain terminal of access :transistor 24 is connected:to a bit line 30.
25~ ~ A~row line 20 is charged by a row decoder 21 and is connected to a dynamic me~ory cell 32 which comprises an access transistor 34 and~a~storage capacitor 36. The , : : gate terminal of transistor 34 is:~connected to ~he row ;line 20 and the sour~e~terminal thereof is connected ;30 to a first terminal of the:~capacitor 36. The remaining te~rminal of:capacitor 36 is:connected to the ground node : 28.~ The~drain ter~inal of:transistor 34 is connected ~ :
to a bit ~Iine 38 .: ~ ~ ~
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When row line 18 is driven to a high v~ltaye state the corresponding access transistor 24 is a~tivated to provide a conductive path between the bit line 30 and the storage capacitor 26. The voltage on a row line S selected by a row decoder is illustrated by the timing signal 40 shown in FIGURE 2. The sense amplifier 44 is activated in response to a latch signal which is transmitted through a latch node 46. The latch signal L is illustrated in FIGURE 2 as waveform 48.
The memory 10 includes an equilibration circuit which ~ comprises transistors 50 and 52 wherein transistor 50 : ~ has the source and drain terminals thereof connected : ~ between bit line 30 ~nd latch nod 46 and transistor 52 has:the source and drain terminals thereof connected : 15: between bit line 38 and the latch node 46. The gate terminals of:transistors 50 and 52 are:connected to a ~: ~ : node~-54 wh:ich receive an equilibration signal E. ; The equilibration~signal E is illustrated in FIGURE 2 as wave~orm~56. When the equilibratio~n signal E is at ~ :
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~,~77 -DYNAMIC RANDOM ACCESS MEMORY
.
.
TECHNICAL FIELD
: ~ The present invention pertains to semiconductor : integrated circuits and in particular to a random access memory which utilizes dynam:ic memory cells.
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~ ~ 6~2 r BACRGROUND ART
The operation of previous dynamic random access memory circuits is described in U.S. Pat~nt No. 3,588,844 and 3,514,765 to Christeneon, U.S. Patent No. 3,699,537 S to Wahlstrom and V.S. Patent No. 3,902,082 and 3,969,706 to Proebsting et al. As shown in the Wahlstrom and Proebsting Patents, it has been the practice to use sense amplifiers to detect voItage differentials on bit lines which have had memory cells connected thereto. The }0 ` connection of the memory cell to the bit line changes the previously established voltage on the bit line to estabish the desired data state as a voltage differential on the bit lines. However, the voltage change on a bit line caused by the connection of a memory cell thereto lS is very smali and ~he detection of such a small voltage - change has presente~ a serious problem in the design , of dynamic random access memories. A further problem is that electrical noise can be picked up by the bit lines and his noise can mask the desired voltage offset 20 ~ produced by a memory cell. Further, integrated circuit fabrication tolerances can result in unbalanced bit lines which also interere with the reading of a memory cell.
In respo~se~to these problems, it has heretofore been the practice to incorporate a dummy cell with each blt 1ine of the memory. The dummy cells are precharge~
o a given voltage state and are connec~ed during each memory cycle~to the nonselected bit line within each pa~ir of bit lines. However, the inclusion of a large number of: dummy cells :together with their associated 30~ circuitry in~reases~the si e of the integrated circuit and adds to the ~ircu~t complexity.
In view of the above problems, there exists a need for a dynami~ ran~om access memory which operates in ~such a method so as not to require-a dummy cell for 35 ~ each bit line while at ~he same time p~viAing reliable identification~of the voltage states stored in the -~ memory cells.
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~`.: ) ~)ISCLOSURE OF THE INVENTION
The present invention provides a method for operating a dynamic random access memory in the following steps. A
high or low voltage state is stored in a dynamic S memory cell where the high vvltage state corresponds to a first data state and the low voltage state corresponds to a second data state. The memory cell is then connected to one of a pair of bit lines after the bit lines have been set to an intermediate voltage state. When a memory cell storing a low voltage is connected to the bit line, the voltage on the bit line is decreased. When a memory cell storing a high voltage is connected to the bit line, the voltage on the bit line is increased.
When the voltage state on one bit line is being changed 15 by the connection of a memory cell thereto, the ~
complementary bit line of the pair of bit lines is maintained essentially at the intermediate voltage ~
state which had been set thereon. After the ~emory cell ; has been connected to one of the bit lines, the bit 20~ 1ine h~aving the~lowest voltage thereon is driven to à low voltage~state~, and the other of the bit lines is driven to a~ hlgh voltage state. The memory cell lS
disconnected ~rom the correspondi~g ~bit line after the corresponding~bit line~has been~driven to either the low 25~ ~voltage ~tate or the high ~oltage state. After the mèmory~cell has been disconnected from the corresponding bit l~ine,~the b~its lines are connected together to equilibrate the voltages~on the bit lines to establlsh the intermediàte~voltage state in preparation for a new `30~ ~cycle.
99~2 BRIEF DESCRIPTION OF THE DRAWINGS
For a more complete understanding of the present invention and the advantages thereof, reference is now ~ade to the following description taken in conjunction 5 with the accompanying drawings in which:
FIGURE 1 is a schematic îllustration of the dynamic random access memory in accordance with the present invention; and FIGURE 2 is a set of timing diagrams illustrating the various signals which occur in the dynamic random access memory illustrated in FIGURE 1.
FIGURE 3 is a schematic illustration of the sense amplifier shown in FIGURE 1; and FXGURE 4 is a schematic illustration of the pull-up 15: circuit shown in FIGURE 1.
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~ :~ 6~3962 DETAILED DESCRIPTION OF THE INVENTION
The dynamic random access memory of the present invention is illustrated in FIGURE 1. A memory address is provided to the memory 10 through a group of address lines 12. The address lines 12 are provided to each of a plurality of row decoders such as row decoder 14. The address lines 12 are also connected to each of a plurality of column decoders such as decoders 16 and 17. The address bits for the selected row line are provided in parallel fashion through lines 12 at one time in the memory cycle and the address bits for the selected column are provided through lines 12 at a later time in the : memory cycle. This is illustrated by the address waveform : indicated as Ao~An shown in FIGURE 2.
15 ~ The row address bits select a row decoder such as :
~ 14 which in turn activates a row line 18.- The row line : ~ 18 is connected to a dynamic memory cell 22 which comprises an access transistor 24 and a storage capacitor ~ 6. The gate terminal of transistor 24 is connected to :: : 20 the row line 18 and the source terminal of the a~c:ess ::transistor is connected to a first terminal of capacitor 26. The remaining: terminal of capacitor 26 is connected ` to~a ground node 28. The drain terminal of access :transistor 24 is connected:to a bit line 30.
25~ ~ A~row line 20 is charged by a row decoder 21 and is connected to a dynamic me~ory cell 32 which comprises an access transistor 34 and~a~storage capacitor 36. The , : : gate terminal of transistor 34 is:~connected to ~he row ;line 20 and the sour~e~terminal thereof is connected ;30 to a first terminal of the:~capacitor 36. The remaining te~rminal of:capacitor 36 is:connected to the ground node : 28.~ The~drain ter~inal of:transistor 34 is connected ~ :
to a bit ~Iine 38 .: ~ ~ ~
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When row line 18 is driven to a high v~ltaye state the corresponding access transistor 24 is a~tivated to provide a conductive path between the bit line 30 and the storage capacitor 26. The voltage on a row line S selected by a row decoder is illustrated by the timing signal 40 shown in FIGURE 2. The sense amplifier 44 is activated in response to a latch signal which is transmitted through a latch node 46. The latch signal L is illustrated in FIGURE 2 as waveform 48.
The memory 10 includes an equilibration circuit which ~ comprises transistors 50 and 52 wherein transistor 50 : ~ has the source and drain terminals thereof connected : ~ between bit line 30 ~nd latch nod 46 and transistor 52 has:the source and drain terminals thereof connected : 15: between bit line 38 and the latch node 46. The gate terminals of:transistors 50 and 52 are:connected to a ~: ~ : node~-54 wh:ich receive an equilibration signal E. ; The equilibration~signal E is illustrated in FIGURE 2 as wave~orm~56. When the equilibratio~n signal E is at ~ :
2~0;~bigh~voltage state~the transistors 50 and 52 are turned on~thereby connecting~the bit lines 30 and 38 to node -A:~pull-up~circuit 60 is connected to the bit line
3~hrough a line~62:.~ The pull-up~circuit 60 operates 25~ in~response:~to~prech~a~rge:signals P, P0 and P1 which are Ilu~trated::~respect~ive:ly~as:wave~orms 63, 64 and 66 in FIGURE~2. :A~similar:pull-up circuit 68 is connected to bit line:38~thrQugh~line 70~ Pull:-up circuits ~0 and 68 d~etect~when~the voltag~e:on the~corresponding bit line : 3~ is~above:a~:pre:set vol:tage level and, upon receipt of the:precharge~signals~j:pulls the~it lin~ up to the supply voltage:,~as:described~below.
Each~of~the blt~ ne~s~ia provided with a column transistor fQr:routing da~a states~:into and out of the 35~: memory cells.~ Column transistor 74 has the source and , :
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drain terminals thereof connected between bit line 30 and an input/output line 76. The gate terminal of column transistor 74 is connected to the column decoder 16. Likewise, a column transistor 80 has the drain and source terminals thereof connected between bit line 38 and an input/output line 82. The gate terminal of column transistor 80 is connected to the column decoder 17 which responds to the same column address as does column decoder 16. The column decoders I6 and 17 activate selected column transistors in response to the column address bits received through address lines 12 to transfer data states to and from an addressed memory cell.
The input/output lines 76 and 82 are connected to an input/output circuit 84 which serves to transfer the data states which are written into and read from he memory cells. The data states are received fro~ external~
circuitry through a data input terminal 86 and transmitted to external circuitry through a data output terminal 87 The operation of the dynamic random access memory 10 of the p~esent invention is now described in reference to~FIGURES 1-4. It is assumed that this circuit operates wi~th~a 5.0 volt power supply. ~A memory cycle is initiated by~a row address strobe~(RAS) signal 90 wh ich goes to an active~state~in a transition from~a high level to a 25~ low level.~ The~row address~bits~ are supplied to the row decoder~14 as~ind~icated by the reference numeral g2a.
The row addr~ess bits~are received shortly after the RAS
s~ignal goes to~the aotive state. ~he row decoder 14 routes the row~enable signal 40 to the selected row line.
30~ When the row enable signaI 40 goes to the five volt level~the access transistor 24 in memory cell 22 is rendered conduc~tive to connect the'storage capacitor 26 ~o the bit line 30~ The bit lines 3D and 38 have `prevlously~been equillbrated to the voltage level of 35~ approximately 2.0~volts as shown~by waveform 96. If ~- , :
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capacitor 26 has previously had a 5.0 volt level s~ored therein, bit line 30 would be driven to approximately 2.3 volts as indicated by waveform 96a in FI~URE 2, due to charge sharing between the capacitor 26 and bit line 30. But if the capacitor 26 has previously been discharged to ground the bit line 30 will be pulled to approximately 1.8 volts as indicated by waveform 96b.
After the memory cell 22 has been connected to the bit line 30 the latch signal L shown as waveform 48 is pulled to ground potential. The sense amplifier 44 responds to the latch signal by pulling to ground potential the one of the bit lines connected thereto which is at the lower voltage. If capacitor 26 has previously been discharged the voltage on bit line 30 lS will be that shown in waveform 96b where the voltage is pulled to ground potential. But if the storage capacitor 26 has~had a high voltage level stored therein, as shown in waveform 96a, bit line 30 will not be affected by the operation of sense amplifier 44.
20 ~ ut~if bit~line 30 has~been elevated in voltage shown by waveform 96a, it exceeds the bit line 38 voltage, shown as waveform 98,~so that bit line~38 will~be pulled to ground as~shown~by~waveform 98a. But lf the;voltage on b~it~lin~e 3~0~had~been~pulled down by the storage capacitor 2~5~ 26 the equilibration voltage on bit line 38 would not ~-b~e~afected by~the~sense amplifier~44. This condition is indicated~in~waveform 98b.~
A~ter the~ sense ~ampliier 44 has pulled one of the bit~ nes to~ground and;after;~he precharge signal P
3Q ~ has~precharged the pullup circuits~60 and 68, the pr~echa~rge~signals,~PO and~Pl are received to actlvate he pull up circuits &0 and 68. ~The pull up circuits d~etect~whlch one~of~the bit lines~has a voltage thereon ;above~a~prese~ voltage. One~ of the bit lines will be àt ground potenti`al and the other o the bit lines will ~ ~ ~99~2 .
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be at either the equilibration voltage or at the elevated voltage caused by connecting a storage capacitor having a high voltage stored therein. The bit line with the high - voltage thereon will be pulled up to the supply voltage.
For the-bit lines which received a high charge from the storage cell this is indicated by waveform 96a and for the bit line which was at the e~uilibration voltage this is indicated by waveform 98b. At this time the storage capacitor which had been connected to the bit line has been restored to its original voltage.
When one of the bit lines has been driven to the supply voltage and the other ~it line has been pulled to ground the column transistors 74 and 80 are turned on to connect the bit lines 30 and 38 ~o the input/output lines 75 and 82 respectively. The voltage states on the bit lines are transferred through the input/output lines to the inputjoutput circuit 84 which has a sense amplifier therein to detect the voltage differential between the input/output lines 76 and 820 ~The sense amplifier in the ~20 input/output circuit determines the voltage state which is stored in the memory cell and transfers this voltage state through the~data output line 87.
After one o the bit lines has been pulled to ground~and the other bit line has been pulled to the 25~ supply voltage,~the data state in the memory cell has been restored, and the row line 18 is returned ~o ground to isolate the char~e on the storage capacitor. The ; bit lines are then~permitted to~float. The equilibration ~signal 56 is then applied to the gate `terminals of 30 ~ ~transistors 50 and 52 to render these transistors con~uctive and connect bit line 30 to bit line 38 through latch node 46. This connection permits the charge on the bit~lines~to be shared such th~at the bit lines eguilibrate to a voltage approxima~ely midway between 35; ~he supply voltage and ground. This is indicated in both of the waveforms 96 and 98 where the waveforms are returned to the equilibration voltage of two vo~ts.
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A representative circuit for the sense amplifier 44 shown in FIGURE 1 is illustrated in FIGURE 3. A
pass transistor 104 has the source and drain terminals - thereof connected between bit line 30 and a node 106.
A second pass transistor 108 has a source and drain terminals thereof connected between bit line 38 and a node 110. The gate terminals of both transistors 104 and 108 are connected to a high voltage, such as the supply voltage V~c. Transistors 104 and 108 are always conductive and functi~n as resistors. A
transistor 112 has the drain terminal thereof connected to node 106 and the source terminal thereof connected to the latch node 46. The gate terminal of tr~nsistor 112 is connected to node 110. A transistor 114 has the drain terminal thereof connected to node 110, the source terminal thereof connected to node 46 and the gate terminal thereof connected to node ln6 ~ The sense`amplifier operation occurs after a memory cell has been connected to one of the bit lines, either ~20 30 or 38. One of the bit lines is then at a higher voltage than the other bit line. Assume, for example~
that bit llne 30 is at the higher voltage. When the . ~ latch signal~slowly~pulls node 4~ to ground, transistor ~; 114 will be turned on before transistor 112 because the gate to source bias on transistor 114 is greater han the gate to source bias on transistor 112. As transistor 114 is rendered conductive node 110 will be discha~rged through transistor 114 into the latch node 46. As node~ll0 is discharged the gate bias on transistor 30~ ;112~is 1owered~thus~preventing transistor 112 from being rendered conductive~ When the latch signal is pulled all the ~way to ground transistor 114 will continue ~to be conduc~ive since bit line 30 and node 106 remain at : , ' ~ ' : :
I .'~ l~9g~2 the previous high charge state. As node 110 is discharged, conduction through transistor 108 discharges bit line 38. Thus, after the latch signal has gone completely to ground bit line 38 will also be pulled S to ground.
If bit line 38 is at a higher voltage after a memory cell is connected to one of the bit lines, transistor 112 will be rendered conductive to discharge node 106 and pull bit line 30 to ground.
: 10 A schematic illustration for the pull-up circuits 60 and 68 is given in FIGURE 4. A transistor 120 has the drain terminal thereof connected to Vcc, the source terminal thereof connected to a node 122 and the :
gate terminal thereof connected to receive the precharge ~15 signal Pr A transistor 124 has the drain terminal thereof ; :connected to node I22, the source terminaI thereof connected to bit line 30 and:the gate terminal thereof connected to receive the precharge signal P0.
: : A transistor 126 has the drain terminal thereof 20 ~ connected~to receive the precharge signal Pl, the gate terminal thereof connected to node 122 and the source terminal thereof connected to the gate terminal of a~transistor:128. The drain terminal o transistor : 128~is c:onnecte~ to the trcc~and the source terminal 25~ thereof~:is connected to bit~line~30.
:When~the precharge~signal P is received trans:istor 20:îs:rendered conductive to precharge node 122 to a~high~oltag~state. Once~the:~precharge signal returns to a~:low:voltag~ level the~node 122 is left floating 30~ :at the~;high~voltage ~talte.~ When the precharge signal P~ goes to approximately 2 ~olts, transistor 124 is rendered~onductive if the~bit line 30 is at a ufficiently:low voltage state:such that there is at least one~;`transistor threshold voltage between the gate ; 3~5 ~and source terminals of transistor 124. If transistor : :`:: ~ :
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124 is rendered conductive node 12~ is discharged into the bit line 30.
But if the charge on bit line 30 is sufficiently high so that there is less than one transistor threshold voltage between the gate and source terminals of transistor 124, transistor 124 will not be rendered conductive by the precharge signal P0, leaving node 122 floating at a high voltage level. The Pl signal is then applied to the drain terminal of transistor 126. If node 122 is at a high voltage, transistor 126 is conductive so that the source of transistor 126 follows signal P1 - above Vcc. This is possible since the channel capacitance ~ of transistor 126 bootstraps node 122 to a hiyh voltage ; level. With the full voltage level of bootstr~pped precharge signal Pl applied to the gate ter~inal of transistor 128, the full supply voltage Vcc is applied to the bit line 3n, thereby pulling the bit line to the voltage state of Vcc. Thus when the voltage on the bit line 30 îs abov~ a preset level, the bit line will be elevated to the supply voltage by opera~ion of the precharge circuit 60, but if the vol~age on the bit line 30 is less than a preset level, the precharge circuit 60 will have~no effect upon the bit line 30.
In ~summary,~the present invention comprises a ~dynamic random~access memory in which bit lines are equilibrated to approximately one half of the supply vol~tage before a memory cell is connec~ed thereto. A
sense amplif~ier detects the voltage dif~erence on the bit lines caused by the connection of the storage ~capacitor to one of the bit lines and pulls the bit line having~a~lower voltage thereon to ground~ A
pull up circult elevates the bit line having the greater voltage thereon~ Af~er the voltage state is transferred ~hrough input~output lines and after the memory cell i5 isolated, the bit lines are permit~ed to float and are 1 ~ 699~
;' ~ ! ) connected together through a latch node so that the bit lines are returned to the equilîbration voltage as a result of charge transfer between the bit lines.
Although one embodiment of the invention has been illustrated in the accompanying drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications and substitutions without departiny from the scope of the invention.
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Each~of~the blt~ ne~s~ia provided with a column transistor fQr:routing da~a states~:into and out of the 35~: memory cells.~ Column transistor 74 has the source and , :
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drain terminals thereof connected between bit line 30 and an input/output line 76. The gate terminal of column transistor 74 is connected to the column decoder 16. Likewise, a column transistor 80 has the drain and source terminals thereof connected between bit line 38 and an input/output line 82. The gate terminal of column transistor 80 is connected to the column decoder 17 which responds to the same column address as does column decoder 16. The column decoders I6 and 17 activate selected column transistors in response to the column address bits received through address lines 12 to transfer data states to and from an addressed memory cell.
The input/output lines 76 and 82 are connected to an input/output circuit 84 which serves to transfer the data states which are written into and read from he memory cells. The data states are received fro~ external~
circuitry through a data input terminal 86 and transmitted to external circuitry through a data output terminal 87 The operation of the dynamic random access memory 10 of the p~esent invention is now described in reference to~FIGURES 1-4. It is assumed that this circuit operates wi~th~a 5.0 volt power supply. ~A memory cycle is initiated by~a row address strobe~(RAS) signal 90 wh ich goes to an active~state~in a transition from~a high level to a 25~ low level.~ The~row address~bits~ are supplied to the row decoder~14 as~ind~icated by the reference numeral g2a.
The row addr~ess bits~are received shortly after the RAS
s~ignal goes to~the aotive state. ~he row decoder 14 routes the row~enable signal 40 to the selected row line.
30~ When the row enable signaI 40 goes to the five volt level~the access transistor 24 in memory cell 22 is rendered conduc~tive to connect the'storage capacitor 26 ~o the bit line 30~ The bit lines 3D and 38 have `prevlously~been equillbrated to the voltage level of 35~ approximately 2.0~volts as shown~by waveform 96. If ~- , :
~ ~ 9 $ rJ
capacitor 26 has previously had a 5.0 volt level s~ored therein, bit line 30 would be driven to approximately 2.3 volts as indicated by waveform 96a in FI~URE 2, due to charge sharing between the capacitor 26 and bit line 30. But if the capacitor 26 has previously been discharged to ground the bit line 30 will be pulled to approximately 1.8 volts as indicated by waveform 96b.
After the memory cell 22 has been connected to the bit line 30 the latch signal L shown as waveform 48 is pulled to ground potential. The sense amplifier 44 responds to the latch signal by pulling to ground potential the one of the bit lines connected thereto which is at the lower voltage. If capacitor 26 has previously been discharged the voltage on bit line 30 lS will be that shown in waveform 96b where the voltage is pulled to ground potential. But if the storage capacitor 26 has~had a high voltage level stored therein, as shown in waveform 96a, bit line 30 will not be affected by the operation of sense amplifier 44.
20 ~ ut~if bit~line 30 has~been elevated in voltage shown by waveform 96a, it exceeds the bit line 38 voltage, shown as waveform 98,~so that bit line~38 will~be pulled to ground as~shown~by~waveform 98a. But lf the;voltage on b~it~lin~e 3~0~had~been~pulled down by the storage capacitor 2~5~ 26 the equilibration voltage on bit line 38 would not ~-b~e~afected by~the~sense amplifier~44. This condition is indicated~in~waveform 98b.~
A~ter the~ sense ~ampliier 44 has pulled one of the bit~ nes to~ground and;after;~he precharge signal P
3Q ~ has~precharged the pullup circuits~60 and 68, the pr~echa~rge~signals,~PO and~Pl are received to actlvate he pull up circuits &0 and 68. ~The pull up circuits d~etect~whlch one~of~the bit lines~has a voltage thereon ;above~a~prese~ voltage. One~ of the bit lines will be àt ground potenti`al and the other o the bit lines will ~ ~ ~99~2 .
.
be at either the equilibration voltage or at the elevated voltage caused by connecting a storage capacitor having a high voltage stored therein. The bit line with the high - voltage thereon will be pulled up to the supply voltage.
For the-bit lines which received a high charge from the storage cell this is indicated by waveform 96a and for the bit line which was at the e~uilibration voltage this is indicated by waveform 98b. At this time the storage capacitor which had been connected to the bit line has been restored to its original voltage.
When one of the bit lines has been driven to the supply voltage and the other ~it line has been pulled to ground the column transistors 74 and 80 are turned on to connect the bit lines 30 and 38 ~o the input/output lines 75 and 82 respectively. The voltage states on the bit lines are transferred through the input/output lines to the inputjoutput circuit 84 which has a sense amplifier therein to detect the voltage differential between the input/output lines 76 and 820 ~The sense amplifier in the ~20 input/output circuit determines the voltage state which is stored in the memory cell and transfers this voltage state through the~data output line 87.
After one o the bit lines has been pulled to ground~and the other bit line has been pulled to the 25~ supply voltage,~the data state in the memory cell has been restored, and the row line 18 is returned ~o ground to isolate the char~e on the storage capacitor. The ; bit lines are then~permitted to~float. The equilibration ~signal 56 is then applied to the gate `terminals of 30 ~ ~transistors 50 and 52 to render these transistors con~uctive and connect bit line 30 to bit line 38 through latch node 46. This connection permits the charge on the bit~lines~to be shared such th~at the bit lines eguilibrate to a voltage approxima~ely midway between 35; ~he supply voltage and ground. This is indicated in both of the waveforms 96 and 98 where the waveforms are returned to the equilibration voltage of two vo~ts.
:: :
9 ~ ~
.
A representative circuit for the sense amplifier 44 shown in FIGURE 1 is illustrated in FIGURE 3. A
pass transistor 104 has the source and drain terminals - thereof connected between bit line 30 and a node 106.
A second pass transistor 108 has a source and drain terminals thereof connected between bit line 38 and a node 110. The gate terminals of both transistors 104 and 108 are connected to a high voltage, such as the supply voltage V~c. Transistors 104 and 108 are always conductive and functi~n as resistors. A
transistor 112 has the drain terminal thereof connected to node 106 and the source terminal thereof connected to the latch node 46. The gate terminal of tr~nsistor 112 is connected to node 110. A transistor 114 has the drain terminal thereof connected to node 110, the source terminal thereof connected to node 46 and the gate terminal thereof connected to node ln6 ~ The sense`amplifier operation occurs after a memory cell has been connected to one of the bit lines, either ~20 30 or 38. One of the bit lines is then at a higher voltage than the other bit line. Assume, for example~
that bit llne 30 is at the higher voltage. When the . ~ latch signal~slowly~pulls node 4~ to ground, transistor ~; 114 will be turned on before transistor 112 because the gate to source bias on transistor 114 is greater han the gate to source bias on transistor 112. As transistor 114 is rendered conductive node 110 will be discha~rged through transistor 114 into the latch node 46. As node~ll0 is discharged the gate bias on transistor 30~ ;112~is 1owered~thus~preventing transistor 112 from being rendered conductive~ When the latch signal is pulled all the ~way to ground transistor 114 will continue ~to be conduc~ive since bit line 30 and node 106 remain at : , ' ~ ' : :
I .'~ l~9g~2 the previous high charge state. As node 110 is discharged, conduction through transistor 108 discharges bit line 38. Thus, after the latch signal has gone completely to ground bit line 38 will also be pulled S to ground.
If bit line 38 is at a higher voltage after a memory cell is connected to one of the bit lines, transistor 112 will be rendered conductive to discharge node 106 and pull bit line 30 to ground.
: 10 A schematic illustration for the pull-up circuits 60 and 68 is given in FIGURE 4. A transistor 120 has the drain terminal thereof connected to Vcc, the source terminal thereof connected to a node 122 and the :
gate terminal thereof connected to receive the precharge ~15 signal Pr A transistor 124 has the drain terminal thereof ; :connected to node I22, the source terminaI thereof connected to bit line 30 and:the gate terminal thereof connected to receive the precharge signal P0.
: : A transistor 126 has the drain terminal thereof 20 ~ connected~to receive the precharge signal Pl, the gate terminal thereof connected to node 122 and the source terminal thereof connected to the gate terminal of a~transistor:128. The drain terminal o transistor : 128~is c:onnecte~ to the trcc~and the source terminal 25~ thereof~:is connected to bit~line~30.
:When~the precharge~signal P is received trans:istor 20:îs:rendered conductive to precharge node 122 to a~high~oltag~state. Once~the:~precharge signal returns to a~:low:voltag~ level the~node 122 is left floating 30~ :at the~;high~voltage ~talte.~ When the precharge signal P~ goes to approximately 2 ~olts, transistor 124 is rendered~onductive if the~bit line 30 is at a ufficiently:low voltage state:such that there is at least one~;`transistor threshold voltage between the gate ; 3~5 ~and source terminals of transistor 124. If transistor : :`:: ~ :
~: ' ' ~' . ' `'` ' . . ,.
124 is rendered conductive node 12~ is discharged into the bit line 30.
But if the charge on bit line 30 is sufficiently high so that there is less than one transistor threshold voltage between the gate and source terminals of transistor 124, transistor 124 will not be rendered conductive by the precharge signal P0, leaving node 122 floating at a high voltage level. The Pl signal is then applied to the drain terminal of transistor 126. If node 122 is at a high voltage, transistor 126 is conductive so that the source of transistor 126 follows signal P1 - above Vcc. This is possible since the channel capacitance ~ of transistor 126 bootstraps node 122 to a hiyh voltage ; level. With the full voltage level of bootstr~pped precharge signal Pl applied to the gate ter~inal of transistor 128, the full supply voltage Vcc is applied to the bit line 3n, thereby pulling the bit line to the voltage state of Vcc. Thus when the voltage on the bit line 30 îs abov~ a preset level, the bit line will be elevated to the supply voltage by opera~ion of the precharge circuit 60, but if the vol~age on the bit line 30 is less than a preset level, the precharge circuit 60 will have~no effect upon the bit line 30.
In ~summary,~the present invention comprises a ~dynamic random~access memory in which bit lines are equilibrated to approximately one half of the supply vol~tage before a memory cell is connec~ed thereto. A
sense amplif~ier detects the voltage dif~erence on the bit lines caused by the connection of the storage ~capacitor to one of the bit lines and pulls the bit line having~a~lower voltage thereon to ground~ A
pull up circult elevates the bit line having the greater voltage thereon~ Af~er the voltage state is transferred ~hrough input~output lines and after the memory cell i5 isolated, the bit lines are permit~ed to float and are 1 ~ 699~
;' ~ ! ) connected together through a latch node so that the bit lines are returned to the equilîbration voltage as a result of charge transfer between the bit lines.
Although one embodiment of the invention has been illustrated in the accompanying drawings and described in the foregoing Detailed Description, it will be understood that the invention is not limited to the embodiment disclosed, but is capable of numerous rearrangements, modifications and substitutions without departiny from the scope of the invention.
: . :
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:
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:
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:
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'
Claims (9)
1. The method of operation for a dynamic random access memory, comprising the steps of:
storing a first voltage state or a second voltage state in a dynamic memory cell where said first voltage state corresponds to a first data state and said second voltage state corresponds to a second data state;
connecting said memory cell to one of a pair of bit lines, after said bit lines have been set to a third voltage state, to drive the bit line connected thereto to a fourth voltage state when said memory cell has had said first voltage state stored therein or to drive said bit line connected thereto to a fifth voltage state when said memory cell has had said second voltage state stored therein while the other bit line of said pair of bit lines substantially maintains said third voltage state thereon;
driving the one of said bit lines having the lower voltage thereon to a low voltage state after said memory cell has been connected to one of said bit lines;
driving the other of said bit lines to a high voltage state after said memory cell has been connected to one of said bit lines;
disconnecting said memory cell from the corresponding bit line after the corresponding bit line has been driven to either said low voltage state or to said high voltage state, and connecting together said bit lines of said pair after one of said bit lines has been driven to said low voltage state and the other of said bit lines has been driven to said high voltage state to equilibrate the voltages on said bit lines to said third voltage state where said third voltage state is between said first voltage state and said second voltage state and said third voltate state is also between said fourth voltage state and said fifth voltage state.
storing a first voltage state or a second voltage state in a dynamic memory cell where said first voltage state corresponds to a first data state and said second voltage state corresponds to a second data state;
connecting said memory cell to one of a pair of bit lines, after said bit lines have been set to a third voltage state, to drive the bit line connected thereto to a fourth voltage state when said memory cell has had said first voltage state stored therein or to drive said bit line connected thereto to a fifth voltage state when said memory cell has had said second voltage state stored therein while the other bit line of said pair of bit lines substantially maintains said third voltage state thereon;
driving the one of said bit lines having the lower voltage thereon to a low voltage state after said memory cell has been connected to one of said bit lines;
driving the other of said bit lines to a high voltage state after said memory cell has been connected to one of said bit lines;
disconnecting said memory cell from the corresponding bit line after the corresponding bit line has been driven to either said low voltage state or to said high voltage state, and connecting together said bit lines of said pair after one of said bit lines has been driven to said low voltage state and the other of said bit lines has been driven to said high voltage state to equilibrate the voltages on said bit lines to said third voltage state where said third voltage state is between said first voltage state and said second voltage state and said third voltate state is also between said fourth voltage state and said fifth voltage state.
2. The method recited in Claim 1 including the step of floating each of said bit lines after one of said bit lines has been driven to said low voltage state and the other of said bit lines has been driven to said high voltage state.
3. The method recited in Claim 2 wherein the step of connecting together said bit lines comprises connecting each of said bit lines to a common node.
4. The method recited in Claim 1 wherein the step of connecting together said bit lines comprises sharing charge between said bit lines such that said bit lines are equilibrated to said third voltage state and said third voltage state is approximately midway between said high voltage state and said low voltage state.
5. The method recited in Claim 1 wherein the step of driving the one of said bit lines having the lowest voltage thereon to a low voltage state occurs before the step of driving the other of said bit lines to a high voltage state.
6. A dynamic random access memory comprising:
at least one pair of bit lines, at least one dynamic memory cell for each of said bit lines wherein each memory cell has stored therein either a first voltage state which corresponds to a first data state or a second voltage which corresponds to a second data state, means for connecting one of said memory cells to the corresponding bit line in response to a memory address supplied to said memory and said bit lines have been floating at a third voltage state wherein the bit line connected to the memory cell is driven to a fourth voltage state if said memory cell connected thereto had said first voltage stored therein or said bit line is driven to a fifth voltage state if said memory cell connected thereto had said second voltage state stored therein, a sense amplifier connected to each of said bit line pairs for driving to a low voltage state the one of the bit lines connected thereto which has the lower voltage thereon when said sense amplifier receives a latch signal, a pull-up circuit for each of said bit lines for pulling the bit line connected thereto to a high voltage state after the other bit line of the pair has been driven to said low voltage state, means for disconnecting said memory cell from said bit line after the bit line previously connected thereto has been driven to either said low voltage state or said high voltage state, and means for connecting together the bit lines of said pair after one of said bit lines has been driven to said low voltage state and the other of said bit lines has been driven to said high voltage state to equilibrate the voltages on said bit lines at said third voltage state wherein said third voltage state is between said first voltage state and said second voltage state and said third voltage state is also between said fourth voltage state and said fifth voltage state.
at least one pair of bit lines, at least one dynamic memory cell for each of said bit lines wherein each memory cell has stored therein either a first voltage state which corresponds to a first data state or a second voltage which corresponds to a second data state, means for connecting one of said memory cells to the corresponding bit line in response to a memory address supplied to said memory and said bit lines have been floating at a third voltage state wherein the bit line connected to the memory cell is driven to a fourth voltage state if said memory cell connected thereto had said first voltage stored therein or said bit line is driven to a fifth voltage state if said memory cell connected thereto had said second voltage state stored therein, a sense amplifier connected to each of said bit line pairs for driving to a low voltage state the one of the bit lines connected thereto which has the lower voltage thereon when said sense amplifier receives a latch signal, a pull-up circuit for each of said bit lines for pulling the bit line connected thereto to a high voltage state after the other bit line of the pair has been driven to said low voltage state, means for disconnecting said memory cell from said bit line after the bit line previously connected thereto has been driven to either said low voltage state or said high voltage state, and means for connecting together the bit lines of said pair after one of said bit lines has been driven to said low voltage state and the other of said bit lines has been driven to said high voltage state to equilibrate the voltages on said bit lines at said third voltage state wherein said third voltage state is between said first voltage state and said second voltage state and said third voltage state is also between said fourth voltage state and said fifth voltage state.
7. The dynamic random access memory recited in Claim 6 including means for isolating each of said bit lines after one of said bit lines has been driven to said low voltage state and the other of said bit lines has been driven to said high voltage state.
8. The dynamic random access memory recited in Claim 6 wherein said means for connecting together the bit lines comprises a first transistor having the drain and source terminals thereof connected between one of said bit lines of said pair and a latch node of said sense amplifier and a second transistor having the drain and source terminals thereof connected between the other bit line of said pair and said latch node, the gate terminals of said transistors connected to receive an equilibrate signal which renders said transistors conductive and equilibrates the voltage on said bit lines to said third voltage by charge transfer between said bit lines.
9. The dynamic random access memory recited in Claim 6 wherein each of said memory cells comprises an access transistor having the drain terminal thereof connected to one of said bit lines, and the gate terminal thereof connected to a row line and the source terminal thereof connected to a first terminal of a storage capacitor having a second terminal thereof connected to a common node.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| PCT/US1980/000673 WO1981003568A1 (en) | 1980-06-02 | 1980-06-02 | Dynamic random access memory |
| US80/00673 | 1980-06-02 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1169962A true CA1169962A (en) | 1984-06-26 |
Family
ID=22154381
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000378895A Expired CA1169962A (en) | 1980-06-02 | 1981-06-02 | Dynamic random access memory |
Country Status (4)
| Country | Link |
|---|---|
| EP (1) | EP0054022A4 (en) |
| JP (1) | JPH0449194B2 (en) |
| CA (1) | CA1169962A (en) |
| WO (1) | WO1981003568A1 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20110208886A1 (en) * | 2010-02-24 | 2011-08-25 | Denso Corporation | Communication slave |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS59203298A (en) * | 1983-05-04 | 1984-11-17 | Nec Corp | Semiconductor memory |
| JPS62150587A (en) * | 1985-12-24 | 1987-07-04 | Matsushita Electric Ind Co Ltd | Active restore circuit |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US4004284A (en) * | 1975-03-05 | 1977-01-18 | Teletype Corporation | Binary voltage-differential sensing circuits, and sense/refresh amplifier circuits for random-access memories |
| DE2634089B2 (en) * | 1975-08-11 | 1978-01-05 | CIRCUIT ARRANGEMENT FOR DETECTING WEAK SIGNALS | |
| JPS5922316B2 (en) * | 1976-02-24 | 1984-05-25 | 株式会社東芝 | dynamic memory device |
| JPS5352022A (en) * | 1976-10-22 | 1978-05-12 | Hitachi Ltd | Pre-amplifier |
| US4107556A (en) * | 1977-05-12 | 1978-08-15 | Rca Corporation | Sense circuit employing complementary field effect transistors |
| US4162416A (en) * | 1978-01-16 | 1979-07-24 | Bell Telephone Laboratories, Incorporated | Dynamic sense-refresh detector amplifier |
| JPS54100233A (en) * | 1978-01-24 | 1979-08-07 | Nec Corp | Integrated memory |
| JPS54101228A (en) * | 1978-01-26 | 1979-08-09 | Nec Corp | Mos memory circuit |
-
1980
- 1980-06-02 EP EP19800901815 patent/EP0054022A4/en not_active Withdrawn
- 1980-06-02 JP JP50211580A patent/JPH0449194B2/ja not_active Expired
- 1980-06-02 WO PCT/US1980/000673 patent/WO1981003568A1/en not_active Application Discontinuation
-
1981
- 1981-06-02 CA CA000378895A patent/CA1169962A/en not_active Expired
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US20110208886A1 (en) * | 2010-02-24 | 2011-08-25 | Denso Corporation | Communication slave |
| US8762612B2 (en) * | 2010-02-24 | 2014-06-24 | Denso Corporation | Communication slave |
Also Published As
| Publication number | Publication date |
|---|---|
| JPH0449194B2 (en) | 1992-08-10 |
| WO1981003568A1 (en) | 1981-12-10 |
| JPS57501001A (en) | 1982-06-03 |
| EP0054022A1 (en) | 1982-06-23 |
| EP0054022A4 (en) | 1984-11-05 |
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