Abstract:
In a semiconductor memory device, memory cells (1-1 to 1-4, 1&#39;-1, 1&#39;-2) are divided into a plurality of blocks (BK 1 , BK 2 ) in which a plurality of pairs of sense lines (S 1 , S 1 , . . . , S 4 , S 4 ) are provided. The sense lines are commonly connected to each other, i.e., the sense lines of one block (BK 1 ) are connected to the respective sense lines of the other block (BK 2 ). The sense relationship between two adjacent sense lines (S 1 , S 2 ) belonging to one block (BK 1 ) is opposite to the sense relationship between the corresponding two adjacent sense lines (S 1 , S 2 ) belonging to the other block (BK 2 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a semiconductor memory device having memory cells divided into a plurality of separate blocks. 
     2. Description of the Prior Art 
     In recent years, dynamic metal-oxide semiconductor (MOS) random access memory (RAM) devices have been enlarged to 64 kbits (precisely, 65,536 bits). Thus, as the integration density has become higher, the number of memory cells connected to one sense amplifier for the read operation has become higher and, accordingly, the load on each sense amplifier has also become higher, thus reducing the speed of the read operation. In order to reduce the load on each sense amplifier, a prior art 64 kbits MOS RAM device uses two series of sense amplifiers. That is, the memory cells, sense amplifiers, row address decoders, and the like are divided into two blocks, each with 32 kbits. 
     Further, as the integration density has become higher, the pitch in the column direction, i.e., the distance between bit lines, has also become smaller, while, column address decoders have become larger due to the increase in the number of address bits. As a result, it has become difficult to arrange one column address decoder for each bit line pair. Therefore, an arrangement has been proposed where one column address decoder is used for every two bit line pairs, four bit line pairs, or the like. In this case, two sense line pairs, four sense line pairs, or the like are provided for each block. Of course, decoders for selecting such sense line pairs are necessary, however, such decoders are separated from the block-divided elements and, accordingly, the presence of such decoders negligibly reduces the integration density. 
     In a prior art block-divided device in which one column decoder is provided for two or more bit line pairs, i.e., two or more sense line pairs are provided for each block, the arrangement of sense lines is the same in all the blocks. As a result, when a write operation is performed upon a first pair of sense lines, and simultaneously, a read operation is performed upon a second pair of sense lines adjacent to the first pair of sense lines, noise generated by the first pair of sense lines is superposed on each line of the second pair of sense lines due to the capacitance between the adjacent lines, impurity diffusion regions, and the like. As a result, the read operation from the second pair of sense lines may be incorrectly carried out. Note that a read operation carried out simultaneously with a write operation, i.e., a read operation during the write access mode, is a so-called refresh operation. Such a refresh operation is also carried out during the read access mode, and in addition, is independently carried out during a no access mode, i.e., during the refresh mode. Regardless of what mode this prior art device is in, a read operation carried out simultaneously with a write operation can result in excessive noise being applied to the sense lines and an error in the read operation. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a block-divided semiconductor memory device having two or more sense line pairs provided for each block, in which a correct read operation can be carried out simultaneously with a write operation. 
     According to the present invention, the arrangement of the sense lines for one block is different from the arrangement of the sense lines for another block. That is, a first pair with a signal line and an inverse line is adjacent to the signal and inverse lines, respectively, of a second pair in one block and the first pair&#39;s signal line is adjacent to the inverse line of the second pair, while the second pair&#39;s signal line is adjacent to the first pair&#39;s inverse line in another block. As a result, noise from the first pair of sense lines applied to each line of the second pair of sense lines is cancelled out. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more clearly understood from the description as set forth below with reference to the drawings. 
     FIG. 1, including 1A and 1B, is a block circuit diagram of a first embodiment of a block-divided semiconductor memory device according to the present invention; 
     FIGS. 2A and 2B are partial block circuit diagrams of a portion of the diagram of FIG. 1; 
     FIG. 3 including 3A and 3B, is a block circuit diagram of a second embodiment of the block-divided semiconductor memory device according to the present invention; 
     FIGS. 4A and 4B are partial block circuit diagrams of a portion of the diagram of FIG. 3; 
     FIG. 5 is a block circuit diagram of a third embodiment of the block-divided semiconductor memory device according to the present invention; 
     FIGS. 6A and 6B are partial block circuit diagrams of a portion of the diagram of FIG. 5 and 
     FIG. 7 is another block diagram of the embodiment illustrated in FIGS. 1A and 1B. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In FIG. 1, which illustrates a first embodiment of the present invention, 64 kbits of memory cells are divided into four 16 kbit memory cell arrays 1-1, 1-2, 1-3, and 1-4. A sense amplifier/column address decoder portion 2-1 is arranged between the memory cell arrays 1-1 and 1-2, and a sense amplifier/column address decoder portion 2-2 is arranged between the memory cell arrays 1-3 and 1-4. Row address decoders 3-1 through 3-4 respond to row address signals A 0  and A 0  through A 7  and A 7  to select one word line from 256 word lines (not shown) within all the memory cell arrays 1-1 through 1-4. Therefore, the memory cell arrays 1-1 and 1-2, the sense amplifier/column address decoder portion 2-1, the row address decoders 3-1 and 3-2, and the like form a first block BK 1 , while the memory cell arrays 1-3 and 1-4, the sense amplifier/column decoder portion 2-2, the row address decoders 3-3 and 3-4, and the like form a second block BK 2 . Thus, two series of sense amplifiers are provided, thereby reducing the load thereof. 
     As illustrated in FIG. 2A, the sense amplifier/column decoder portion 2-1 comprises 256 sense amplifiers SA, each provided for one bit line pair, and 128 column address decoders DEC, each provided for two bit line pairs. Similarly, as illustrated in FIG. 2B, the sense amplifier/column decoder portion 2-2 comprises 256 sense amplifiers SA each provided for one bit line pair, and 128 column address decoders DEC each provided for two bit line pairs. The column address decoders DEC respond to column address signals A 0  &#39; and A 0  &#39; through A 6  &#39; and A 6  &#39;, to select one bit line pair. 
     In addition, two pairs of sense lines S 1  and S 1 , S 2  and S 2  selected according to column address signals A 7  &#39; and A 7  &#39; are provided for each of the blocks BK 1  and BK 2 . As illustrated in FIGS. 2A and 2B, the sense line S 1  (or S 1 ) is connected via the portion 2-1 or 2-2 to bit lines BL 0 , BL 2 , . . . , and BL 254  (or bit lines BL 0 , BL 2 , . . . , and BLHD 254), while the sense line S 2  (or S 2 ) is connected via the portion 2-1 or 2-2 to bit lines BL 1 , BL 3 , . . . , and BL 255  (or bit lines BL 1 , BL 3 , . . . , and BL 255 ). 
     In order to perform a write operation and a read operation upon a memory cell via the first pair of sense lines S 1  and S 1 , a write amplifier 4-1 and a sense buffer 5-1 are provided. Similarly, in order to perform a write operation and a read operation upon a memory cell via the second pair of the sense lines S 2  and S 2 , a write amplifier 4-2 and a sense buffer 5-2 are provided. The selection of the write amplifiers 4-1 and 4-2 is carried out by a selector 6 using the column address signals A 7  &#39; and A 7  &#39;. The selection of the sense buffers 5-1 and 5-2 is carried out by a selector 7 which also uses the column address signals A 7  &#39; and A 7  &#39;. Note that reference symbol D in  designates an input data signal and D out  designates an output data signal. 
     According to the present invention, the first pair of sense lines S 1  and S 1  are arranged in the same way for each of the blocks BK 1  and BK 2 , while the arrangement of the second pair of sense lines S 2  and S 2  in the block BK 1  is different from that in the block BK 2 . 
     Therefore, in the sense line S 2 , the noise generated by the portion of sense line S 1  in block BK 1  adjacent to a portion of the sense line S 2  has a value opposite that of the noise generated by the portion of sense line S 1  in block BK 2  adjacent to the portion of sense line S 2  in block BK 2 , and these noises cancel each other. Similarly, in the sense line S 2 , the noise due to the sense line S 1  of the block BK 1  adjacent to the sense line S 2  is opposite to the noise due to the sense line S 1  of the block BK 2  adjacent to the sense line S 2 , and these noises cancel each other. Also, in the sense lines S 1  and S 1 , the noises due to the sense lines S 2  and S 2  cancel each other. 
     In FIG. 3, which illustrates a second embodiment of the present invention, four pairs of sense lines S 1  and S 1  ; S 2  and S 2  ; S 3  and S 3  ; and S 4  and S 4  are provided. In this case, as illustrated in FIGS. 4A and 4B, the portion 2&#39;-1 (or 2&#39;-2) comprises 64 column address decoders DEC each provided for four pairs of bit lines. In this case, the column address decoders DEC respond to the column address signals A 0  &#39; and A 0  &#39; through A 5  &#39; and A 5  &#39;. In addition, two more write amplifiers 4-3 and 4-4 and two more sense buffers 5-3 and 5-4 are added to FIG. 1. A selector 6&#39; responds to the column address signals A 6  &#39;, A 6  &#39;, A 7  &#39;, and A 7  &#39; to select one of the write amplifiers 4-1 through 4-4, and a selector 7&#39; also responds to the column address signals A 6  &#39;, A  6  &#39;, A 7  &#39;, and A 7  &#39; to select one of the sense buffers 5-1 through 5-4. 
     In the first block BK 1  shown in FIG. 3, the sense lines S 1 , S 2 , S 3 , S 4 , S 4 , S 3 , S 2 , and S 1  are arranged in that order, while in the second block BK 2 , the sense lines S 1 , S 2 , S 3 , S 4 , S 4 , S 3 , S 2 , S 1  are arranged in that order. Therefore, also in this case, in one sense line such as S 2 , the noise due to the sense line S 1  or S 3  in the block BK 1  which is adjacent to the sense line S 2  cancels the noise due to the sense line S 1  or S 3  in the block BK 2  which is adjacent to the sense line S 2 . 
     In FIG. 5, which illustrates a third embodiment of the present invention, folded bit lines are arranged on one side of a sense amplifier series, as illustrated in FIGS. 6A and 6B. Note that the embodiments in FIGS. 1 and 3 use opened bit lines arranged on both sides of a sense amplifier series. In FIG. 5, sense amplifiers 2S-1 and column address decoders 2C-1 correspond to the portion 2-1 shown in FIG. 1, and sense amplifiers 2S-2 and column address decoders 2C-2 correspond to the portion 2-2 shown in FIG. 1. In addition, row address decoders 3&#39;-1 correspond to the combination of the decoders 3-1 and 3-2, shown in FIG. 1, and row address decoders 3&#39;-2 correspond to the combination of the decoders 3-3 and 3-4. In this case, the arrangement of the sense lines S 1 , S 1 , S 2 , and S 2  are the same as that in FIG. 1, thereby obtaining the same effect as in the embodiment of FIG. 1. 
     Note that the present invention can be also applied to the case where memory cells are divided into four or more blocks. For example, in the case of a four-block-divided device having four pairs of sense lines S 1  and S 1  ; S 2  and S 2  ; S 3  and S 3  ; and S 4  and S 4 , the sense lines S 1 , S 2 , S 3 , S 4 , S 3 , S 4 , S 2 , and S 1  are arranged in this order for two of the blocks, and the sense lines S 1 , S 2 , S 3 , S 4 , S 4 , S 3 , S 2 , and S 1  are arranged in this order for the other two blocks. 
     As explained above, according to the present invention, the noise due to the interaction between the sense lines is reduced, thereby obtaining a correct read operation carried out simultaneously with a write operation.