CA1179060A - Semiconductor memory device - Google Patents
Semiconductor memory deviceInfo
- Publication number
- CA1179060A CA1179060A CA000398528A CA398528A CA1179060A CA 1179060 A CA1179060 A CA 1179060A CA 000398528 A CA000398528 A CA 000398528A CA 398528 A CA398528 A CA 398528A CA 1179060 A CA1179060 A CA 1179060A
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- CA
- Canada
- Prior art keywords
- bit lines
- extra
- data
- bit
- memory cells
- 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.)
- Expired
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Classifications
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F11/00—Error detection; Error correction; Monitoring
- G06F11/07—Responding to the occurrence of a fault, e.g. fault tolerance
- G06F11/08—Error detection or correction by redundancy in data representation, e.g. by using checking codes
- G06F11/10—Adding special bits or symbols to the coded information, e.g. parity check, casting out 9's or 11's
- G06F11/1008—Adding special bits or symbols to the coded information, e.g. parity check, casting out 9's or 11's in individual solid state devices
-
- G—PHYSICS
- G06—COMPUTING; CALCULATING OR COUNTING
- G06F—ELECTRIC DIGITAL DATA PROCESSING
- G06F11/00—Error detection; Error correction; Monitoring
- G06F11/07—Responding to the occurrence of a fault, e.g. fault tolerance
- G06F11/08—Error detection or correction by redundancy in data representation, e.g. by using checking codes
- G06F11/10—Adding special bits or symbols to the coded information, e.g. parity check, casting out 9's or 11's
- G06F11/1076—Parity data used in redundant arrays of independent storages, e.g. in RAID systems
Abstract
Abstract of the Disclosure A semiconductor memory device comprises at last one word line, a plurality of bit lines extending across the word line, a data memory cell unit including a plurality of data memory cells connected between the word line and the bit lines for storing information, a plurality of first extra bit lines corresponding to first gorups of the bit lines, each of which has k bit lines (k is an integer), and extending across the word line, a plurality of first extra memory cells connected between the word line and the first extra bit lines for storing first checking information with respect to the first gorups of the bit lines, a plurality of second extra bit lines corres-ponding to second groups of the bit lines, each of which group has m bit lines (m is an integer), and extending across the word line, a plurality of second extra memory cells connected between the word line and the second extra bit lines for 5 storing second checking information with respect to the second groups of the bit lines, an error detection circuit for comparing the information fed from the data memory cells with the contents of the first and second extra memory cells to' detect errors, and a ciruit responsive to an output from the error detection circuit for correcting the information fed from the data memory cells, the first extra bit lines being grouped correspondingly to the first groups of the bit lines, the second extra bit lines being goruped correspondingly to the second groups of the bit lines, each of the second groups of the second extra bit lines being composed of the of the first extra bit lines in each first group thereof.
Description
Specification Title of the Invention Semiconductor Memory Device Background of the Invention The present invention relates to a semiconductor memory device, and more particularly to a semiconductor memory device for storing data containing a function of correcting the error of at least one bit.
Some prior semiconductor memory devices lnclude auxiliary saving bit lines which serve to replace fixed defective bit lines produced at manufacturing stages for thereby improving the yield of memory dev1ces. The replacement of defective bits with rescue bits in such semiconductor memory devices is carried out by a circuit designed exclusively for the replacing operation, a laser device, or other suitable devices. With the conventional arrangement, while the fixed defective bits included during the fabrication steps can be remedied, no unfixed bit defects which could b~ created by the encounter with alpha rays or the like can be saved at all.
There have been developed various systems for correcting bit errors on LSI chips which contain semiconductor memory devices, utilizing the following techniques:
(1) Error correction on majority logic;
Some prior semiconductor memory devices lnclude auxiliary saving bit lines which serve to replace fixed defective bit lines produced at manufacturing stages for thereby improving the yield of memory dev1ces. The replacement of defective bits with rescue bits in such semiconductor memory devices is carried out by a circuit designed exclusively for the replacing operation, a laser device, or other suitable devices. With the conventional arrangement, while the fixed defective bits included during the fabrication steps can be remedied, no unfixed bit defects which could b~ created by the encounter with alpha rays or the like can be saved at all.
There have been developed various systems for correcting bit errors on LSI chips which contain semiconductor memory devices, utilizing the following techniques:
(1) Error correction on majority logic;
(2) On-chip encoding/decoding circuit using an error correcting code; and
(3) On-chip horizontal and vertical parity check system.
The technique (1~ however requires a chip having an area which is about three times as large as the area of a chip with no error correction arrangement thereon. The expedient (2) necessitates an additional error correation circuit which is of a relatively large scale and will consume an increased amount of electric power. The system (3) needs a large number of check bits because of parity checking required on a'l of data bits for correcting the error of one bit, and hence takes an extended period of time for error correction and results in increased electric power consumption.
Summary of the Invention It is a primary object of the present invention to provide a semiconductor memory device containing therein fewer bit errors than conventional semiconductor memory devices for improved effective yield at the time of fabrication or higher reliab-ility in operation.
Another object of the present invention is to provide a semiconductor memory device which is compact in size.
Still another object of the present invention is to provide a semiconductor memory device which will not consume an increased amount of electric power despite its ability to reduce bit errors.
A still further object of the present invention is to provide a semiconductor memory device which includes an additional small-scale circuit that is self-corrective of bit ~t7~0~0 errors within a short period of time.
To achieve the foregoing objects, a semiconductor memory device according to the present invention incorporates therein a one-dimensional horizontal and vertical parity checking system.
As is well known, a horizontal and vertical parity checking system uses additional horizontal and vertical parity bits of logic "1" or "0" in rows and columns of a plurality of information data bits on an MxN matrix such that the total number of ls (or Os) in each row and column plus the parity bit is always an even or odd number. If an error occurs in any data bit, the position of such erroneous data bit can be located by checking all of horizontal and vertical parity bit information. The known horizontal and vertical parity checking system is two-dimensional.
According to the present invention, there is provided a semiconductor memory device comprising at least one word line, a plurality of bit lines extending across the word line, a data memory cell unit including a plurality of data memory cells connected between the word line and the bit lines for storing information, a plurality of first extra bit lines corresponding to first groups of the bit lines, each of which group has k bit lines (k is an integer), and extending across the word line, a plurality of first extra memory cells connected between the word line and the first extra bit lines for storing first checking information with respect to the s30~
first groups of the bit lines, a plurality of second extra bit lines corresponding to second groups of the bit lines, each of which group has m bit lines (m is an integer), and extending across the word line, a plurality of second extra memory cells connected between the word line and the second extra bit lines for storing second checking information with respect to the second groups of the bit lines, an error detection circuit for comparing the information fed from the data memory cells with the contents of the first and second extra memory cells to detect errors, and a circuit responsive to an output from the error detection circuit for correcting the information fed from the data memory cells, the first extra bit lines being grouped correspondingly to the first groups of the bit lines, the sec~nd extra bit lines being grouped correspondingly to the second groups of the bit lines, each of the second groups of the second extra bit lines being composed of one of the first extra bit lines in each first group thereof.
The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying ~rawings in which certain preferred embodiments of the invention are shown by way of illustrative example.
Brief Description of the Drawings Figs. lA and lB are diagrammatic views showing the principles of horizontal and vertical parity checking systems applicable to a semiconductor memory device according to the 1~7~0~V
present invention;
Fig~ 2 is a block diagram illustrative of the fundamental arrangement of a semiconductor memory device constructed on the principles shown in Figs. lA and lB;
Fig. 2A is an enlarged circuit diagram of a data memory cell in the semiconductor memory device shown in Fig. 2;
Fig. 3 is a circuit diagram of a parity checking circuit in the semiconductor memory device illustrated in Fig.
2;
Fig. 4 is a circuit diagram of a parity bit generator in the semiconductor memory device; and Fig. 5 is a block diagram of a semiconductor memory device according to another embodiment of the present invention.
Detailed Description of the Preferred Embodiments Fig. lA shows horizontal parity bits a and vertical parity bits b which are appended horizontally and vertically respectively to a 4x4 matrix of 16 data bits. The parity checking system shown in Fig. lA is an even-parity-bit checking system in which the sum of l-bits in each horizontal row and vertical column is always even. For the sake of brevity, the even-parity-bit checking system will be relied on throughout the specification.
By transferring the data bits and the parity check bits a, b along the dotted-line arrows in Fig. lA, the two-dimensional matrix can be transformed into a one-di~ensional matrix as illustrated in Fig. lB. Any errors in upper 16 data ~t79060 bits out of the total of 24 bits in the one-dimensional matrix can detected in position by comparing groups of bits connected by solid lines with lower 8 parity bits. ThuS, a fixed or unfixed bit defect in any one of the upper 16 bits can be detected and corrected with ease. The foregoing arrangement is - indicative of the principle of the present invention based on which a sing~e erroneous bit can be corrected.
Fig. 2 illustrates a semiconductor memory device according to an embodiment of the present invention. The semi-conductor memory device includes a data memory cell unit 100for storing data bit information which comprises a matrix of data memory cells 10011 each including, as shown in Fig. 2A, a field-effect transistor 102 and a capacitor 103 connected in series between a bit line and the ground, the transistor 102 having a gate connected to a word line. The construction and operation of the data memory cells are well known in the art and hence will not be described in detail. The semiconductor memory device also has a parity cell unit 120 for storing horizontal and vertical parity check bit information. The parity cell unit 120 is composed of a first excess memory cell matrix 120h for storing horizontal parity check bit information, and a second excess memory cell matrix 120V for storing vertical parity check bit information. Each of the matrices 120h, 120V have a plurality of memory cells each of which is of the same construction as that of the data memory cell described above. A parity checking and correcting unit 6(~
130 comprises horizontal parity checking circuits 130hl-130hm, vertical parity checkin~ circuits 130V1-130Vk, a one-bit error correction circuit 132, and a data output circuit 134.
Each of the parity checking circuits 130hl-130hm, 130Vl-130Vm in the parity checking and correcting unit 130 is, for example, constructed as shown in Fig. 3. In this example, k (orm) is defined as 8 and each parity checking circuit is composed of eight EXCLUSIVE-OR gates 201-208. Each of the gates 201-204 is supplied with two bits out of eight data bits indicated at j. The gate 205 is supplied with outputs from the gates 201, 202, and the gate 206 is supplied with outputs from the gates 203, 204. The gates 205, 206 produce outputs that are fed to the gate 207. The gate 208 is supplied with an output from the gate 207 and a signal indica-tive of a parity check bit p. The gate 208 produces an output, which is delivered as an output from each parity checking circuit. The 8-bit data bit information j is supplied from the output of the data memory cell unit 100, that is, data bit lines corresponding to selected memory cells. Thus, the parity checking circuit 130hl receives data bit information from data bit lines 16011, 16021, ... 160kl, and a parity check bit p from a bit line 120hl in the first excess memory matrix 120h. The other parity checking cirucits 130h2-130hm are supplied with data bits and parity check bits over corresponding bit lines. The parity checking circuits 130Vl-~'79 ~ ~ ~
! 130Vk are supplied with data bi~s from the same data bit , lines, and with parity check bits p respectively fxom bit lines ¦ in the second excess memory cell matrix 120V.
As shown in Fig. 2, the one-bit error correction circuit 132 comprises AND gate 220ll-220k1, 12 k2~ 2201k-220km, and EXCLUSIVE-IR gates 3011-230kl~ 23012-230k2, 2301m 230km gate 220ll performs logical multiplication on, or ANDing of, an output from the horizontal parity checking circuit 130 and an output from the vertical parity checking circuit 130Vl. If the result of such logical multiplication is "O", it means that the contents of the data memory cells agree with those of the related horizontal and vertical parity check bits. Conversely, if the logical multiplication results is "1", it means that the contents of the data memory cells don1t agree with those of the related horizontal and vertical parity ¦ check bits. The AND gate 2201l delivers its output to the EXCLUSIVE-OR gate 23011. When the output of the AND gate 1 220ll is ~iO", the EXCLUSIVE-OR gate 2301l allows an output 2~ from the data memory cell unit lOO over the data bit line 160ll to pass therethrough as its own output. When the output of the AND gate 220ll is "l", the EXCLUSIVE-OR gate 230ll reverses an output from the data memory cell unit 100 over the data bit line 160ll, that is, corrects a one-bit error, and delivers such a reversed output to a subsequent stage. The other AND gates 22021-220km and associated ~7~
EXCLUSIVE-O~ ~ates 23021-230km operate in the same manner.
The data output circuit 134 serves to issue succes-si~-ely outputs or corrected data from the one-bit error correction circuit 132 based on bit selection signals.
The semiconductor memory de~ice also includes a data input circuit 140 for delivering data supplied from an outside processing circuit (not shown) only to selected memory cells in the data memory cell unit 100 based on bit selection signals BSl. The other unselected memory cells in the data memory cell unit 100 supplied by the data input circuit 140 with outputs from the one-bit error correction circuit 132. The data input circuit 140 has switch or gate circuits 140A
responsive to the bit selection signals BSl for selectively delivering the data ~rom the outside processing circuit and the bit information from the correction circuit 132 to the bit lines connected to the data memory cell unit 100. When the bit lines for memory cells in which new data are to be written are designated by the bit selection signals, the data input circuit 140 delivers exterior data to such selected bit lines and data from the correction circuit 132 to the other bit lines that are not selected. The semiconductor memory device includes word lines l50i-150in. The data bit lines 16011-160kl, 12 60k2, ... 1601m-160km jointly constitute lxm lines. The horizontal parity check bits are generated by over the data bit lines in groups of k bits, and hence the data bit lines are divided into m groups each for delivering k bits.
~'79(~6{3 The total number of the horizontal and vertical parity bit lines is k+m. The horizontal parity bit lines are divided into groups corresponding respectively to the data bit lines grouped 11 kl~ 16012-160k2, ... 1601m-160k , and the vertical parity bit lines are ~rouped into divisions corresponding respectively to the data bit lines grouped as 11' 1612 ~ 1601m, 16021, 16022 ... 160 160kl, 16k2 ' 160km -~orizontal parity check bit generators 170hl~170hm are provided respectively for the foregoing groups of horizon-tàl parity check bit lines, and vertical parity check bit generators 170Vl-170Vk are provided respectively for the above groups of vertical parity check bit lines.
The (kxm) data bit lines which are connected to the outputs of the data input circuit 140 and are divided into m groups each for k bits for forming horizontal parity bit information in k bits, are coupled to the horizontal parity check bit generators 170hl-170hm which are m in number.
The (kxmj data bit lines which are divided into k groups each for m bits for forming vertical parity bit information in m bits, are coupled to the vertical parity ch~ck bit senerators 170Vl-170Vk which are k in number.
As shown in Fig. 4, in the case of k (or m) = 8, each of the parity check bit generators 170hl~170hmr 170Vl-170Vk comprises seven EXCLUSIVE-OR gates 241-247 which are connected in the same arrangement as that of the ~'7~3~6~
EXCLUSIVE-OR gates 201-207 as enclosed by the dotted line in each parity checking circuit illustrated in Fig. 3. The EXCLUSIVE-O~ gates 241-244 are supplied with the inputs j which are fed also to the EXCLUSIVE-OR gates 201-204. The first excess memory cell matrix 120h in the parity cell unit 120 for storing the horizontal parity check bit information includes m excess bit lines corresponding respectively to the m groups of data bit lines for creating the h~orizontal parity check bit information. The second excess memory cell matrix 120V for storing the vertical parity bit check information includes k excess bit lines corresponding respectively to the k groups of data bit lines for forming the vertical parity check bit information. These excess bit lines are coupled to the word lines 150il-150in by excess memory cells in the first and second memory cell matrices 120h, 120V of the parity cell unit 120.
When any one of the word lines 150il-150i~ is energized, data bit information of (kxm~ bits is read out of the data memory cells which are connected ~o the activated word line and led as m groups of data bit information each in k bits, correspondiny to the grups o (kxm) data bit lines, to the m horizontal parity checking circuits 130hl-130hm, respectively. The (kxm)-bit data information as divided in k groups each in m bits is delivered as grouped to the vertical pàrity checking circuits 130Vl-130Vk. The m-bit horizontal parity check bit information and the k-bit vertical parity ~t7~0 check bit information, which are read simultaneously with the reading of the (kxm)-bit data information, are supplied as checking information to the parity checking circuits 130hl-130hm, 130Vl-130Vk for the corresponding groups.
Output signals from the horizontal parity checking circits 130hl-130hm and those from the vertical parity checking circuits 130Vl-130Vk are delivered as inputs respectively to the AND gates 22011-220km of the correction circuit 132 to detect whether there is no error horizontally and vertically in the data bit information read from the data memory cell unit 100. The AND gates 22011-220km are (kxm) in number and divided into groups each containing k gates. Each of the AND
gates, grouped as 22011-220kl, 22012-220k2, .--2201m-220km is supplied at one of its inputs with an output signal from one of the horizontal parity checking circuits 130hl-130hm, and is also supplied at the other input with an output from one of the vertical parity checking circuits 130Vl-130Vk. This arrangement determines whether there is no error in each delivered piece of data bi-t information horizontally and vertically. With the even-parity-bit checking system employed, the horizontal parity checking circuits 130hl-130hm will produce an output signal of "1" where an error is detected upon horizontal checking, and the vertical parity checking ~ircuits 130~1-130Vk will generate an output signal of "l" where an error is detected upon vertical checking.
~7~
The (kxm) AND gates 22011-220km deliver their output signals to the (kxm) EXCLUSI~E-OR gates 23011-230km, respectively. The EXCLUSIVE-OR gates 23011-230km will reverse the logical values of the data bit information fed from the data memory cell unit 100 only when such supplied data bit information contains an error in both the horizontal and vertical directions. The output signals from the EXCLUSIVE-OR
gates 23011-230km go to the output circuit 134 and simul-taneously to the input circuit 140 as error-corrected data bit in~ormation by way of feedback paths 180.
Data information operation of the circuit arrangement shown in Fig. 2 will be described. When a desired one of the word lines 150il-150in is activated, (kxm)-bit data bit information is read in parallel from a corresponding one of the groups of data memory cells in the data memory cell unit 100, which are connected to the selected word line, and at the same time, parallel m-bit horizontal parity check bit information and parallel k-bit vertical parity check bit information are read from the excess memory cells in the excess memory cell matrices 120h, 120V, which are connected to the selected word line. The (kxm)-bit data bit information thus read from the memory cell unit 100 is supplied one bit at a time to the EXCLUSIVE-OR gates 23011-230km in the error correction circuit 132, and is also supplied as grouped to the horizontal and vertical parity checking circuits 130hl-130hm, 130Vl-130Vk. The horizontal parity checking circuits 130hl-130hm compare the supplied data bit information with the horizontal pari~y check bit information read from the memory cell matrix 120h to determine whether there is an error horizontàlly/ and produce signals of "1" indicative o~
such an error when the error is included. Likewise, the vertical parity checking circuits 130Vl-130Vk compares the supplied data bit information with the vertical-parity check bit information read from the memory cell matrix 120V to determine whether an error is included verticaly, and generate signals of "1" indicative of such an error when the error takes place. The output signals from the horizontal parity checking circuits 130hl-130hm and the vertical parity checking circuits 130Vl-130Vk are delivered to the error correction circuit 132.
An instance in which the data bit information supplied to the EXCLUSIVE-OR gate 23011 contains an error will be described. The output signals from the horizontaL parity checking circuit 130hl and the vertical parity checking circuit 130Vl are "1". The logical value of only the data bit information fed to the EXCLUSIVE-OR gate 230l1 is reversedt whereas the other data bit information is supplied as it is to the output circuit 134. The correction circuit 132 produces as outputs error-corrected data bit information. The error-corrected data bit information is delivered as an output by the output circuit 134 with desired one or more bits selected by ~he bit selection signal BS2. At the same time, the output signals from the error correction circuit 132 are fed back via feedback lines 180 to the input circuit 140, ~rom which the signals are stored again in the original memory cell positions in the data memory cell unit 100. Upon storing again such signals, horizontal and vertical parity check bit information based on the error-corrected data bit information is written in corresponding extra memory cells in the first and second extra memory cell matrices 120h, 120V.
New data bit information supplied from the exterior source will be written in as follows: The bit selection signal BSl is supplied to the input circuit 140 to indicate in which data memory cell on a desired word line new data should be written. The word line to which is connected the data memory cell in which the new data is to be written is energized at first, for thereby reading all of the data bit information from the data memory cells coupled to that word line in a manner similar to that for the foregoing data reading operation.
Then, data bit information fed back from the error correction circuit 132 is caused to be stored again in the other data memory cells than the data memory cell in which the new data should be stored. Simultaneously, the data bit information from the exterior source is stored in the desired data memory cell. At this time, horizontal and vertical parity check bit information based on the new data bit information from the exterior source and the data bit information fed back from the error correction circuit 132 is formed in the parity check bit ~7~ O~ ~
170hl 170hm' 170vl~l70vk/ and stored in the extra memory cell matrices 120h, 120V.
The semiconductor memory device thus constructed has the following advantages:
~1) Horizontal and vertical parity checking can be performed at one time within the memory by activating a word line, that is, one-dimensional parity checking can be carried out. Bit errors produced in the memory device are thus fewer than those experienced with conventional memory devices, with the result that the effective yield of semiconductor memory devices can be increased or the semiconductor memory devices will operate with improved reliability. For example, assuming that the yield is expressed by the probability that the number of defective bits per word line with respect to the rate of occurence complete non-defective memory devices is 1 or less, the yields of conventional memory devices with no error correction circuits are 1~, 5%, and 10%, whereas corresponding yields of memory devices of the present invention are 25~, 41~, and 50% respectively. Therefore, the yields of semiconductor memory devices according to the present invention are much higher than the pr~ior yields, and are substantially e~ual to those of peripheral circuits for memory devices, which can be manufactured on the current semiconductor fabrication technol-ogy. The rate of increase of reliability of the semiconductor memory device will be described with reference to soft errors caused by alpha rays. The rate of occurence of a soft error in 1~79(~
an LSI memory device with 1 Mb having no error correction circuit can be determined by the probability that one alpha-ray particle hits a single memory cell. With the present invention, the same rate can be determined by the probability that one alpha-ray particle impinges upon two or more memory cells within an error correction period. For a 1 Mb RAM as an example, a rate of occurence of a soft error in a conven-tional semiconductor memory device is 103 FIT (FIT=10 9/
hour) whereas a corresponding error occurence rate in a semi-conductor memory device of the present invention is 10 FIT, and another prior error occurence rate is 106 FIT while a corresponding error occurence rate according to the present invention is 10 2 FIT. The rate of occurence of soft errors in the semiconductor memory device of the invention is therefore quite reduced.
(2) With the arrangement of the present invention, most of an additional circuit required for correcting bit errors is in the parity cell unit, and the number of gates required in the parity checking and correcting unit is on the order of 4000 for a 1 Mb RAM. The ratio of the ~parity cell unit to the memory cell unit is 2 J~where N2 is the memory capacity, and hence becomes smaller as the memory capacity grows larger. The time interval ta required for error correction is given by:
ta = (3 + log2 ~) x ~ t where N is the square root of the memory capacity (N2=memory l~t7~
eapacity), and Q t is the delay time per gate. The error correction time for a 1 Mb RAM with ~ t=2 ns is 16 ns. with the added error correction circuit being small in scale according to the present invention, an increase in electric power consumption due to the added eircuit is expeeted to amount to lO mW or less for a 1 Mb RAM. Such a small inerease in the consumed electric power-does not substantially impair the memory performance. The semieonductor memory device aceording to the present invention is therefore advantageous in that the memory deviee itself ean be compact in size, is eapable of eorreeting bit errors within a short period of time, and does not involve a large increase in electric power eonsumption.
The semieonductor memory deviee aecording to the foregoing embodiment fails to correct two or more bit errors in one group out of the horizontal m bit line groups, or two or more bit errors in one group out of the vertical k bit line groups. ~owever, the semiconductor memory device can have a function of correcting two or more bit errors by causing code information eapable of detecting two or more bit errors, instead of parity eheek bit information, to be stored in the extra memory cell matrices 120h, 120V.
Fig. 5 shows a semiconductor memory device according to another embodiment of the present invention, particularly a semiconductor memory device of plural words x 1 bit type.
Identical or corresponding parts in Fig. 5 are denoted by 9(~0 identical or corresponding re~erence characters in Fig. 2. A
data memory cell matrix or unit 100 and a parity cell 120 composed of first and second extra memory matrices 120h, 120V are of the same construction of those illustrated in Fig. 2. Therefore, the data memory cell unit 100 comprises a (kxm)-bit matrix arranged one-dimensionally in a pattern as shown in Fig. lB, with memory cells being connected to common word lines. There are m groups of bit lines 16011-160kl, 12 6k2' 1601m- 160km, and each group consisting of k bits.
Selectors 3001 300m are provided respectively for the m groups of data memory cells in the data memory cell unit 100. Now, suppose that several upper bits or several lower bits within bits of the external address signal are used as an address signal Sl and the remaining bits as an address signal S2. Each selector is connected to the bit lines in a corres-ponding group of data memory cells, and serves to select one-bit data bit in~ormation from k-bit data bit information in response to the signal Sl. Where information i.n a memory celll for example, information stored in the memory cell connected to the bit line 16011 and the word line 150il is read out, the address signal Sl is supplied to the selectors 3001r 32 ... 300m to select the uppermost bit line 11' 6012, 16013 ... 1601m of each o~ the in bit groups, each of which is constituted by k bit lines. As an example, the bit line 16011 is connected to the output of the 7'3~
selector 3001, the bit line 16012 is connected to the output of the selector 32~ and the bit line 1601m is connected to the output of the selector 300m. Selected information of the memory cells connected to-these bit lines and the word line 150il is outputted to the vertical parity check circuit 310. Selected output signals from the selectors are supplied as data bit information for verticl parity checking to a vertical parity checking circuit 310. The vertical parity checking circuit 310 is composed of a plurality of EXCLUSIVE-OR gates as with the above embodiment of Fig. 2, and is receptive of, besides the outputs from the selectors, a corresponding output from a vertical parity cell matrix 120V
via a vertical parity check bit generator 420 described in detail later on. The vertical parity checking circuit 310 produces an output as a result of vertical parity checking.
A selector 320 serves to select grouped k-bit data bit inforamtion from the (kxm)-bit data bit information supplied from the data memory cell unit 100 in response to an address signal S2. That is, the address signal S2 i-s supplied to the selector 320 to select k bit lines 16011, 16021, 160kl, each of which constitutes the uppermost bit line group. Selected information of the memory cells connected to these bit ~ines and the word line 150il is outputted to the horizontal parity check circuit 340 from the selector 320.
Data bit information from a selected group of bit lines is delivered as an output from the selector 320 to a selector 330 ~ ~'79 ~ ~ ~
and to a horizontal parity checking circuit 340 as data bit information for hori~ontal parity checkingO The horizontal parity checking circuit 340 is composed of a plurality of ~ .
EXCLUSIVE-OR gates as with the corresponding circuit of the foregoing embodiment. The horizontal parity checking cirucit 340 also receives an output from a horizontal parity cell matrix 120h via a horizontl parity check bit generator 410, and produces an output as a result of horizontal parity checking.
The selector 330 is in response to an address signal Sl for selecting data bit information fed from the groups of bit lines.
Outputs from the parity checking circuits 310, 340 and an output from the selector 330 are supplied to a one-bit error correction circuit 350. The error correction circuit 340 comprises an AND gate 352 receptive of the output from the horizontal parity checking circuit 340 and the output from the vertical parity checking circuit 310, and an EXCLU~IVE-OR gate 354 receptive of an output from the AND gate 352 and an output from the selector 330. The error correction circuit 350 serves to reverse the output from the selector 330 when both of the outputs from the parity checking circuits 340, 310 are "1" r and issues such a reversed output. The output from the error correction circuit 350 is delivered out of the memory devicea The output from the error correction circuit 350, that is, error-corrected data bit information is fed back to the input of the error correction circuit 350 via a feedback path 370. The error-corrected data bit information thus fed back is stored again into desired memory cells or storage positions in the data memory cell unit 100 through the selectors 330, 320.
When it is necessary to write new input data in rela-. . .
tion to t~e above re-storlng operation, such new lnput data is supplied via a switch 401 in a data input circuit 400 to the output of the selector 330 and then stored via the selectors 330, 320 into desired memory cells in the data memory cell unit 100. Simultaneously with the writing of the new data in the data memor~ cell unit 100, the following parity data generating operation is performed.
The input circuit 400 includes an EXCLUSIVE-OR gate 403 in addition to the switch 401. The EXCLUSIVB-OR gate 403 is receptive of new input data and the output from the one-bit error correction circuit 350 to determine whether the new write data from the exterior source is different from the previous data. If different, then the EXCLUSIVE-OR gate 403 delivers an output, and horizontal and vertical parity check bit informa-tion related to the new data is supplied to horizontal and vertical parity check bit generators 410, 420.
The horizontal parity check bit gener-ator 410 comprises an EXC~USIVE-OR gate 411, a gate or switch 413, and a selector 415. The EXCLUSIVE-OR gate 411 is supplied with an output from the gate 403 in the data input circuit 400 and an output from the selector 415. when the gate 413 receives the control signal CSl, an output of the gate 411 is stored via the selector 415 into a corresponding memory cell in the first l'~t7~
extra memory matrix 120h as horizontal parity check bit information. The gate 411 issues an output of "1" only when the inputs thereto are different from each other.
.. . . . . .
- ~ ~ The vertical parity check bit generator -~2a comprises an EXCLUSIVE-OR ~ate 421, a gate or switch 423, and a selector 425. the EXCLUSIVE-OR gate 421 is supplied with an output from the gate 403 in the data input circuit 400 and an output from the selector 415. When the control signal CSl is fed to the gate 423, an output of the gate 41 is stored as vertical parity check bit information ito a corresponding memory cell in the second extra memory cell matrix 120V via the selector 425.
The gate 421 produces an output of "1" only when the inputs thereto are different from each other.
With the arrangement according to the embodiment shown in Fig. 5, both fixed and unfixed bit errors can be saved or corrected. Particularly, the semiconductor memory device illus~rated in Fig. 5 includes selectors for selecting data bit information necessary ~or generating horizontal and vertical parity check bit information and for horizontal and vertical parity checking, such that the wiring area and peripheral circuits needed can be smaller than that in the semiconductor memory device of Fig. 2. For example, the number of the gates constituting the parity checking/correctng unit becomes about one thirty-second (32th) of that of the embodiment shown in Fig. 2 that is about 140 gates. As described aboe, the semiconductor memory devices according to the present invention ~7~0~0 are advantageous in that they can save or correct both Eixed and unfixed bit errors.
Although certain preferred embodiments have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.
The technique (1~ however requires a chip having an area which is about three times as large as the area of a chip with no error correction arrangement thereon. The expedient (2) necessitates an additional error correation circuit which is of a relatively large scale and will consume an increased amount of electric power. The system (3) needs a large number of check bits because of parity checking required on a'l of data bits for correcting the error of one bit, and hence takes an extended period of time for error correction and results in increased electric power consumption.
Summary of the Invention It is a primary object of the present invention to provide a semiconductor memory device containing therein fewer bit errors than conventional semiconductor memory devices for improved effective yield at the time of fabrication or higher reliab-ility in operation.
Another object of the present invention is to provide a semiconductor memory device which is compact in size.
Still another object of the present invention is to provide a semiconductor memory device which will not consume an increased amount of electric power despite its ability to reduce bit errors.
A still further object of the present invention is to provide a semiconductor memory device which includes an additional small-scale circuit that is self-corrective of bit ~t7~0~0 errors within a short period of time.
To achieve the foregoing objects, a semiconductor memory device according to the present invention incorporates therein a one-dimensional horizontal and vertical parity checking system.
As is well known, a horizontal and vertical parity checking system uses additional horizontal and vertical parity bits of logic "1" or "0" in rows and columns of a plurality of information data bits on an MxN matrix such that the total number of ls (or Os) in each row and column plus the parity bit is always an even or odd number. If an error occurs in any data bit, the position of such erroneous data bit can be located by checking all of horizontal and vertical parity bit information. The known horizontal and vertical parity checking system is two-dimensional.
According to the present invention, there is provided a semiconductor memory device comprising at least one word line, a plurality of bit lines extending across the word line, a data memory cell unit including a plurality of data memory cells connected between the word line and the bit lines for storing information, a plurality of first extra bit lines corresponding to first groups of the bit lines, each of which group has k bit lines (k is an integer), and extending across the word line, a plurality of first extra memory cells connected between the word line and the first extra bit lines for storing first checking information with respect to the s30~
first groups of the bit lines, a plurality of second extra bit lines corresponding to second groups of the bit lines, each of which group has m bit lines (m is an integer), and extending across the word line, a plurality of second extra memory cells connected between the word line and the second extra bit lines for storing second checking information with respect to the second groups of the bit lines, an error detection circuit for comparing the information fed from the data memory cells with the contents of the first and second extra memory cells to detect errors, and a circuit responsive to an output from the error detection circuit for correcting the information fed from the data memory cells, the first extra bit lines being grouped correspondingly to the first groups of the bit lines, the sec~nd extra bit lines being grouped correspondingly to the second groups of the bit lines, each of the second groups of the second extra bit lines being composed of one of the first extra bit lines in each first group thereof.
The above and other objects, features and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying ~rawings in which certain preferred embodiments of the invention are shown by way of illustrative example.
Brief Description of the Drawings Figs. lA and lB are diagrammatic views showing the principles of horizontal and vertical parity checking systems applicable to a semiconductor memory device according to the 1~7~0~V
present invention;
Fig~ 2 is a block diagram illustrative of the fundamental arrangement of a semiconductor memory device constructed on the principles shown in Figs. lA and lB;
Fig. 2A is an enlarged circuit diagram of a data memory cell in the semiconductor memory device shown in Fig. 2;
Fig. 3 is a circuit diagram of a parity checking circuit in the semiconductor memory device illustrated in Fig.
2;
Fig. 4 is a circuit diagram of a parity bit generator in the semiconductor memory device; and Fig. 5 is a block diagram of a semiconductor memory device according to another embodiment of the present invention.
Detailed Description of the Preferred Embodiments Fig. lA shows horizontal parity bits a and vertical parity bits b which are appended horizontally and vertically respectively to a 4x4 matrix of 16 data bits. The parity checking system shown in Fig. lA is an even-parity-bit checking system in which the sum of l-bits in each horizontal row and vertical column is always even. For the sake of brevity, the even-parity-bit checking system will be relied on throughout the specification.
By transferring the data bits and the parity check bits a, b along the dotted-line arrows in Fig. lA, the two-dimensional matrix can be transformed into a one-di~ensional matrix as illustrated in Fig. lB. Any errors in upper 16 data ~t79060 bits out of the total of 24 bits in the one-dimensional matrix can detected in position by comparing groups of bits connected by solid lines with lower 8 parity bits. ThuS, a fixed or unfixed bit defect in any one of the upper 16 bits can be detected and corrected with ease. The foregoing arrangement is - indicative of the principle of the present invention based on which a sing~e erroneous bit can be corrected.
Fig. 2 illustrates a semiconductor memory device according to an embodiment of the present invention. The semi-conductor memory device includes a data memory cell unit 100for storing data bit information which comprises a matrix of data memory cells 10011 each including, as shown in Fig. 2A, a field-effect transistor 102 and a capacitor 103 connected in series between a bit line and the ground, the transistor 102 having a gate connected to a word line. The construction and operation of the data memory cells are well known in the art and hence will not be described in detail. The semiconductor memory device also has a parity cell unit 120 for storing horizontal and vertical parity check bit information. The parity cell unit 120 is composed of a first excess memory cell matrix 120h for storing horizontal parity check bit information, and a second excess memory cell matrix 120V for storing vertical parity check bit information. Each of the matrices 120h, 120V have a plurality of memory cells each of which is of the same construction as that of the data memory cell described above. A parity checking and correcting unit 6(~
130 comprises horizontal parity checking circuits 130hl-130hm, vertical parity checkin~ circuits 130V1-130Vk, a one-bit error correction circuit 132, and a data output circuit 134.
Each of the parity checking circuits 130hl-130hm, 130Vl-130Vm in the parity checking and correcting unit 130 is, for example, constructed as shown in Fig. 3. In this example, k (orm) is defined as 8 and each parity checking circuit is composed of eight EXCLUSIVE-OR gates 201-208. Each of the gates 201-204 is supplied with two bits out of eight data bits indicated at j. The gate 205 is supplied with outputs from the gates 201, 202, and the gate 206 is supplied with outputs from the gates 203, 204. The gates 205, 206 produce outputs that are fed to the gate 207. The gate 208 is supplied with an output from the gate 207 and a signal indica-tive of a parity check bit p. The gate 208 produces an output, which is delivered as an output from each parity checking circuit. The 8-bit data bit information j is supplied from the output of the data memory cell unit 100, that is, data bit lines corresponding to selected memory cells. Thus, the parity checking circuit 130hl receives data bit information from data bit lines 16011, 16021, ... 160kl, and a parity check bit p from a bit line 120hl in the first excess memory matrix 120h. The other parity checking cirucits 130h2-130hm are supplied with data bits and parity check bits over corresponding bit lines. The parity checking circuits 130Vl-~'79 ~ ~ ~
! 130Vk are supplied with data bi~s from the same data bit , lines, and with parity check bits p respectively fxom bit lines ¦ in the second excess memory cell matrix 120V.
As shown in Fig. 2, the one-bit error correction circuit 132 comprises AND gate 220ll-220k1, 12 k2~ 2201k-220km, and EXCLUSIVE-IR gates 3011-230kl~ 23012-230k2, 2301m 230km gate 220ll performs logical multiplication on, or ANDing of, an output from the horizontal parity checking circuit 130 and an output from the vertical parity checking circuit 130Vl. If the result of such logical multiplication is "O", it means that the contents of the data memory cells agree with those of the related horizontal and vertical parity check bits. Conversely, if the logical multiplication results is "1", it means that the contents of the data memory cells don1t agree with those of the related horizontal and vertical parity ¦ check bits. The AND gate 2201l delivers its output to the EXCLUSIVE-OR gate 23011. When the output of the AND gate 1 220ll is ~iO", the EXCLUSIVE-OR gate 2301l allows an output 2~ from the data memory cell unit lOO over the data bit line 160ll to pass therethrough as its own output. When the output of the AND gate 220ll is "l", the EXCLUSIVE-OR gate 230ll reverses an output from the data memory cell unit 100 over the data bit line 160ll, that is, corrects a one-bit error, and delivers such a reversed output to a subsequent stage. The other AND gates 22021-220km and associated ~7~
EXCLUSIVE-O~ ~ates 23021-230km operate in the same manner.
The data output circuit 134 serves to issue succes-si~-ely outputs or corrected data from the one-bit error correction circuit 132 based on bit selection signals.
The semiconductor memory de~ice also includes a data input circuit 140 for delivering data supplied from an outside processing circuit (not shown) only to selected memory cells in the data memory cell unit 100 based on bit selection signals BSl. The other unselected memory cells in the data memory cell unit 100 supplied by the data input circuit 140 with outputs from the one-bit error correction circuit 132. The data input circuit 140 has switch or gate circuits 140A
responsive to the bit selection signals BSl for selectively delivering the data ~rom the outside processing circuit and the bit information from the correction circuit 132 to the bit lines connected to the data memory cell unit 100. When the bit lines for memory cells in which new data are to be written are designated by the bit selection signals, the data input circuit 140 delivers exterior data to such selected bit lines and data from the correction circuit 132 to the other bit lines that are not selected. The semiconductor memory device includes word lines l50i-150in. The data bit lines 16011-160kl, 12 60k2, ... 1601m-160km jointly constitute lxm lines. The horizontal parity check bits are generated by over the data bit lines in groups of k bits, and hence the data bit lines are divided into m groups each for delivering k bits.
~'79(~6{3 The total number of the horizontal and vertical parity bit lines is k+m. The horizontal parity bit lines are divided into groups corresponding respectively to the data bit lines grouped 11 kl~ 16012-160k2, ... 1601m-160k , and the vertical parity bit lines are ~rouped into divisions corresponding respectively to the data bit lines grouped as 11' 1612 ~ 1601m, 16021, 16022 ... 160 160kl, 16k2 ' 160km -~orizontal parity check bit generators 170hl~170hm are provided respectively for the foregoing groups of horizon-tàl parity check bit lines, and vertical parity check bit generators 170Vl-170Vk are provided respectively for the above groups of vertical parity check bit lines.
The (kxm) data bit lines which are connected to the outputs of the data input circuit 140 and are divided into m groups each for k bits for forming horizontal parity bit information in k bits, are coupled to the horizontal parity check bit generators 170hl-170hm which are m in number.
The (kxmj data bit lines which are divided into k groups each for m bits for forming vertical parity bit information in m bits, are coupled to the vertical parity ch~ck bit senerators 170Vl-170Vk which are k in number.
As shown in Fig. 4, in the case of k (or m) = 8, each of the parity check bit generators 170hl~170hmr 170Vl-170Vk comprises seven EXCLUSIVE-OR gates 241-247 which are connected in the same arrangement as that of the ~'7~3~6~
EXCLUSIVE-OR gates 201-207 as enclosed by the dotted line in each parity checking circuit illustrated in Fig. 3. The EXCLUSIVE-O~ gates 241-244 are supplied with the inputs j which are fed also to the EXCLUSIVE-OR gates 201-204. The first excess memory cell matrix 120h in the parity cell unit 120 for storing the horizontal parity check bit information includes m excess bit lines corresponding respectively to the m groups of data bit lines for creating the h~orizontal parity check bit information. The second excess memory cell matrix 120V for storing the vertical parity bit check information includes k excess bit lines corresponding respectively to the k groups of data bit lines for forming the vertical parity check bit information. These excess bit lines are coupled to the word lines 150il-150in by excess memory cells in the first and second memory cell matrices 120h, 120V of the parity cell unit 120.
When any one of the word lines 150il-150i~ is energized, data bit information of (kxm~ bits is read out of the data memory cells which are connected ~o the activated word line and led as m groups of data bit information each in k bits, correspondiny to the grups o (kxm) data bit lines, to the m horizontal parity checking circuits 130hl-130hm, respectively. The (kxm)-bit data information as divided in k groups each in m bits is delivered as grouped to the vertical pàrity checking circuits 130Vl-130Vk. The m-bit horizontal parity check bit information and the k-bit vertical parity ~t7~0 check bit information, which are read simultaneously with the reading of the (kxm)-bit data information, are supplied as checking information to the parity checking circuits 130hl-130hm, 130Vl-130Vk for the corresponding groups.
Output signals from the horizontal parity checking circits 130hl-130hm and those from the vertical parity checking circuits 130Vl-130Vk are delivered as inputs respectively to the AND gates 22011-220km of the correction circuit 132 to detect whether there is no error horizontally and vertically in the data bit information read from the data memory cell unit 100. The AND gates 22011-220km are (kxm) in number and divided into groups each containing k gates. Each of the AND
gates, grouped as 22011-220kl, 22012-220k2, .--2201m-220km is supplied at one of its inputs with an output signal from one of the horizontal parity checking circuits 130hl-130hm, and is also supplied at the other input with an output from one of the vertical parity checking circuits 130Vl-130Vk. This arrangement determines whether there is no error in each delivered piece of data bi-t information horizontally and vertically. With the even-parity-bit checking system employed, the horizontal parity checking circuits 130hl-130hm will produce an output signal of "1" where an error is detected upon horizontal checking, and the vertical parity checking ~ircuits 130~1-130Vk will generate an output signal of "l" where an error is detected upon vertical checking.
~7~
The (kxm) AND gates 22011-220km deliver their output signals to the (kxm) EXCLUSI~E-OR gates 23011-230km, respectively. The EXCLUSIVE-OR gates 23011-230km will reverse the logical values of the data bit information fed from the data memory cell unit 100 only when such supplied data bit information contains an error in both the horizontal and vertical directions. The output signals from the EXCLUSIVE-OR
gates 23011-230km go to the output circuit 134 and simul-taneously to the input circuit 140 as error-corrected data bit in~ormation by way of feedback paths 180.
Data information operation of the circuit arrangement shown in Fig. 2 will be described. When a desired one of the word lines 150il-150in is activated, (kxm)-bit data bit information is read in parallel from a corresponding one of the groups of data memory cells in the data memory cell unit 100, which are connected to the selected word line, and at the same time, parallel m-bit horizontal parity check bit information and parallel k-bit vertical parity check bit information are read from the excess memory cells in the excess memory cell matrices 120h, 120V, which are connected to the selected word line. The (kxm)-bit data bit information thus read from the memory cell unit 100 is supplied one bit at a time to the EXCLUSIVE-OR gates 23011-230km in the error correction circuit 132, and is also supplied as grouped to the horizontal and vertical parity checking circuits 130hl-130hm, 130Vl-130Vk. The horizontal parity checking circuits 130hl-130hm compare the supplied data bit information with the horizontal pari~y check bit information read from the memory cell matrix 120h to determine whether there is an error horizontàlly/ and produce signals of "1" indicative o~
such an error when the error is included. Likewise, the vertical parity checking circuits 130Vl-130Vk compares the supplied data bit information with the vertical-parity check bit information read from the memory cell matrix 120V to determine whether an error is included verticaly, and generate signals of "1" indicative of such an error when the error takes place. The output signals from the horizontal parity checking circuits 130hl-130hm and the vertical parity checking circuits 130Vl-130Vk are delivered to the error correction circuit 132.
An instance in which the data bit information supplied to the EXCLUSIVE-OR gate 23011 contains an error will be described. The output signals from the horizontaL parity checking circuit 130hl and the vertical parity checking circuit 130Vl are "1". The logical value of only the data bit information fed to the EXCLUSIVE-OR gate 230l1 is reversedt whereas the other data bit information is supplied as it is to the output circuit 134. The correction circuit 132 produces as outputs error-corrected data bit information. The error-corrected data bit information is delivered as an output by the output circuit 134 with desired one or more bits selected by ~he bit selection signal BS2. At the same time, the output signals from the error correction circuit 132 are fed back via feedback lines 180 to the input circuit 140, ~rom which the signals are stored again in the original memory cell positions in the data memory cell unit 100. Upon storing again such signals, horizontal and vertical parity check bit information based on the error-corrected data bit information is written in corresponding extra memory cells in the first and second extra memory cell matrices 120h, 120V.
New data bit information supplied from the exterior source will be written in as follows: The bit selection signal BSl is supplied to the input circuit 140 to indicate in which data memory cell on a desired word line new data should be written. The word line to which is connected the data memory cell in which the new data is to be written is energized at first, for thereby reading all of the data bit information from the data memory cells coupled to that word line in a manner similar to that for the foregoing data reading operation.
Then, data bit information fed back from the error correction circuit 132 is caused to be stored again in the other data memory cells than the data memory cell in which the new data should be stored. Simultaneously, the data bit information from the exterior source is stored in the desired data memory cell. At this time, horizontal and vertical parity check bit information based on the new data bit information from the exterior source and the data bit information fed back from the error correction circuit 132 is formed in the parity check bit ~7~ O~ ~
170hl 170hm' 170vl~l70vk/ and stored in the extra memory cell matrices 120h, 120V.
The semiconductor memory device thus constructed has the following advantages:
~1) Horizontal and vertical parity checking can be performed at one time within the memory by activating a word line, that is, one-dimensional parity checking can be carried out. Bit errors produced in the memory device are thus fewer than those experienced with conventional memory devices, with the result that the effective yield of semiconductor memory devices can be increased or the semiconductor memory devices will operate with improved reliability. For example, assuming that the yield is expressed by the probability that the number of defective bits per word line with respect to the rate of occurence complete non-defective memory devices is 1 or less, the yields of conventional memory devices with no error correction circuits are 1~, 5%, and 10%, whereas corresponding yields of memory devices of the present invention are 25~, 41~, and 50% respectively. Therefore, the yields of semiconductor memory devices according to the present invention are much higher than the pr~ior yields, and are substantially e~ual to those of peripheral circuits for memory devices, which can be manufactured on the current semiconductor fabrication technol-ogy. The rate of increase of reliability of the semiconductor memory device will be described with reference to soft errors caused by alpha rays. The rate of occurence of a soft error in 1~79(~
an LSI memory device with 1 Mb having no error correction circuit can be determined by the probability that one alpha-ray particle hits a single memory cell. With the present invention, the same rate can be determined by the probability that one alpha-ray particle impinges upon two or more memory cells within an error correction period. For a 1 Mb RAM as an example, a rate of occurence of a soft error in a conven-tional semiconductor memory device is 103 FIT (FIT=10 9/
hour) whereas a corresponding error occurence rate in a semi-conductor memory device of the present invention is 10 FIT, and another prior error occurence rate is 106 FIT while a corresponding error occurence rate according to the present invention is 10 2 FIT. The rate of occurence of soft errors in the semiconductor memory device of the invention is therefore quite reduced.
(2) With the arrangement of the present invention, most of an additional circuit required for correcting bit errors is in the parity cell unit, and the number of gates required in the parity checking and correcting unit is on the order of 4000 for a 1 Mb RAM. The ratio of the ~parity cell unit to the memory cell unit is 2 J~where N2 is the memory capacity, and hence becomes smaller as the memory capacity grows larger. The time interval ta required for error correction is given by:
ta = (3 + log2 ~) x ~ t where N is the square root of the memory capacity (N2=memory l~t7~
eapacity), and Q t is the delay time per gate. The error correction time for a 1 Mb RAM with ~ t=2 ns is 16 ns. with the added error correction circuit being small in scale according to the present invention, an increase in electric power consumption due to the added eircuit is expeeted to amount to lO mW or less for a 1 Mb RAM. Such a small inerease in the consumed electric power-does not substantially impair the memory performance. The semieonductor memory device aceording to the present invention is therefore advantageous in that the memory deviee itself ean be compact in size, is eapable of eorreeting bit errors within a short period of time, and does not involve a large increase in electric power eonsumption.
The semieonductor memory deviee aecording to the foregoing embodiment fails to correct two or more bit errors in one group out of the horizontal m bit line groups, or two or more bit errors in one group out of the vertical k bit line groups. ~owever, the semiconductor memory device can have a function of correcting two or more bit errors by causing code information eapable of detecting two or more bit errors, instead of parity eheek bit information, to be stored in the extra memory cell matrices 120h, 120V.
Fig. 5 shows a semiconductor memory device according to another embodiment of the present invention, particularly a semiconductor memory device of plural words x 1 bit type.
Identical or corresponding parts in Fig. 5 are denoted by 9(~0 identical or corresponding re~erence characters in Fig. 2. A
data memory cell matrix or unit 100 and a parity cell 120 composed of first and second extra memory matrices 120h, 120V are of the same construction of those illustrated in Fig. 2. Therefore, the data memory cell unit 100 comprises a (kxm)-bit matrix arranged one-dimensionally in a pattern as shown in Fig. lB, with memory cells being connected to common word lines. There are m groups of bit lines 16011-160kl, 12 6k2' 1601m- 160km, and each group consisting of k bits.
Selectors 3001 300m are provided respectively for the m groups of data memory cells in the data memory cell unit 100. Now, suppose that several upper bits or several lower bits within bits of the external address signal are used as an address signal Sl and the remaining bits as an address signal S2. Each selector is connected to the bit lines in a corres-ponding group of data memory cells, and serves to select one-bit data bit in~ormation from k-bit data bit information in response to the signal Sl. Where information i.n a memory celll for example, information stored in the memory cell connected to the bit line 16011 and the word line 150il is read out, the address signal Sl is supplied to the selectors 3001r 32 ... 300m to select the uppermost bit line 11' 6012, 16013 ... 1601m of each o~ the in bit groups, each of which is constituted by k bit lines. As an example, the bit line 16011 is connected to the output of the 7'3~
selector 3001, the bit line 16012 is connected to the output of the selector 32~ and the bit line 1601m is connected to the output of the selector 300m. Selected information of the memory cells connected to-these bit lines and the word line 150il is outputted to the vertical parity check circuit 310. Selected output signals from the selectors are supplied as data bit information for verticl parity checking to a vertical parity checking circuit 310. The vertical parity checking circuit 310 is composed of a plurality of EXCLUSIVE-OR gates as with the above embodiment of Fig. 2, and is receptive of, besides the outputs from the selectors, a corresponding output from a vertical parity cell matrix 120V
via a vertical parity check bit generator 420 described in detail later on. The vertical parity checking circuit 310 produces an output as a result of vertical parity checking.
A selector 320 serves to select grouped k-bit data bit inforamtion from the (kxm)-bit data bit information supplied from the data memory cell unit 100 in response to an address signal S2. That is, the address signal S2 i-s supplied to the selector 320 to select k bit lines 16011, 16021, 160kl, each of which constitutes the uppermost bit line group. Selected information of the memory cells connected to these bit ~ines and the word line 150il is outputted to the horizontal parity check circuit 340 from the selector 320.
Data bit information from a selected group of bit lines is delivered as an output from the selector 320 to a selector 330 ~ ~'79 ~ ~ ~
and to a horizontal parity checking circuit 340 as data bit information for hori~ontal parity checkingO The horizontal parity checking circuit 340 is composed of a plurality of ~ .
EXCLUSIVE-OR gates as with the corresponding circuit of the foregoing embodiment. The horizontal parity checking cirucit 340 also receives an output from a horizontal parity cell matrix 120h via a horizontl parity check bit generator 410, and produces an output as a result of horizontal parity checking.
The selector 330 is in response to an address signal Sl for selecting data bit information fed from the groups of bit lines.
Outputs from the parity checking circuits 310, 340 and an output from the selector 330 are supplied to a one-bit error correction circuit 350. The error correction circuit 340 comprises an AND gate 352 receptive of the output from the horizontal parity checking circuit 340 and the output from the vertical parity checking circuit 310, and an EXCLU~IVE-OR gate 354 receptive of an output from the AND gate 352 and an output from the selector 330. The error correction circuit 350 serves to reverse the output from the selector 330 when both of the outputs from the parity checking circuits 340, 310 are "1" r and issues such a reversed output. The output from the error correction circuit 350 is delivered out of the memory devicea The output from the error correction circuit 350, that is, error-corrected data bit information is fed back to the input of the error correction circuit 350 via a feedback path 370. The error-corrected data bit information thus fed back is stored again into desired memory cells or storage positions in the data memory cell unit 100 through the selectors 330, 320.
When it is necessary to write new input data in rela-. . .
tion to t~e above re-storlng operation, such new lnput data is supplied via a switch 401 in a data input circuit 400 to the output of the selector 330 and then stored via the selectors 330, 320 into desired memory cells in the data memory cell unit 100. Simultaneously with the writing of the new data in the data memor~ cell unit 100, the following parity data generating operation is performed.
The input circuit 400 includes an EXCLUSIVE-OR gate 403 in addition to the switch 401. The EXCLUSIVB-OR gate 403 is receptive of new input data and the output from the one-bit error correction circuit 350 to determine whether the new write data from the exterior source is different from the previous data. If different, then the EXCLUSIVE-OR gate 403 delivers an output, and horizontal and vertical parity check bit informa-tion related to the new data is supplied to horizontal and vertical parity check bit generators 410, 420.
The horizontal parity check bit gener-ator 410 comprises an EXC~USIVE-OR gate 411, a gate or switch 413, and a selector 415. The EXCLUSIVE-OR gate 411 is supplied with an output from the gate 403 in the data input circuit 400 and an output from the selector 415. when the gate 413 receives the control signal CSl, an output of the gate 411 is stored via the selector 415 into a corresponding memory cell in the first l'~t7~
extra memory matrix 120h as horizontal parity check bit information. The gate 411 issues an output of "1" only when the inputs thereto are different from each other.
.. . . . . .
- ~ ~ The vertical parity check bit generator -~2a comprises an EXCLUSIVE-OR ~ate 421, a gate or switch 423, and a selector 425. the EXCLUSIVE-OR gate 421 is supplied with an output from the gate 403 in the data input circuit 400 and an output from the selector 415. When the control signal CSl is fed to the gate 423, an output of the gate 41 is stored as vertical parity check bit information ito a corresponding memory cell in the second extra memory cell matrix 120V via the selector 425.
The gate 421 produces an output of "1" only when the inputs thereto are different from each other.
With the arrangement according to the embodiment shown in Fig. 5, both fixed and unfixed bit errors can be saved or corrected. Particularly, the semiconductor memory device illus~rated in Fig. 5 includes selectors for selecting data bit information necessary ~or generating horizontal and vertical parity check bit information and for horizontal and vertical parity checking, such that the wiring area and peripheral circuits needed can be smaller than that in the semiconductor memory device of Fig. 2. For example, the number of the gates constituting the parity checking/correctng unit becomes about one thirty-second (32th) of that of the embodiment shown in Fig. 2 that is about 140 gates. As described aboe, the semiconductor memory devices according to the present invention ~7~0~0 are advantageous in that they can save or correct both Eixed and unfixed bit errors.
Although certain preferred embodiments have been shown and described in detail, it should be understood that various changes and modifications may be made therein without departing from the scope of the appended claims.
Claims (7)
1. A semiconductor memory device comprising:
at least one word line;
a plurality of bit lines extending across said word line;
a data memory cell unit including a plurality of data memory cells connected between said word line and said bit lines for storing information;
a plurality of first extra bit lines corresponding to first groups of the bit lines, each of which group has k bit lines (k is an integer), and extending across said word line;
a plurality of first extra memory cells connected between said word line and said first extra bit lines for storing first checking information with respect to the first groups of the bit lines;
a plurality of second extra bit lines corresponding to second groups of the bit lines, each of which group has m bit lines (m is an integer), and extending across said word line;
a plurality of second extra memory cells connected between said word line and said second extra bit lines for storing second checking information with respect to the second groups of the bit lines;
an error detection circuit for comparing the informa-tion fed from the data memory cells with the contents of said first and second extra memory cells to detect errors;
a circuit responsive to an output from said error detection circuit for correcting the information fed from said data memory cells; and said first extra bit lines being grouped correspond-ingly to said first gorups of the bit lines, said second extra bit lines being gruped correspondingly to said second groups of the bit lines, each of the second groups of the second extra bit lines being composed of one of the first extra bit lines in each first grup thereof.
at least one word line;
a plurality of bit lines extending across said word line;
a data memory cell unit including a plurality of data memory cells connected between said word line and said bit lines for storing information;
a plurality of first extra bit lines corresponding to first groups of the bit lines, each of which group has k bit lines (k is an integer), and extending across said word line;
a plurality of first extra memory cells connected between said word line and said first extra bit lines for storing first checking information with respect to the first groups of the bit lines;
a plurality of second extra bit lines corresponding to second groups of the bit lines, each of which group has m bit lines (m is an integer), and extending across said word line;
a plurality of second extra memory cells connected between said word line and said second extra bit lines for storing second checking information with respect to the second groups of the bit lines;
an error detection circuit for comparing the informa-tion fed from the data memory cells with the contents of said first and second extra memory cells to detect errors;
a circuit responsive to an output from said error detection circuit for correcting the information fed from said data memory cells; and said first extra bit lines being grouped correspond-ingly to said first gorups of the bit lines, said second extra bit lines being gruped correspondingly to said second groups of the bit lines, each of the second groups of the second extra bit lines being composed of one of the first extra bit lines in each first grup thereof.
2. A semiconductor memory device according to claim 1, wherein said first extra memory cells being capable of storing horizontal parity check bit information for said data memory cell unit, and said second extra memory cell being capable of storing vertical parity check bit information for said data memory cell unit.
3. A semiconductor memory device according to claim 1, further including horizontal and vertical parity check bit generators connected to said bit lines which are grouped differently for storing horizontal and vertical parity check bit information respectively into said first and second extra memory cells.
4. A semiconductor memory device according to claim 1, including a data input circuit for selectively supplying data from an exterior source and an output from said correcting cirucit to each of said bit lines.
5. A semiconductor memory device according to claim 1, wherei said error detection circuit comprises a horizontal parity checking circuit for comparing information from said data memory cells with horizontal parity check bit information from said first memory cells, and a vertical parity checking circuit for comparing information from said data memory cells with vertical parity check bit information from said second extra memory cells, the arrangement being that said correcting circuit corrects information from said data memory cells when outputs from said horizontal and vertical parity checking circuits agree with eac other.
6. A semiconductor memory device according to claim 5, wherein said correcting circuit comprises a plurality of first selectors for selecting data bit lines which constitute said second groups respectively from said first groups of the data bit lines and for connecting the selected data bit lines to said vertical parity checking ciruit, a second selector for selecting one group out of said first groups of the data bit lines, and third and fourth selectors for selecting first and second extra bit lines corresponding to said selected data bit lines from said plurality of first and second extra bit lines for said first and second extra memory cells and for connenct-ing the selected first and second extra bit lines respectively to said horizontl and vertical parity checking circuits.
7. A semiconductor memory device according to claim 6, wherein said correcting circuit includes a fifth selector for successively selecting outputs from said second selector and for connecting the selected outputs to the error correcting circuit.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP56037223A JPS6042560B2 (en) | 1981-03-17 | 1981-03-17 | semiconductor storage device |
| JP37223/81 | 1981-03-17 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1179060A true CA1179060A (en) | 1984-12-04 |
Family
ID=12491588
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000398528A Expired CA1179060A (en) | 1981-03-17 | 1982-03-16 | Semiconductor memory device |
Country Status (7)
| Country | Link |
|---|---|
| US (1) | US4456980A (en) |
| JP (1) | JPS6042560B2 (en) |
| CA (1) | CA1179060A (en) |
| DE (1) | DE3209679A1 (en) |
| FR (1) | FR2502377B1 (en) |
| GB (1) | GB2097157B (en) |
| NL (1) | NL190708C (en) |
Families Citing this family (23)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JPS59213100A (en) * | 1983-05-16 | 1984-12-01 | Nippon Telegr & Teleph Corp <Ntt> | Semiconductor storage device |
| US4653051A (en) * | 1983-09-14 | 1987-03-24 | Matsushita Electric Industrial Co., Ltd. | Apparatus for detecting and correcting errors on product codes |
| US4599709A (en) * | 1984-02-17 | 1986-07-08 | At&T Bell Laboratories | Byte organized static memory |
| US4612640A (en) * | 1984-02-21 | 1986-09-16 | Seeq Technology, Inc. | Error checking and correction circuitry for use with an electrically-programmable and electrically-erasable memory array |
| JPS60183653A (en) * | 1984-03-01 | 1985-09-19 | Toshiba Corp | Memory provided with bit error detecting function |
| JPS61264599A (en) * | 1985-05-16 | 1986-11-22 | Fujitsu Ltd | Semiconductor memory device |
| JPS61289600A (en) * | 1985-06-17 | 1986-12-19 | Fujitsu Ltd | Semiconductor memory device |
| JPS6246357A (en) * | 1985-08-23 | 1987-02-28 | Hitachi Vlsi Eng Corp | Semiconductor memory device |
| US4747080A (en) * | 1985-11-12 | 1988-05-24 | Nippon Telegraph & Telephone Corporation | Semiconductor memory having self correction function |
| US4845714A (en) * | 1987-06-08 | 1989-07-04 | Exabyte Corporation | Multiple pass error correction process and apparatus for product codes |
| DE3843564A1 (en) * | 1988-12-23 | 1990-06-28 | Standard Elektrik Lorenz Ag | METHOD FOR CHECKING CONNECTION AND / OR SWITCHING DEVICES AND / OR CABLES |
| US5515383A (en) * | 1991-05-28 | 1996-05-07 | The Boeing Company | Built-in self-test system and method for self test of an integrated circuit |
| US5513192A (en) * | 1992-08-28 | 1996-04-30 | Sun Microsystems, Inc. | Fault tolerant disk drive system with error detection and correction |
| ITMI20020260A1 (en) * | 2002-02-12 | 2003-08-12 | Ausimont Spa | WATER DISPERSIONS OF FLUOROPOLYMERS |
| US7010741B2 (en) | 2002-10-29 | 2006-03-07 | Mosaid Technologies | Method and circuit for error correction in CAM cells |
| CA2447204C (en) * | 2002-11-29 | 2010-03-23 | Memory Management Services Ltd. | Error correction scheme for memory |
| JP2005195113A (en) * | 2004-01-08 | 2005-07-21 | Toyota Motor Corp | Structure for sealing air-tight space inside engine for vehicle, and engine for vehicle |
| JP4413091B2 (en) * | 2004-06-29 | 2010-02-10 | 株式会社ルネサステクノロジ | Semiconductor device |
| KR100694407B1 (en) * | 2005-04-21 | 2007-03-12 | 주식회사 하이닉스반도체 | Non-volatile ferroelectric memory device with circuit for correcting fail cell |
| US20060256615A1 (en) * | 2005-05-10 | 2006-11-16 | Larson Thane M | Horizontal and vertical error correction coding (ECC) system and method |
| US8381052B2 (en) * | 2009-11-10 | 2013-02-19 | International Business Machines Corporation | Circuit and method for efficient memory repair |
| KR101212759B1 (en) * | 2010-10-29 | 2012-12-14 | 에스케이하이닉스 주식회사 | Data transfer method with data error check, semiconductor memory and memory system with data error check |
| JP2016018569A (en) * | 2014-07-04 | 2016-02-01 | 株式会社ソシオネクスト | Semiconductor integrated circuit |
Family Cites Families (6)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3067407A (en) * | 1959-12-24 | 1962-12-04 | Ibm | Cathode ray tube printer |
| US3242461A (en) * | 1961-12-28 | 1966-03-22 | Teletype Corp | Error detection system |
| US4016409A (en) * | 1976-03-01 | 1977-04-05 | Burroughs Corporation | Longitudinal parity generator for use with a memory |
| US4183463A (en) * | 1978-07-31 | 1980-01-15 | Sperry Rand Corporation | RAM error correction using two dimensional parity checking |
| US4228528B2 (en) * | 1979-02-09 | 1992-10-06 | Memory with redundant rows and columns | |
| US4365332A (en) * | 1980-11-03 | 1982-12-21 | Fairchild Camera And Instrument Corp. | Method and circuitry for correcting errors in recirculating memories |
-
1981
- 1981-03-17 JP JP56037223A patent/JPS6042560B2/en not_active Expired
-
1982
- 1982-03-15 US US06/357,840 patent/US4456980A/en not_active Expired - Lifetime
- 1982-03-15 GB GB8207459A patent/GB2097157B/en not_active Expired
- 1982-03-16 FR FR8204382A patent/FR2502377B1/en not_active Expired
- 1982-03-16 CA CA000398528A patent/CA1179060A/en not_active Expired
- 1982-03-16 NL NL8201081A patent/NL190708C/en not_active IP Right Cessation
- 1982-03-17 DE DE19823209679 patent/DE3209679A1/en active Granted
Also Published As
| Publication number | Publication date |
|---|---|
| US4456980A (en) | 1984-06-26 |
| JPS6042560B2 (en) | 1985-09-24 |
| FR2502377B1 (en) | 1988-06-24 |
| GB2097157A (en) | 1982-10-27 |
| DE3209679C2 (en) | 1988-01-28 |
| NL8201081A (en) | 1982-10-18 |
| FR2502377A1 (en) | 1982-09-24 |
| NL190708B (en) | 1994-02-01 |
| GB2097157B (en) | 1985-02-20 |
| DE3209679A1 (en) | 1983-01-20 |
| JPS57152597A (en) | 1982-09-20 |
| NL190708C (en) | 1994-07-01 |
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