Abstract:
A semiconductor memory device, having a 6F2 open bit line structure, connects each bit line of a bit line pair to a respective bit line of a neighboring bit line pair for a precharge operation so that a layout size of the semiconductor memory device decreases. Plural first precharge units each precharge one bit line of a first bit line pair and one bit line of a second bit line pair in response to a bit line equalizing signal. Plural sense amplifiers each sense a data bit supplied to a respective one of the first and second bit line pairs and amplify sensed data.

Description:
FIELD OF INVENTION  
       [0001]    The present invention relates to a semiconductor memory device; and, more particularly, to a high integrated sense amplifier of which layout size can be reduced in a semiconductor memory device having an open bit line structure. 
       DESCRIPTION OF RELATED ARTS  
       [0002]    Integration and capability of a semiconductor memory device is continuously being enhanced. There are two issues that are primarily addressed: increasing the speed at which the semiconductor memory device can operate, and increasing data storage capability of the semiconductor memory device in a restricted area. 
         [0003]    As storage capacity of the semiconductor memory device increases, a larger area is required and/or higher integration. At issue for higher integration is how to make a minuter pattern in the semiconductor memory device. A fold bit line structure (generally, referred as to an 8F2 cell structure) and an open bit line structure (generally, referred as to a 6F2 cell structure) have been suggested. Generally, the 6F2 cell structure can decrease a chip size to about 25% to 30% less than the 8F2 cell structure. 
         [0004]      FIG. 1  is a schematic circuit diagram of a sense amplifying block included in a conventional semiconductor memory device. 
         [0005]    As shown, the sense amplifying block includes first and second precharge units  10  and  11 , an equalizing unit  20 , and a sense amplifier  30 . 
         [0006]    The first precharge unit  10  precharges a first bit line pair B 1  and /B 1  with a bit line precharge voltage VBLP in response to a bit line equalizing signal BLEQ. The precharge unit  10  includes two NMOS transistors T 1  and T 2 . The bit line precharge voltage VBLP is supplied through commonly coupled drains of the NMOS transistors T 1  and T 2 . The bit line equalizing signal BLEQ is input through gates of the NMOS transistors T 1  and T 2 . 
         [0007]    Similarly, the second precharge unit  11  includes two NMOS transistors T 3  and T 4  for supplying the bit line precharge voltage VBLP to a second bit line pair B 2  and /B 2  in response to the bit line equalizing signal BLEQ. 
         [0008]    The equalizing unit  20  equalizes one of the first bit line pair, e.g., B 1 , with the other of the first bit line pair, e.g., /B 1 . The equalizing unit  20  connected between the first bit line pair B 1  and /B 1  includes NMOS transistor E 1  having a gate receiving the bit line equalizing signal BLEQ. 
         [0009]    The sense amplifier  30  comprises four MOS transistors. One of two PMOS transistors P 1  and P 2  and one of two NMOS transistors N 1  and N 2  are serially connected between a first sensing power line CSP and a second sensing power line CSN, and the other PMOS transistor and the other NMOS transistor are also serially connected between the first and second sensing power lines CSP and CSN. The sensing amplifier  30  senses a difference between voltage levels supplied on the first bit line pair B 1  and /B 1  and amplifies the difference by using voltages, e.g., VDD and GND, supplied through the first and second sensing power lines CSP and CSN. 
         [0010]    As above described, the conventional sense amplifying block includes plural transistors. For reducing a size of a cell region including the conventional sense amplifying block, the semiconductor memory device, e.g., DRAM, having a 6F2 open bit line cell structure superior to an 8F2 cell structure is designed. In consideration of reducing chip size of the semiconductor memory device, a layout of the sense amplifying block is a main factor. 
         [0011]    In the conventional sense amplifying block, the first bit line pair B 1  and /B 1  is precharged by the precharge unit  10  and the equalizing unit  20 . If the conventional sense amplifying block is fabricated by the 6F2 open bit line cell structure, a first bit line B 1  and a first bit line bar /B 1  are respectively located in different mats located in opposite sides of the sense amplifier  30 ; thus, for connecting the first bit line B 1  to the first bit line bar /B 1 , one of the first bit line B 1  to the first bit line bar /B 1  should be crossed on or under the sense amplifier  30 . 
         [0012]    Generally, in a semiconductor memory device, layout of the first bit line pair B 1  and /B 1  is limited. For example, intervals between the first bit line B 1  and the first bit line bar /B 1  and between the first bit line pair B 1  and /B 1  and a second bit line pair B 2  and /B 2 , lengths of the first bit line pair B 1  and /B 1 , or spaces between transistors and among the sense amplifier  30 , the equalizing unit  20  and the precharge unit  10 , are restricted in order to reduce interference or noise. 
         [0013]    In the conventional sense amplifying block, a crossed bit line or crossed bit line bar described above can affect a layout pitch of the sense amplifying block; and, accordingly, size of the sense amplifying block cannot be further reduced due to the crossed bit line or crossed bit line bar. 
       SUMMARY OF THE INVENTION 
       [0014]    It is an object of the present invention to provide a semiconductor memory device having a 6F2 open bit line structure which connects each of a bit line pair to each of a neighboring bit line pair for a precharge operation so that a layout size of the semiconductor memory device decreases. 
         [0015]    In accordance with an aspect of the present invention, there is provided a semiconductor memory device, including plural first precharge units, each precharging one of a first bit line pair and one of a second bit line pair in response to a bit line equalizing signal and plural sense amplifiers, each sensing a data bit supplied to one of the first and second bit line pairs and amplifying a sensed data bit. 
         [0016]    In accordance with another aspect of the present invention, there is provided a semiconductor memory device, including a first precharge unit for precharging one of a first bit line pair and one of a second bit line pair in response to a bit line equalizing signal, a second precharge unit for precharging the other of the first bit line pair and the other of the second bit line pair in response to the bit line equalizing signal, and a sense amplifier for sensing data supplied to each of the first and second bit line pairs and amplifying sensed data. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    The above and other objects and features of the present invention will become better understood with respect to the following description of the specific embodiments given in conjunction with the accompanying drawings, in which: 
           [0018]      FIG. 1  is a schematic circuit diagram of a sense amplifying block included in a conventional semiconductor memory device; 
           [0019]      FIG. 2  is a schematic circuit diagram of a sense amplifying block included in a semiconductor memory device in accordance with the present invention; and 
           [0020]      FIG. 3  is a graph showing a simulation result for comparing current consumptions between the sense amplifying blocks shown in  FIGS. 1 and 2 . 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0021]    Hereinafter, a semiconductor memory device in accordance with specific embodiments of the present invention will be described in detail with reference to the accompanying drawings. 
         [0022]      FIG. 2  is a schematic circuit diagram of a sense amplifying block included in a semiconductor memory device in accordance with the present invention. 
         [0023]    The sense amplifying block includes first and second precharge units  100  and  110 , an equalizing unit  200 , and a sense amplifier  300 . 
         [0024]    The first precharge unit  100  precharges one of a first bit line pair B 1  and /B 1  and one of a second bit line pair B 2  and /B 2  in response to a bit line equalizing signal VBLP. The second precharge unit  110  precharges the other of the first bit line pair B 1  and /B 1  and the other of the second bit line pair B 2  and /B 2  in response to the bit line equalizing signal VBLP. Particularly, in  FIG. 2 , the first precharge unit  100  precharges a first bit line B 1  and a second bit line B 2  and the second precharge unit  110  precharges a first bit line bar /B 1  and a second bit line bar /B 2 . The first and second bit line pairs B 1 , /B 1 , B 2 , and /B 2  lie adjacent to each other. 
         [0025]    The first precharge unit  100  includes first and second NMOS transistors PA and PB for supplying a precharge voltage VBLP into each of the first bit line B 1  and the second bit line B 2  in response to the bit line equalizing signal BLEQ. The second precharge unit  110  includes third and fourth NMOS transistors PC and PD for supplying the precharge voltage VBLP into each of the first bit line bar /B 1  and the second bit line bar /B 2  in response to the bit line equalizing signal BLEQ. Herein, the precharge voltage VBLP is an internal voltage for maintaining the same voltage level of the bit line and bit line bar before and after a data access. As the precharge voltage VBLP, the semiconductor memory device can generally use a power voltage VDD, a ground voltage GND, and a half power voltage ½*VDD. 
         [0026]    The equalization unit  200  equalizes voltage levels of one and the other of the first bit line pair B 1  and /B 1  in response to the bit line equalizing signal BLEQ. The equalization unit  200  includes a fifth NMOS transistor E 2 , connected between the first bit line B 1  and the first bit line bar /B 1 , having a gate receiving the bit line equalizing signal BLEQ. 
         [0027]    The sense amplifier  300  senses data supplied to each of the first and second bit line pairs B 1 , /B 1 , B 2 , and /B 2  and amplifies sensed data. The sense amplifier  300  comprises four MOS transistors: one of two PMOS transistors P 3  and P 4  and one of two NMOS transistors N 3  and N 4  are serially connected between a first sensing power line CSP and a second sensing power line CSN, and the other PMOS transistor and the other NMOS transistor are also serially connected between the first and second sensing power lines CSP and CSN. Herein, a power voltage VDD or a high voltage having higher voltage level than the power voltage VDD is supplied through the first sensing power line CSP, and a ground voltage GND is supplied through the second sensing power line CSN. 
         [0028]    The sensing amplifier  300  senses a difference between voltage levels supplied on the first bit line pair B 1  and /B 1  and amplifies the difference by using voltages, e.g., VDD and GND, supplied through the first and second sensing power lines CSP and CSN. 
         [0029]    In the present invention having above described structure, the first bit line B 1  and the second bit line  32  are coupled for a precharge operation by the first precharge unit  100 . Likewise, the first bit line bar /B 1  and the second bit line bar /B 2  are coupled for the precharge operation by the second precharge unit  110 . 
         [0030]    When the sense amplifying block is fabricated by the 6F2 open bit line cell structure, a first bit line B 1  and a first bit line bar /B 1  are located in the same cell regions; accordingly, although the first bit line B 1  is connected to the first bit line bar /B 1 , anyone of the first bit line B 1  and the first bit line bar /B 1  is not overlapped in the sense amplifier  300  and in a pitch between a bit line and a bit line bar. Thus, as compared with the conventional sense amplifying block, layout sizes of a bit line and a bit line bar can be reduced because the bit line or the bit line bar crossed into a sense amplifier for equalizing voltage levels of the bit line and the bit line bar can be removed. Accordingly, a total layout size of the sense amplifying block is also decreased. 
         [0031]      FIG. 3  is a graph showing a simulation result for comparing current consumptions between the sense amplifying blocks shown in  FIGS. 1 and 2 . Herein, the precharge voltage VBLP is a half power voltage ½*VDD. 
         [0032]    Referring to  FIG. 3 , as compared with the conventional sense amplifying block, the sense amplifying block according to the present invention consumes similar amounts of current for the precharge operation. That is, the conventional precharge operation (i.e., the precharge voltage is supplied to the first bit line B 1  and the first bit line bar /B 1 ) is not different from the precharge operation according to the present invention (i.e., the precharge voltage is supplied to the first bit line B 1  and the second bit line B 2 ) in a view of current consumption. Accordingly, the present invention can not only reduce a layout of the sense amplifying block but also support an operation speed of the precharge operation and a voltage characteristic of the precharge voltage VBLP in the conventional sense amplifying block. 
         [0033]    Further, since the first bit line B 1  connected to the second bit line B 2  is located over a core cell array, i.e., a cell region, a resistance of the first bit line B 1  can be smaller than turn-on resistances of the first and second NMOS transistors PA and PB. Thus, the present invention does not affect a performance of the sense amplifying block and can decrease a layout size of the sense amplifying block. 
         [0034]    As above described, the present invention reduces an overlap area in a pitch between a bit line and a bit line bar to decrease a layout size of the sense amplifying block. 
         [0035]    The present application contains subject matter related to the Korean patent application No. KR 10-2005-0099156, filed in the Korean Patent Office on Oct. 20, 2005, the entire contents of which being incorporated herein by references. 
         [0036]    While the present invention has been described with respect to certain specific embodiments, it will be apparent to those skilled in the art that various changes and modifications may be made without departing from the spirit and scope of the invention as defined in the following claims.