Abstract:
A semiconductor storage device can improve probability of relieving of defective cell. The semiconductor storage device includes a redundancy cell for relieving a defective cell when the defective cell is found during fabrication process of a memory cell, a redundancy judgment circuit making judgment whether an input address is a column address of the defective cell or not and redundancy column selection lines for making the redundancy cell active when the redundancy judgment circuit makes judgment that the input address is the column address of the defective cell. The semiconductor storage device further includes means for dividing the redundancy cell connected to one redundancy column selection line into a plurality of divided redundancy cells and assigning the column address of the defective cell to each of divided redundancy cells as relieving address.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a semiconductor storage device. More particularly, the invention relates to a semiconductor storage device which enables relieving by programming a column address of a defective cell in a redundancy judgment circuit when a defective memory cell is found during fabrication process. 
     2. Description of the Related Art 
     Conventionally, in the semiconductor storage device of this type is constructed with a column decoder  10 , a redundancy column decoders  2  and  3 , a row decoder  4 , a memory cell array  20 , an amplifier circuit  6 , a redundancy judgment circuits  11  and  12 , an internal clock generating circuit  31 , a command decoder  32 , an internal address generating circuit  33 , a column system circuit  34 , an input/output circuits  35  to  38  and a row system control signal generating circuit  39 , as shown in FIG.  9 . 
     The internal clock generating circuit  31  generates an internal clock ICLK on the basis of a reference clock CLK input externally. The command decoder  32  inputs /RAS, /CAS, /WE and /CS. The row system control signal generating circuit  39  receives a result of decoding from the command decoder  32  to generate a row system control signal. 
     The column system circuit  34  receives a result of decoding from the command decoder  32  to generate a column system control signal. An internal address generator circuit  33  is responsive to an external address input ADD and the result of decoding from the command decoder  32  to generate a row address and a column address in synchronism with the internal clock ICLK. 
     The row decoder  4  is responsive to the row system control signal and the row address to select one of a plurality of word lines WL depending upon the row address and also one of a plurality of a plate selection signals (not shown). 
     The redundancy judgment circuits  11  and  12  are responsive to the column address to make judgment whether the input column address is a preliminarily programmed redundancy address or not to output redundancy judgment signals R 1  and R 2 . 
     The column decoder  10  is responsive to the column address and the redundancy judgment signals R 1  and R 2  not to select or select one of a plurality of column selection lines depending upon the column address. The redundancy column decoders  2  and  3  are responsive to the redundancy judgment signals R 1  and R 2  for determining whether the corresponding redundancy column selection line is to be selected or not. 
     The memory cell array  20  is connected to the word lines WL, the column selection lines, the redundancy selection line and an IO (input/output) line for receiving inputs therethrough. The input/output circuits  35  to  38  are connected one of input/output terminals DQ 0  to DQ 3  to read out data on read/write buses RWBUS 0  to RWBUS 3  or write data in the read/write buses RWBUS 0  to RWBUS 3  corresponding to output of the column system circuit  34  and whereby to perform reading and writing. The amplifier circuit  6  is connected to the column system circuit  34  to receive output therefrom and also to the I 0  line and the read/write buses RWBUS 0  to RWBUS 3 . 
     As shown in FIG. 10, the memory cell array  20  is constructed with a plurality of plates (plate  1 , plate  2  . . . ). Each plate is connected to a plurality of word lines WL and a plurality of bit line pairs which are, in turn, connected to sense amplifiers (SA). Each column line and each redundancy column line are connected to four sense amplifiers per plate, respectively. 
     On the other hand, the sense amplifier SA receives a plate selection signal (plate selection signal  1 , plate selection signal  2  . . . ) corresponding to each plate on the bit line pair connected thereto. Four sense amplifiers connected to the same column line or the same redundancy column selection line in each plate are connected to respectively different IO lines. 
     Four IO lines wired to each plate are connected to respectively corresponding IO lines of other plate output side of the memory cell array  20 , and are also connected to the amplifier circuit  6 . To the bit line pair and the work line WL, a plurality of memory cells are connected. 
     The redundancy column decoders  2  and  3  receives respective redundancy judgment signals R 1  and R 2 , as shown in FIG. 11, and are constructed with buffer circuits (BUF)  2   a  and  3   a  driving one redundancy column selection line. 
     The column decoder  10  is constructed with an OR circuit  10   a  deriving an OR of the redundancy judgment signals R 1  and R 2 , AND circuits  10   b - 1  to  10   b -n deriving AND of an output of the OR circuit  10   a  and the column address. A plurality of column addresses input to respective AND circuits  10   b - 1  to  10   b -n have different combination of high (High)/low (Low) per address so as to select only one column selection line. 
     Next, discussion will be given for operation of the conventional semiconductor storage device with reference to FIG.  12 . The semiconductor storage device receives active command upon rising of the clock of cycle C 1  (not shown) to select one of the word lines WL of row address corresponding to the data on the address terminal and one of the plate selection signals selecting the plate including the selected word line WL. 
     Subsequently, upon rising the clock of cycle C 2 , the read command is input and, at this time, if the data of the address terminal is a normal column address not preliminarily programmed in the redundancy judgment circuits  11  and  12 , both of the redundancy judgment signals R 1  and R 2  are redundancy non-selected condition (low level), one column selection line corresponding to the data of the address terminal is selected (low level), and the redundancy selection line is not selected (low level). 
     Then, upon rising of the clock of the cycle C 3 , the semiconductor storage device receives the read command and if the data of the address terminals is the redundancy column address preliminarily programmed in the redundancy judgment circuit  11 , the programmed redundancy judgment signal R 1  output from the redundancy judgment circuit  11  becomes selected condition (high level), and all of the column selection lines becomes non-selected state (low level). Also, the redundancy selection line corresponding to the redundancy judgment signal R 1  becomes selected condition (high level), and other redundancy column selection lines are not selected (low level). 
     Furthermore, upon rising of the clock of the cycle C 4 , the semiconductor storage device receives the read command and if the data of the address terminals is the redundancy column address preliminarily programmed in the redundancy judgment circuit  11 , the programmed redundancy judgment signal R 2  output from the redundancy judgment circuit  11  becomes selected condition (high level), and all of the column selection lines becomes non-selected state (low level). Also, the redundancy selection line corresponding to the redundancy judgment signal R 2  becomes selected condition (high level), and other redundancy column selection lines are not selected (low level). 
     The column selection line corresponding to the programmed column address is not selected even when the corresponding address is input, and in place, the redundancy column selection line is selected. Therefore, the bit line and the sense amplifier connected to the defective cell are not used, and through the sense amplifier and bit line connected to the redundancy column selection line, the redundancy memory cell is selected. 
     Accordingly, even when defective memory cell is found during fabrication process of the semiconductor storage device, it can be relieved by programming the column address of the defective cell in the redundancy judgment circuits  11  and  12 . 
     On the other hand, in each read command input cycle, data amplified by selected one of the sense amplifiers is transmitted to each IO line, and then, is input to the amplifier circuit  6 . Data further amplified by the amplifier circuit  6  is transmitted to the input/output circuits  35  to  38  through the read/write buses RWBUS 0  to RWBUS 3 , and then output to the input/output terminals DQ 0  to DQ 3  at a predetermined timing. 
     On the other hand, upon inputting of the write command, data input to the input/output terminals DQ 0  to DQ 3  is transmitted to the amplifier circuit  6  via the input/output circuits  35  to  38  and the read/write buses RWBUS 0  to RWBUS 3 , and is written in selected one of the sense amplifiers via the IO line and subsequently written to the selected memory cell via connected bit line pair. 
     In the foregoing semiconductor storage device, even when the defective memory cell is found in the fabrication process, the storage device can be relieved by programming the column address of the defective cell in the redundancy judgment circuit. However, if defective cells are caused beyond a number of the redundancy selection lines connected to the redundancy judgment circuit, the foregoing measure will not work. 
     SUMMARY OF THE INVENTION 
     The present invention has been worked out in view of the problem set forth above. It is therefore an object of the present invention to provide a semiconductor storage device which can improve probability of relieving of defective cell. 
     According to one aspect of the present invention, a semiconductor storage device comprises: 
     a redundancy cell for relieving a defective cell when the defective cell is found during fabrication process of a memory cell; 
     a redundancy judgment circuit making judgment whether an input address is a column address of the defective cell or not; 
     redundancy column selection lines for making the redundancy cell active when the redundancy judgment circuit makes judgment that the input address is the column address of the defective cell; 
     means for dividing the redundancy cell connected to one redundancy column selection line into a plurality of divided redundancy cells and assigning the column address of the defective cell to each of divided redundancy cells as relieving address. 
     Namely, the semiconductor storage device according to the present invention is provided with a plurality of redundancy judgment circuit for permitting programming of a plurality of relieving address for one redundancy column (COLUMN). 
     By this, with among a plurality of memory cells selected by one redundancy column selection line and other redundancy cell, relieving with other redundancy cell becomes possible to improve probability of relieving of the defective cell. 
     In the preferred construction, a plurality of the redundancy judgment circuits are provided for making judgment whether the input address is the relieving address assigned for each of the divided redundancy cell. The semiconductor storage device may further comprise logic operation means for performing logical operation for respective outputs of a plurality of the redundancy judgment circuits and means for selecting any one of a plurality of redundancy column lines depending upon a result of operation of the logic operation means. The logic operation means may perform operation of logical sum of outputs of the plurality of redundancy judgment circuits. 
     The semiconductor storage device may further comprise means for switching between input/output line of the redundancy cell in the memory cell and normal input/output line depending upon a result of judgment by the redundancy judgment circuit. The switching means may be constructed for switching the input/output line of the redundancy cell and the input/output line of the normal cell. The semiconductor storage device may be constructed to select the column selection line of the normal cell irrespective of the result of judgment of the redundancy judgment circuit. 
     A plurality of redundancy judgment circuits are provided corresponding to number of division of the redundancy cell. The redundancy cell may be divided into two, the redundancy judgment circuit in number of double of the redundancy column selection lines are provided. When the redundancy cell is divided into four, the redundancy judgment circuit in number of four times of the redundancy column selection lines may be provided. The means for selecting one of the plurality of redundancy column selection lines comprises a buffer circuit for driving selected redundancy column selection line. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be understood more fully from the detailed description given hereinafter with reference to the accompanying drawings of the preferred embodiment of the present invention, which, however, should not be taken to be limitative to the present invention, but are for explanation and understanding only. 
     In the drawings: 
     FIG. 1 is a circuit diagram showing one embodiment of a semiconductor storage device according to the present invention; 
     FIG. 2 is an illustration showing a detailed construction of a memory cell array of FIG. 1; 
     FIG. 3 is a circuit diagram showing a detailed construction of a column decoder and a redundancy column decoder of FIG. 1; 
     FIG. 4 is a timing chart showing an operation of one embodiment of the semiconductor storage device according to the present invention; 
     FIG. 5 is a circuit diagram showing a construction of another embodiment of the semiconductor storage device according to the present invention; 
     FIG. 6 is a circuit diagram showing a construction of another embodiment of the semiconductor storage device according to the present invention; 
     FIG. 7 is a timing chart showing an operation of another embodiment of the semiconductor storage device according to the present invention; 
     FIG. 8 is an illustration showing a detailed construction of a memory cell array of another embodiment of the present invention; 
     FIG. 9 is a circuit diagram showing a construction of the conventional semiconductor storage device; 
     FIG. 10 is an illustration showing the detailed construction of the memory cell array of FIG. 9; 
     FIG. 11 is a circuit diagram showing the detailed construction of the column decoder and the redundancy column decoder of FIG. 9; and 
     FIG. 12 is a timing chart showing the operation of the conventional semiconductor storage device. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The present invention will be discussed hereinafter in detail in terms of the preferred embodiment of the present invention with reference to the accompanying drawings. In the following description, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be obvious, however, to those skilled in the art that the present invention may be practiced without these specific details. In other instance, well-known structure are not shown in detail in order to avoid unnecessary obscurity of the present invention. Also, like components as those discussed in connection with the prior art with reference to FIG. 9 will be identified by the like reference numerals, and detailed discussion for such common components will be omitted in order to avoid redundant discussion and whereby to keep the disclosure simply enough to facilitate clear understanding of the invention. One embodiment illustrated in FIG. 1 will be discussed only for different points in comparison with the conventional semiconductor storage device shown in FIG.  9 . 
     Namely, one embodiment of the semiconductor storage device according to the present invention has the same construction as the conventional semiconductor storage device shown in FIG. 9 except for four redundancy judgment circuits  11  to  14 , four OR circuits  21  to  24  and a switching circuit  7 . However, as will be discussed later, structures of the column decoder  1  and the memory cell array  5  are different from the conventional semiconductor storage device. 
     In the shown embodiment, the OR circuit  21  derives an OR of the redundancy judgment signal R 1  output from the redundancy judgment circuit  11  and the redundancy judgment signal R 2  output from the redundancy judgment circuit  12 . An output of the OR circuit  21  is input to the redundancy column decoder  2 . The OR circuit  22  derives an OR of the redundancy judgment signal R 3  output from the redundancy judgment circuit  13  and the redundancy judgment signal R 4  output from the redundancy judgment circuit  14 . An output of the OR circuit  22  is input to the redundancy column decoder  3 . 
     The OR circuit  23  derives an OR of the redundancy judgment signal R 1  output from the redundancy judgment circuit  11  and the redundancy judgment signal R 3  output from the redundancy judgment circuit  13 . An output of the OR circuit  23  is input to the switching circuit  7 . The OR circuit  24  derives an OR of the redundancy judgment signal R 2  output from the redundancy judgment circuit  12  and the redundancy judgment signal R 4  output from the redundancy judgment circuit  14 . An output of the OR circuit  24  is input to the switching circuit  7 . 
     The redundancy column decoder  2  receives output of the OR circuit  21  to output the redundancy selection signal. The redundancy column decoder  3  receives output of the OR circuit  22  to output the redundancy selection signal. The switching circuit  7  are connected the OR circuits  23  and  24  and a plurality of IO lines, and is further connected to the amplifier circuit  6  by a connection bus. 
     FIG. 2 is an illustration showing the detailed construction of the memory cell array  5  of FIG.  1 . In FIG. 2, the memory cell array  5  differentiates the IO lines between the sense amplifier (SA) connected to the redundancy column selection line and the sense amplifier connected to the redundancy column selection line. Both IO lines are connected to the same switching circuit  7 . 
     FIG. 3 is a circuit diagram showing a detailed construction of the column decoder  1  and the redundancy column decoders  2  and  3  of FIG.  1 . In FIG. 3, the redundancy column decoders  2  and  3  is constructed with the buffer circuits  2   a  and  3   a  which receive outputs of the OR circuits  21  and  22 , respectively and drive one redundancy column selection line. The column decoder  1  is constructed with a plurality of AND circuits  1   a - 1  to  1   a -n respectively receiving column address. 
     On the other hand, the amplifier circuit  6  is constructed with data amplifiers (DA)  6   a  to  6   d  connected to read/write buses RWBUS 0  to RWBUS 3 , respectively. The switching circuit  7  is constructed with switches  7   a  to  7   d  connected to the OR circuits  23  and  24  and the connection buses. 
     A plurality of column addresses respectively input to a plurality of AND circuits  1   a - 1  to  1   a -n are differentiated combination of high (High)/low (Low) levels per address. It should be noted that the column decoder  1  is different from that of the prior art and does not receive OR of the redundancy judgment signal. 
     On the other hand, to the switching circuit  7 , IO lines NIO 0  to NIO 3  transmitting data of the sense amplifiers SA connected to the column selection lines and IO lines RIO 0  to RI 03  transmitting data of the sense amplifiers connected to the redundancy column selection lines, are connected. 
     In the switching circuit  7 , the switch  7   a  switches connection between the IO lines NIO 0  and RIO 0 , the switch  7   b  switches connection between the IO lines NIO 1  and RIO 1 , the switch  7   c  switches connection between the IO lines NIO 2  and RIO 2 , and the switch  7   d  switches connection between the IO line NIO 3  and RIO 3 , respectively depending upon a level of the outputs of respective OR circuits  23  and  24 . Data of connected four IO lines are transmitted to the amplifier circuit  6  via four connection buses. 
     FIG. 4 is a timing chart showing operation of one embodiment of the semiconductor storage device according to the present invention. Operation of one embodiment of the semiconductor storage device according to the present invention will be discussed with reference to FIGS. 1 to  4 . Since cycles C 2 , C 3  and C 4  shown in FIG. 4 are read command inputs, one of the column selection lines corresponding to data of the address terminal ADD is selected. The semiconductor storage device receives the read command upon Rising of the clock of the cycle  3 . If the data of the address terminal ADD is the redundancy column address preliminarily programmed in the redundancy judgment circuit  11 , the redundancy judgment signal R 1  output from the programmed redundancy judgment circuit  11  becomes selected condition (high level). Then, outputs of OR circuits  21  and  23  become high level. Accordingly, corresponding redundancy column selection line  1  is selected (high level) and the other redundancy column selection lines  2  are not selected (low level). 
     Subsequently, the semiconductor storage device receives the read command upon rising of the clock of the cycle C 4 . If the data of the address terminal ADD is the preliminarily programmed redundancy column address, the redundancy judgment signal R 2  output from the programmed redundancy judgment circuit  12  becomes selected condition (high level). Then, outputs of OR circuits  22  and  24  become high level. Accordingly, corresponding redundancy column selection line  2  is selected (high level) and the other redundancy column selection lines  1  are not selected (low level). 
     On the other hand, in the cycle C 2 , the outputs of the OR circuits  23  and  24  are both low level. In the cycle C 3 , the output of the OR circuit  23  is high level and the output of the OR circuit  24  is low level. In the cycle C 4 , the output of the OR circuit  23  is low level and the output of the OR circuit  24  is high level. Therefore, IO lines are connected As shown in FIG.  4 . 
     Namely, in the switching circuit  7 , in the cycle C 2 , the switch  7   a  selects the IO line NIO 0 , the switch  7   b  selects the IO line NIO 1 , the switch  7   c  selects the IO line NIO 2 , and the switch  7   d  selects the IO line NIO 3 . Then, data on selected four IO lines NIO 0 , NIO 1 , NIO 2  and NIO 3  are transmitted to the amplifier circuit  6  via four connection buses. 
     In the switching circuit  7 , in the cycle C 3 , the switch  7   a  selects the IO line RIO 0 , the switch  7   b  selects the IO line NIO 1 , the switch  7   c  selects the IO line RIO 2 , and the switch  7   d  selects the IO line NIO 3 . Then, data on selected four IO lines RIO 0 , NIO 1 , RIO 2  and NIO 3  are transmitted to the amplifier circuit  6  via four connection buses. 
     In the switching circuit  7 , in the cycle C 4 , the switch  7   a  selects the IO line NIO 0 , the switch  7   b  selects the IO line RIO 1 , the switch  7   c  selects the IO line NIO 2 , and the switch  7   d  selects the IO line RIO 3 . Then, data on selected four IO lines NIO 0 , RIO 1 , NIO 2  and RIO 3  are transmitted to the amplifier circuit  6  via four connection buses. 
     In the shown embodiment, double in number of the redundancy judgment circuits  11  to  14  are provided for the redundancy column selection lines. Four IO lines are divided into two sets. The redundancy judgment circuits  11  to  14  are corresponded to respective sets to perform relieving of the defective cells, probability of relieving of the defective products can be improved. 
     FIG. 5 is a circuit diagram showing a construction of another embodiment of the semiconductor storage device according to the present invention. In FIG. 5, another embodiment of the semiconductor storage device according to the present invention is provided with four redundancy judgment circuits  11  to  14  and  15  to  18  corresponding to each redundancy selection line, and the redundancy judgment circuits  11  to  18  are corresponded to four IO lines. It should be noted that like components as those discussed in connection with the foregoing first embodiment will be identified by the like reference numerals, and detailed discussion for such common components will be omitted in order to avoid redundant discussion and whereby to keep the disclosure simply enough to facilitate clear understanding of the invention. One embodiment illustrated in FIG. 1 will be discussed only for different points in comparison with the first embodiment of the semiconductor storage device shown in FIG.  1 . 
     Namely, the shown embodiment of the semiconductor storage device according to the present invention has the same construction as the former embodiment of the semiconductor storage device of the invention shown in FIG. 1 except that four redundancy judgment circuits  15  to  18  and two OR circuits  25  and  26  are added. 
     In the shown embodiment, the OR circuit  21  derives OR of the redundancy judgment signals R 1  to R 4  of the redundancy judgment circuits  11  to  14 , and the result of OR is output to the redundancy column decoder  2 . The OR circuit  22  derives OR of the redundancy judgment signals R 5  to R 8  of the redundancy judgment circuits  15  to  18 , and the result of OR is output to the redundancy column decoder  8 . 
     The OR circuit  23  derives OR of the redundancy judgment signals R 1  of the redundancy judgment circuit  11  and the redundancy judgment signal R 5  of the redundancy judgment circuit  15  to output the result of OR operation to the switching circuit  7 . The OR circuit  24  derives OR of the redundancy judgment signals R 2  of the redundancy judgment circuit  12  and the redundancy judgment signal R 6  of the redundancy judgment circuit  16  to output the result of OR operation to the switching circuit  7 . 
     The OR circuit  25  derives OR of the redundancy judgment signals R 3  of the redundancy judgment circuit  13  and the redundancy judgment signal R 7  of the redundancy judgment circuit  17  to output the result of OR operation to the switching circuit  7 . The OR circuit  26  derives OR of the redundancy judgment signals R 4  of the redundancy judgment circuit  14  and the redundancy judgment signal R 8  of the redundancy judgment circuit  18  to output the result of OR operation to the switching circuit  7 . 
     The redundancy column decoder  2  receives the output of the OR circuit  21  to output the redundancy column selection signal. The redundancy column decoder  3  receives the output of the OR circuit  22  to output the redundancy column selection signal. The switching circuit  7  is connected to the OR circuits  23  to  26  and a plurality of IO lines and is further connected to the amplifier circuit  6  via connection buses. 
     FIG. 6 is a circuit diagram showing detailed constructions of the column decoder  1  and the redundancy column decoders  2  and  3 . In FIG. 5, the redundancy column decoders  2  and  3  is constructed with buffer circuits  2   a  and  3   a  which receive outputs of the OR circuits  21  and  22 , respectively and drive one redundancy column selection line. The column decoder  1  is constructed with a plurality of AND circuits  1   a - 1  to  1   a -n receiving the column address. 
     The amplifier circuit  6  is constructed with data amplifiers DA 6   a  to DA 6   d  connected to the read/write buses RWBUS 0  to RWBUS 3 , respectively. The switching circuit  7  is constructed with switches  7   e  to  7   h  connected to the OR circuits  23  to  26  and the connection bus. 
     The column addresses to be input to a plurality of AND circuits  1   a -i to  1   a -n differentiate combination of high (High)/low (Low) per address for selecting (high level) only one column line. Different from the prior art, the column decoder  1  does not receive OR of the redundancy judgment signal. 
     To the switching circuit  7 , the IO lines NIO 0  to NIO 3  transmitting data of the sense amplifier connected to the column selection lines, and the IO lines RIO 0  to RIO 3  transmitting data of the sense amplifier connected to the redundancy column selection lines are connected. 
     In the switching circuit, the switch  7   e  switches between the IO line NIO 0  and the IO line RIO 0  depending upon the level of the output of the OR circuit  23 . The switch  7   f  switches between the IO line NIO 1  and the IO line RIO 1  depending upon the level of the output of the OR circuit  24 . The switch  7   g  switches between the IO line NIO 2  and the IO line RIO 2  depending upon the level of the output of the OR circuit  25 . The switch  7   h  switches between the IO line NIO 3  and the IO line RIO 3  depending upon the level of the output of the OR circuit  26 . Data of connected four IO lines are transmitted to the amplifier circuit  6  via the four connection buses. 
     As set forth above, the shown embodiment provides four redundancy judgment circuits  11  to  14  and  15  to  18  for each redundancy column selection line and establishes correspondence of four IO lines to respective redundancy judgment circuits  11  to  18  for relieving the defective cell. Therefore, probability of relieving of the defective product can be improved. 
     FIG. 7 is a timing chart showing operation of the foregoing another embodiment of the semiconductor storage device according to the present invention. The operation of another embodiment of the semiconductor storage device according to the present invention will be discussed with reference to FIGS. 5 to  7 . Since cycles C 2 , C 3  and C 4  shown in FIG. 4 are read command inputs, one of the column selection lines corresponding to data of the address terminal ADD is selected. 
     When data of the address terminal ADD is the redundancy column address preliminarily programmed in the redundancy judgment circuit  11  upon rising the clock of the cycle C 3 , the redundancy judgment signal R 1  output from the programmed redundancy judgment circuit  11  becomes selected condition (high level). Then, outputs of OR circuits  21  and  23  become high level. Accordingly, corresponding redundancy column selection line  2  is selected (high level) and the other redundancy column selection lines  1  are not selected (low level). 
     On the other hand, in the cycle C 2 , the outputs of the OR circuits  23  to  26  are respectively low level. In the cycle C 3 , the outputs of the OR circuits  23  to  26  are high level, low level, low level and low level. In the cycle C 4 , the outputs of the OR circuits  23  to  26  are low level, high level, low level and low level. Therefore, the IO lines are connected as shown in FIG.  7 . 
     Namely, in the switching circuit  7  during the cycle C 2 , the switch  7   e  selects the IO line RIO 0 , the switch  7   f  selects the IO line NIO 1 , the switch  7   g  selects the IO line NIO 2  and the switch  7   h  selects the IN line NIO 3 . Thus, data of the connected four IO lines RIO 0 , NIO 1 , NIO 2  and NIO 3  are transmitted to the amplifier circuit  6  via the four connection buses. 
     Namely, in the switching circuit  7  during the cycle C 3 , the switch  7   e  selects the IO line RIO 0 , the switch  7   f  selects the IO line NIO 1 , the switch  7   g  selects the IO line NIO 2  and the switch  7   h  selects the IN line NIO 3 . Thus, data of the connected four IO lines RIO 0 , NIO 1 , NIO 2  and NIO 3  are transmitted to the amplifier circuit  6  via the four connection buses. 
     Namely, in the switching circuit  7  during the cycle C 4 , he switch  7   e  selects the IO line NO 0 , the switch  7   f  selects the IO line RO 1 , the switch  7   g  selects the IO line NIO 2  and the switch  7   h  selects the IN line NIO 3 . Thus, data of the connected four IO lines NO 0 , RO 1 , NIO 2  and NIO 3  are transmitted to the amplifier circuit  6  via the four connection buses. 
     In the shown embodiment, as shown in FIG. 7, among the IO lines connected in the cycles C 3  and C 4 , only RIO 0  and RIO 1  is connected to the redundancy sensing amplifier. 
     As set forth above, the shown embodiment provides four redundancy judgment circuits  11  to  18  for each redundancy column selection line and establishes correspondence of four IO lines to respective redundancy judgment circuits  11  to  18  for relieving the defective cell. Therefore, probability of relieving of the defective product can be improved further from the foregoing first embodiment. 
     FIG. 8 is an illustration showing the detailed construction of another embodiment of the memory cell array according to the present invention. In FIG. 8, the memory cell array  5  is differentiated from one embodiment of the memory cell array  5  of FIG. 2, in that the IO line is not connected to the IO line of other plate outside of the memory cell  5 . 
     On the other hand, the IO lines are connected to the amplifier circuits  8   a  and  8   b  separately through the IO lines transmitting data of the sense amplifier SA connected to the column selection line and the IO lines transmitted data of the sense amplifier SA connected to the redundancy column selection line. Outputs of the amplifier circuits  8   a  and  8   b  are input to switching circuits  9   a  and  9   b  for switching depending upon the redundancy judgment signal. Outputs of the switching circuits  9   a  and  9   b  are directly fed to the read/write buses RWBUS 0  to RWBUS 3 . 
     In the shown embodiment, the amplifier circuits  8   a  and  8   b  and the switching circuits  9   a  and  9   b  are provided per plate. However, since the IO lines are provided per plate to reduce load to be advantageous for high speed process. 
     As set forth above, since a plurality of redundancy judgment circuits  11  to  18  are provided to permit programming of a plurality of relieving address for one redundancy column selection line, it becomes possible to relieve the column address of the defective cell can be relieved by the redundancy cell as a part of a plurality of memory cells selected by one redundancy column selection line and other redundancy cell. Thus, probability of relieving of the defective cell can be improved. 
     Although the present invention has been illustrated and described with respect to exemplary embodiments thereof, it should be understood by those skilled in the art that the foregoing and various changes, emission and additions may be made therein and thereto, without departing from the spirit and scope of the present invention. Therefore, the present invention should not be understood as limited to the specific embodiment set out above but to include all possible embodiments which can be embodied within a scope encompassed and equivalent thereof with respect to the feature set out in the appended claims.