Patent Publication Number: US-7221606-B2

Title: Semiconductor memory device for low power system comprising sense amplifier with operating voltages lower/higher than ground/voltage supply and auxiliary sense amplifier

Description:
FIELD OF INVENTION 
   The present invention relates to a semiconductor memory device; and, more particularly, to a semiconductor memory device for decreasing a power consumption under a low supply voltage. 
   DESCRIPTION OF PRIOR ART 
   Generally, a semiconductor memory device is operated under a supply voltage inputted from an external circuit or a low internal voltage generated by a voltage generator included in the semiconductor memory device. Particularly, people skilled in the art focus how to make a supply voltage supplied to the semiconductor memory device become lower if an operating speed of the semiconductor memory device is not decreased. 
     FIG. 1  is a block diagram showing a core area of a conventional semiconductor memory device. 
   As shown, the conventional semiconductor memory device includes a row address decoder  20 , a column address decoder  30 , a cell area  100  and a data input/output block  40 . 
   The cell area  100  includes a plurality of cell arrays, e.g.,  110 ,  120 ,  130  and  140  and a plurality of sense amplifying blocks, e.g.,  150  and  160 . The row address decoder  20  receives a row address and decodes the row address in order to access a data stored in the cell area  100 ; and the column address decoder  30  receives a column address and decodes the column address in order to access the data stored in the cell area  100 . The data input/output block  40  is for outputting a data stored in the cell area  100  or delivering data inputted through a data pad/pin into the dell area  100 . 
   That is, during a read operation, the data accessed in response to the row address and the column address is outputted to the data input/output block  40 . Otherwise, under a write operation, a data inputted from an external circuit is stored in an unit cell corresponding to the row address and the column address through the data input/output block  40 . 
   In detail, each cell array, e.g.,  110 , included in the cell area  100  includes a plurality of unit cells, each for storing a data; and each sense amplifying block, e.g.,  150 , is for sensing and amplifying data outputted from each cell array. 
     FIG. 2  is a block diagram depicting a detailed structure of the cell area  100  shown in  FIG. 1 . 
   As shown, a first cell array  110  includes a plurality of bit line pairs, e.g., BL and /BL, a plurality of cells, e.g., CELL 1 , CELL 2  and CELL 3 , and a plurality of word lines, e.g., WL 0  to WL 5 . Herein, each cell is constituted with one capacitor and one transistor. For instance, a first cell CELL 1  includes a first capacitor C 0  coupled to a plate line PL and a first MOS transistor M 0  having a gate coupled to a first word line WL 0 . The first MOS transistor M 0  is coupled between the first capacitor C 0  and a bit line BL for connecting or disconnecting the first capacitor C 0  to a bit line BL in response to a word line WL 0 . 
   Also, the first cell CELL 1  and a second cell CELL 2  respectively coupled to the first word line WL 0  and a second word line WL 1  and neighbored with each other are commonly connected to the bit line BL; and the bit line BL is coupled to a sense amplifier  152   a  included in the sense amplifying block  150 . 
   For reading a data stored in the first cell CELL 1 , the first word line W 0  is selected and activated; then, as a result, the first MOS transistor M 0  is turned on. The data stored in the first capacitor C 0  is delivered into the bit line BL. 
   Next, the sense amplifier  152   a  senses and amplifies the data by using a potential difference between the bit line BL receiving the data delivered through the first MOS transistor M 0  and a bit line bar /BL receiving no data outputted from any cell included in the first cell array  110 . 
   After above described sensing and amplifying operations by the sense amplifier  152   a , the amplified data is outputted through a local data bus pair LDB and LDBB to the external circuit. Herein, under the sensing and amplifying operations, the sense amplifier  152   a  determines logic levels of the bit line BL and the bit line bar /BL. Also, each logic level of the bit line BL and the bit line bar /BL is transmitted to each of a local data bus LDB and a local data bus bar LDBB. 
   That is, if the first cell CELL 1  stores a data being a logic high level “1”, i.e., the first capacitor C 0  is charged, the bit line BL has a voltage level of a supply voltage VDD and the bit line bar /BL has a voltage level of a ground GND after the sensing and amplifying operations. Otherwise, i.e., if the first cell CELL 1  stores a data being a logic low level “0”, the bit line BL has a voltage level of the ground GND and the bit line bar /BL has a voltage level of the supply voltage VDD after the sensing and amplifying operations. 
   Since an amount of charge stored in each capacitor of each cell is a little, the charge should be restored in a capacitor of each original cell after the charge is delivered into the bit line BL. After completing the restoration by using a latched data of the sense amplifier, a word line corresponding to the original cell is inactivated. 
   Herein, it is described when a data stored in the third cell CELL 3  is read. If the third cell CELL 3  stores a data being a logic high level “1”, i.e., the third capacitor C 2  is charged, the bit line bar /BL has a voltage level of a supply voltage VDD and the bit line BL has a voltage level of a ground GND after the sensing and amplifying operations. Otherwise, i.e., if the third cell CELL 3  stores a data being a logic low level “0”, the bit line bar /BL has a voltage level of the ground GND and the bit line BL has a voltage level of the supply voltage VDD after the sensing and amplifying operations. 
   Further, in the write operation, i.e., when an inputted data is stored in the cell area, a word line corresponding to inputted row and column addresses is activated and, then, a data stored in a cell coupled to the word line is sensed and amplified. After then, the amplified data is substituted with the inputted data in the sense amplifier  152   a . That is, the inputted data is latched in the sense amplifier  152   a . Next, the inputted data is stored in the cell corresponding to the activated word line. If it is completed to store the inputted data in the cell, the word line corresponding to the inputted row and column addresses is inactivated. 
     FIG. 3  is a block diagram describing a connection between each cell array and each sense amplifying block included in the cell area  100  shown in  FIG. 1 . Particularly, the conventional semiconductor memory device has a shared bit line sense amplifier structure. Herein, the shared bit line sense amplifier structure means that two neighbor cell arrays are coupled to one sense amplifying block. 
   As shown, there are a plurality of cell arrays  110 ,  130  and  180  and a plurality of sense amplifying blocks  150  and  170 . The first sense amplifying block  150  is coupled to the first cell array  110  and the second cell array  130 ; and the second sense amplifying block  170  is coupled to the second cell array  130  and the fifth cell array  180 . 
   If one cell array is coupled to one sense amplifying block, the sense amplifying block includes a plurality of sense amplifiers each corresponding to each bit line pair included in the cell array. That is, the number of the sense amplifiers included in the sense amplifying block is same to the number of bit lines included in the cell array. However, referring to  FIG. 3 , since two cell arrays hold one sense amplifying block in common under the shared bit line sense amplifier structure, the sense amplifying block has a number of sense amplifiers each corresponding to each two bit line pairs. That is, the number of the sense amplifiers included in the sense amplifying block can be decreased by half. 
   Under the shared bit line sense amplifier structure for implementing a higher integrated circuit, the sense amplifying block, e.g.,  150 , further includes a first connection block  151  and a second connection block  153 . Since the sense amplifying block is commonly coupled to two neighbor cell arrays  110  and  130 , there should be control for connecting or disconnecting the first sense amplifying block  150  to one of the two neighbor cell arrays  110  and  130 . Each of the first and the second connection blocks  151  and  153  has a plurality of switching units, e.g., transistors. The plurality of transistors, e.g., MN 1  to MN 4 , in the first connection block  151  is turned on or off based on a first connection control signal BISH 1 ; and the plurality of transistors, e.g., MN 5  to MN 8 , in the second connection block  153  is turned on or off based on a second connection control signal BISL 1 . 
   For instance, if the first connection control signal BISH 1  is activated, all transistors included in the first connection block  151  is turned on, that is, the first cell array  110  is coupled to the sense amplifier block  152  of the first sense amplifying block  150 . Otherwise, if the second connection control signal BISL 1  is activated, all transistors included in the second connection block  153  is turned on, that is, the second cell array  130  is coupled to the sense amplifier block  152  of the first sense amplifying block  150 . 
   Likewise, another sense amplifying block  170  includes a plurality of sense amplifiers and two connection blocks controlled in response to other connection control signals BISH 2  and BISL 2  for connecting or disconnecting a sense amplifier block of the sense amplifying block  170  to one of the two neighbor cell arrays  130  and  180 . 
   Moreover, each sense amplifying block, e.g.,  150 , further includes a precharge block and a data output block except for connection blocks and sense amplifiers. 
     FIG. 4  is a block diagram depicting the sense amplifying block  150  shown in  FIG. 2 . 
   As shown, the sense amplifying block  150  includes a sense amplifier  152   a , a precharge block  155   a , first and second equalization blocks  154   a  and  157   a  and a data output block  156   a.    
   The sense amplifier  152   a  receives power supply signals SAP and SAN for amplifying a potential difference between the bit line BL and the bit line bar /BL. Enabled by a precharge signal BLEQ when the sense amplifier  152   a  is not activated, the precharge block  155   a  is for precharging the bit line pair BL and /BL as a bit line precharge voltage VBLP. In response to the precharge signal BLEQ, the first equalization block  154   a  makes a voltage level of the bit line BL be same to a voltage level of the bit line bar /BL. Similar to the first equalization block  154   a , the second equalization block  157   a  is also used for making a voltage level of the bit line BL be same to a voltage level of the bit line bar /BL. Lastly, the data output block  156   a  outputs a data amplified by the sense amplifier  152   a  to the local data bus pair LDB and LDBB based on a column control signal YI generated from a column address. 
   Herein, the sense amplifying block  150  further includes two connection blocks  151   a  and  153   a  each for connecting or disconnecting the sense amplifier  152   a  to one of neighbor cell arrays respectively based on connection control signals BISH and BISL. 
     FIG. 5  is a waveform showing an operation of the conventional semiconductor memory device. Hereinafter, referring to  FIGS. 1 to 5 , the operation of the conventional semiconductor memory device is described in detail. 
   As shown, the read operation can be split into four steps: a precharge step, a read step, a sense step and a restore step. Likewise, the write operation is very similar to the read operation. However, the write operation includes a write step instead of the read step in the read operation and, more minutely, not a sensed and amplified data is not outputted but an inputted data from an external circuit is latched in the sense amplifier during the sense step. 
   Hereinafter, it is assumed that a capacitor of a cell is charged, i.e., stores a logic high data “1”. Herein, a symbol ‘SN’ means a potential level charged in the capacitor of the cell. Also, one of two connection blocks in the sense amplifying block is activated and the other is inactivated. As a result, the sense amplifying block is coupled to one of two neighbor cell arrays. 
   In the precharge step, the bit line BL and the bit line bar /BL are precharged by the bit line precharge voltage VBLP. At this time, all word line are inactivated. Generally, the bit line precharge voltage VBLP is a ½ core voltage, i.e., ½ Vcore=VBLP. 
   When the precharge signal BLEQ is activated as a logic high level, the first and second equalization blocks  154   a  and  157   a  are also enabled. Thus, the bit line BL and the bit line bar /BL are percharged as the ½ core voltage. Herein, the first and second connection block  151   a  and  153   a  are also activated, i.e., all transistors included in the first and second connection block  151   a  and  153   a  are turned on. 
   In the read step, a read command is inputted and carried out. Herein, if the first connection block  151   a  is coupled to the first cell array  110  and the second connection block  153   a  is coupled to the second cell array  130 , the sense amplifier  152   a  is coupled to the first cell array  110  when the first connection block  151   a  is activated and the second connection block  153   a  is inactivated. Otherwise, when the second connection block  153   a  is activated and the first connection block  151   a  is inactivated, the sense amplifier  152   a  is coupled to the second cell array  130  and disconnected to the first cell array  110 . 
   In addition, a word line corresponding to an inputted address is activated by a supply voltage VDD or a high voltage VPP until the restore step. 
   Herein, for activating the word line, the high voltage VPP is generally used because it is requested that the supply voltage VDD becomes lower and an operating speed of the semiconductor memory device becomes faster. 
   If the word line is activated, a MOS transistor of the cell corresponding to the word line is turned on; and a data stored in a capacitor of the cell is delivered into the bit line BL. 
   Thus, the bit line BL precharged by the ½ core voltage is boosted up by a predetermined voltage level ΔV. Herein, though the capacitor is charged as the core voltage Vcore, a voltage level of the bit line BL cannot be increased to the core voltage Vcore because a capacitance Cc of the capacitor is smaller than a worm capacitance Cb of the bit line BL. 
   Referring to  FIG. 5 , in the read step, it is understood that a voltage level of the bit line BL is increased by the predetermined voltage level ΔV and the symbol ‘SN’ is also decreased to that voltage level. 
   At this time, i.e., when the data is delivered into the bit line BL, no data is delivered into the bit line bar /BL and, then, the bit line bar /BL keeps a ½ core voltage level. 
   Next, in the sense step, the first power supply signal SAP is supplied with the core voltage Vcore and the second power supply signal SAN is supplied with a ground GND. Then, the sense amplifier can amplify a voltage difference, i.e., a potential difference, between the bit line BL and the bit line bar /BL by using the first and the second power supply signals SAP and SAN. At this time, a relatively high side between the bit line BL and the bit line bar /BL is amplified to the core voltage Vcore; and the other side, i.e., a relatively low side between the bit line BL and the bit line bar /BL, is amplified to the ground GND. 
   Herein, a voltage level of the bit line BL is higher than that of the bit line bar /BL. That is, after the bit line BL and the bit line bar /BL are amplified, the bit line BL is supplied with the core voltage Vcore and the bit line bar /BL is supplied with the ground GND. 
   Lastly, in the restore step, the data outputted from the capacitor during the read step for boosting up the bit line BL by the predetermined voltage level ΔV is restored in the original capacitor. That is, the capacitor is re-charged. After the restore step, the word line corresponding to the capacitor is inactivated. 
   Then, the conventional semiconductor memory device carries out the precharge step again. Namely, the first and the second power supply signals SAP and SAN are respectively supplied with ½ core voltage Vcore. Also, the precharge signal BLEQ is activated and inputted to the first and the second equalization blocks  154   a  and  157   a  and the precharge block  155   a . At this time, the sense amplifier  152   a  is coupled to the two neighbor cell arrays, e.g.,  110  and  130 , by the first and the second connection blocks  151   a  and  153   a.    
   As a design technology for a semiconductor memory device is rapidly developed, a voltage level of a supply voltage for operating the semiconductor memory device becomes lower. However, though the voltage level of the supply voltage becomes lower, it is requested that an operation speed of the semiconductor memory device becomes faster. 
   For achieving the request about the operation speed of the semiconductor memory device, the semiconductor memory device includes an internal voltage generator for generating a core voltage Vcore having a lower voltage level than the supply voltage VDD and a high voltage VPP having a higher voltage level than the core voltage Vcore. 
   Until now, a requested operation speed can be achieved by implementing a nano-scale technology for manufacturing the semiconductor memory device through using above described manner for overcoming a decrease of the voltage level of the supply voltage VDD without any other particular method. 
   For example, through a voltage level of the supply voltage is decreased from about 3.3 V to about 2.5 V or under 2.5 V, the requested operation speed is achieved if the nano-scale technology is implemented based on from about 500 nm to about 100 nm. This means that the semiconductor memory device is more integrated. That is, as the nano-scale technology is upgraded, i.e., developed, a power consumption of a fabricated transistor included in the semiconductor memory device is reduced and, if the voltage level of the supply voltage is not decreased, an operation speed of the fabricated transistor becomes faster. 
   However, on the nano-technology based on under 100 nm, it is very difficult to develop the nano-technology. That is, there is a limitation for integrating the semiconductor memory device more and more. 
   Also, a requested voltage level of the supply voltage becomes lower, e.g., from about 2.0 V to about 1.5 V or so far as about 1.0 V. Thus, the request about the supply voltage cannot be achieved by only developing the nano-technology. 
   If a voltage level of the supply voltage inputted to the semiconductor memory device is lower than a predetermined voltage level, an operating margin of each transistor included in the semiconductor memory device is not sufficient; and, as a result, a requested operation speed is not satisfied and an operation reliability of the semiconductor memory device is not guaranteed. 
   Also, the sense amplifier needs more time for stably amplifying a voltage difference between the bit line BL and the bit line bar /BL because a predetermined turned-on voltage, i.e., a threshold voltage, of the transistor is remained under a low supply voltage. 
   Moreover, if a noise is generated at the bit line pair BL and /BL, each voltage level of the bit line BL and the bit line bar /BL is fluctuated, i.e., increased or decreased by a predetermined level on the ½ core voltage Vcore. That is, as the voltage level of the supply voltage becomes lower, a little noise can seriously affect the operation reliability of the semiconductor memory device. 
   Therefore, there is a limitation for decreasing a voltage level of the supply voltage under a predetermined level. 
   In addition, as the semiconductor memory device is more integrated, a size of the transistor becomes smaller and a distance between a gate of the transistor and the bit line gets near more and more. As a result, a bleed current is generated. Herein, the bleed current means a kind of leakage current between the gate of the transistor and the bit line because of a physical distance between the gate of the transistor and the bit line under a predetermined value. 
     FIG. 6  is a cross-sectional view describing an unit cell of the semiconductor memory device in order to show a cause of the bleed current. 
   As shown, the unit cell includes a substrate  10 , an device isolation layer  11 , source and drain regions  12   a  and  12   b , a gate electrode  13 , a bit line  17 , a capacitor  14  to  16  and insulation layers  18  and  19 . Herein, the symbol ‘A’ means a distance between the gate electrode  13  of the transistor and the bit line  17 . 
   As it is rapidly developed the nano-technology for manufacturing the semiconductor memory device, the distance between the gate electrode  13  of the transistor and the bit line  17 , i.e., ‘A’, becomes shorter. 
   In the precharge step, the bit line BL is supplied with the ½ core voltage and the gate electrode  13 , i.e., a word line, is supplied with the ground. 
   If the bit line  17  and the gate electrode  13  in an unit cell are electronically short since an error is occurred under a manufacturing process, a current is flown continuously during the precharge step and a power consumption is increased. In this case, the semiconductor memory device includes a plurality of additional unit cells for substituting the unit cell where the bit line and the gate electrode are short electronically. At this time, error cells is substituted with additional cells in word line basis. 
   Otherwise, if there is no error under the manufacturing process, i.e., the bit line  17  and the gate electrode  13  in an unit cell are not electronically short in any cell of the semiconductor memory device, there is no bleed current. However, if the distance between the gate electrode  13  of the transistor and the bit line  17 , i.e., ‘A’, is too short without any error under the manufacturing process, the bleed current is generated and flown. 
   Recently, how to operate a semiconductor memory device under a low power condition is very important. If above described bleed current is generated, it is not appreciate that the semiconductor memory device having the bleed current is applied to a system though the semiconductor memory device can be normally operated. 
   For reducing an amount of the bleed current, it is suggested that a resistor is added between the gate electrode of the transistor and the bit line. However, although the resistor can reduce little amount of the bleed current, this is not effective and essential for reducing and protecting a flow of the bleed current. 
   SUMMARY OF INVENTION 
   It is, therefore, an object of the present invention to provide a semiconductor device for operating in a fast speed under a low power condition and protecting a bleed current from generating to thereby reduce a power consumption. 
   In accordance with an aspect of the present invention, there is provided an apparatus included in a semiconductor memory device for precharging a bit line and a bit line bar and sensing and amplifying a data delivered to one of the bit line and the bit line bar, including: a precharge means for precharging the bit line and the bit line bar as a ground; a sense amplifying means for sensing and amplifying the data by using a low voltage having a lower voltage level than the ground and a high voltage having a higher voltage level than a supply voltage; and an auxiliary sense amplifying means coupled to the bit line and the bit line bar for controlling each voltage level of the bit line and the bit line bar. 
   In accordance with another aspect of the present invention, there is provided a method for precharging a bit line and a bit line bar and sensing and amplifying a data delivered to one of the bit line and the bit line bar in the semiconductor memory device, including the steps of: a) precharging the bit line and the bit line bar as a ground; b) sensing and amplifying the data by using a low voltage having a lower voltage level than the ground and a high voltage having a higher voltage level than a supply voltage; and c) maintaining a lower voltage level side between the bit line and the bit line bar as the ground while the data are sensed and amplified. 
   In accordance with another aspect of the present invention, there is provided a semiconductor memory device, including: a first cell array having a plurality of unit cells each for storing a data and outputting the data to one of a bit line and a bit line bar in response to inputted address and command; a precharge means for precharging the bit line and the bit line bar as a ground; a sense amplifying means for sensing and amplifying the data by using a low voltage having a lower voltage level than the ground and a high voltage having a higher voltage level than the core voltage; and an auxiliary sense amplifying means coupled to the bit line and the bit line bar for controlling each voltage level of the bit line and the bit line bar. 
   In accordance with another aspect of the present invention, there is provided a semiconductor memory device, including: a first cell array having a plurality of unit cells each for storing a data and outputting the data to one of a bit line and a bit line bar in response to inputted address and command; a first precharge block coupled to the first cell array for precharging the bit line or the bit line bar of the first cell array by using a ground; a second cell array having a plurality of unit cells each for storing a data and outputting the data to one of a bit line and a bit line bar in response to the inputted address and command; a second precharge block coupled to the second cell array for precharging the bit line or the bit line bar of the first cell array by using a ground; a sense amplifying block for sensing and amplifying the data outputted from one of the first and the second cell arrays by using a high voltage and a low voltage; an auxiliary sense amplifying means coupled to the bit line and the bit line bar for controlling each voltage level of the bit line and the bit line bar; a first connection control block located between the sense amplifying block and the first precharge block for connecting or disconnecting the sense amplifying block to the first precharge block; and a second connection control block located between the sense amplifying block and the first precharge block for connecting or disconnecting the sense amplifying block to the second precharge block. 

   
     BRIEF DESCRIPTION OF DRAWINGS 
     The above and other objects and features of the present invention will become apparent from the following description of preferred embodiments taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a block diagram showing a core area of a conventional semiconductor memory device; 
       FIG. 2  is a block diagram depicting a detailed structure of the cell area shown in  FIG. 1 ; 
       FIG. 3  is a block diagram describing a connection between each cell array and each sense amplifying block included in the cell area shown in  FIG. 1 ; 
       FIG. 4  is a block diagram depicting the sense amplifying block  150  shown in  FIG. 2 ; 
       FIG. 5  is a waveform showing an operation of the conventional semiconductor memory device; 
       FIG. 6  is a cross-sectional view describing an unit cell of the semiconductor memory device in order to show a cause of the bleed current; 
       FIG. 7  is a block diagram showing a core area of a semiconductor memory device in accordance with an embodiment of the present invention; 
       FIG. 8  is a first block diagram describing a sense amplifying block shown in  FIG. 7 ; 
       FIGS. 9 to 11  are waveform diagrams showing operations of the semiconductor memory device shown in  FIG. 7 ; 
       FIG. 12  is a second block diagram describing the sense amplifying block shown in  FIG. 7 ; 
       FIG. 13  is a block diagram showing a core area of a semiconductor memory device in accordance with another embodiment of the present invention; 
       FIG. 14  is a first block diagram minutely describing the core area of the semiconductor memory device shown in  FIG. 13 ; 
       FIG. 15  is a waveform showing an operation of the semiconductor memory device shown in  FIG. 14 ; and 
       FIG. 16  is a second block diagram minutely describing the core area of the semiconductor memory device shown in  FIG. 13 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Hereinafter, a semiconductor memory device for operating under a low power condition according to the present invention will be described in detail referring to the accompanying drawings. 
     FIG. 7  is a block diagram showing a core area of a semiconductor memory device in accordance with an embodiment of the present invention. 
   As shown, the semiconductor memory device includes a first reference cell block  400   a , a second reference cell block  400   b , a first cell array  300   a , a second cell array  300   b  and a sense amplifying block  200 . 
   Herein, each cell array, e.g.,  400   a , includes a plurality of unit cells, each for storing a data and outputting the data to one of a bit line and a bit line bar in response to inputted address and command; and the sense amplifying block  200  is for sensing and amplifying data outputted from each cell array. The first cell array  300   a  is coupled to the sense amplifying block  200  through a plurality of bit lines, e.g., BLn and BLn+1. The second cell array  300   b  is coupled to the sense amplifying block  200  through a plurality of bit line bars, e.g., /BLn and /BLn+1. 
   In detail, each unit cell included in the first and the second cell arrays  300   a  and  300   b  is constituted with one capacitor, e.g., Cap, and one transistor, e.g., TC. 
   The first and the second reference cell blocks  400   a  and  400   b  are for supplying a reference signal to the sense amplifying block  200  through the plurality of bit lines, e.g., BLn and BLn+1, and the plurality of bit line bars, e.g., /BLn and /BLn+1. 
     FIG. 8  is a first block diagram describing the sense amplifying block  200  shown in  FIG. 7 . 
   As shown, the sense amplifying block  200  includes a precharge block  220   a  and  220   b , a connection control block  230   a  and  230   b , a sense amplifier  210 , a data output block  240  and an auxiliary sense amplifier  260   a . In the semiconductor memory device shown in  FIG. 7 , two neighbor cell arrays, i.e.,  300   a  and  300   b  are coupled to one sense amplifying block  200 . 
   As shown, an unit cell included in the first cell array  300   a  is coupled to the sense amplifier  210  through a bit line BL and an unit cell included in the second cell array  300   b  is coupled to the sense amplifier  210  through a bit line bar /BL. Herein, there are a first precharge block  220   a  and a first connection control block  230   a  located between the first cell array  300   a  and the sense amplifier  210 . Likewise, there are a second precharge block  220   b  and a second connection control block  230   b  located between the second cell array  300   b  and the sense amplifier  210 . 
   The sense amplifier  210  receives a first power supply signal SAP and a second power supply signal SAN for amplifying a potential difference, i.e., a voltage difference, between the bit line BL and the bit line bar /BL. When the sense amplifier  210  is activated, a high voltage VPP is inputted as the first power supply signal SAP and a low voltage VBB is inputted as the second power supply signal SAN. If the sense amplifier  210  is inactivated, a ground GND is inputted as the first and the second power supply signals SAP and SAN. 
   Herein, the high voltage VPP has a higher voltage level than a supply voltage VDD inputted from an external circuit; and the low voltage VBB has a lower voltage level than the ground GND. 
   Enabled by a precharge signal BLEQ when the sense amplifier  210  is not activated, the first and the second precharge blocks  220   a  and  220   b  are for respectively precharging the bit line BL and the bit line bar /BL as the ground GND. Lastly, the data output block  240  outputs a data amplified by the sense amplifier  210  to a local data line pair, i.e., LDB and LDBB, based on an inputted column address. 
   Namely, the precharge block  220  is for precharging the bit line BL and the bit line bar /BL as a ground GND; and the sense amplifying block  210  senses and amplifies a data by using the high voltage VPP and the low voltage VBB. That is, the high voltage VPP and the low voltage VBB is respectively inputted as the first power supply signal SAP and the second power supply signal SAN. 
   Furthermore, the sense amplifying block  210  includes the first and the second connection blocks  230   a  and  230   b , each for delivering a data loaded in the bit line or the bit line bar into the sense amplifying block and preventing the low voltage VBB from delivering into the bit line and the bit line bar respectively coupled to the cell array. 
   For example, if a data stored in the first cell array  300   a  is outputted through the bit line BL in response to an inputted command, the first connection control block  230   a  is activated. As a result, the data can be delivered to the sense amplifier  210 . And then, in order to prevent the low voltage from supplying to the bit line BL connected to the first cell array  300   a , the first connection control block  230   a  is inactivated while the sense amplifier senses and amplifiers a voltage difference between the bit line BL and the bit line bar /BL. Likewise, if a data stored in the second cell array  300   b  is outputted through the bit line bar /BL in response to an inputted command, the second connection control block  230   b  is activated. As a result, the data can be delivered to the sense amplifier  210 . And then, in order to prevent the low voltage from supplying to the bit line bar /BL connected to the second cell array  300   a , the second connection control block  230   b  is inactivated while the sense amplifier senses and amplifiers a voltage difference between the bit line BL and the bit line bar /BL. 
   That is, while the sense amplifier  210  performs the sense amplifying operation, one of a sense amplifier coupled bit line SA_BL and a sense amplifier coupled bit line bar SA_/BL is decreased to the low voltage level. Herein, the sense amplifier coupled bit line SA_BL is a bit line connected between the first connection control block  230   a  and the sense amplifier  210  and the sense amplifier coupled bit line bar SA_/BL is a bit line bar connected between the second connection control block  230   b  and the sense amplifier  210 . Under assumption that the sense amplifier coupled bit line bar SA_/BL is decreased to the low voltage level, the bit line bar /BL should not be decreased to the low voltage level. For this purpose, the second connection control block  203   b  prevents the low voltage VBB from being supplied to the bit line bar /BL, whereby the bit line bar /BL stays in the ground voltage level. 
   Furthermore, the auxiliary sense amplifier  260   a  is coupled to the bit line BL and the bit line bar /BL for one of the bit line BL and the bit line bar /BL to be more stably stay in the ground voltage level while the sense amplifier  210  performs the sense amplifying operation. That is, since the first and the second connection control blocks  230   a  and  230   b  cannot stably maintain the bit line BL and the bit line bar /BL as the ground voltage level, the auxiliary sense amplifier  260   a  is provided. 
   Moreover, in the semiconductor memory device according to the present invention, the first reference cell block  400   a  supplies a reference signal to the bit line BL when the second cell array  300   b  outputs a data to the sense amplifier  210  through the bit line bar /BL. Likewise, the second reference cell block  400   b  supplies the reference signal to the bit line bar /BL when the first cell array  300   a  outputs a data to the sense amplifier  210  through the bit line BL. 
   Each of the first and the second precharge blocks  220   a  and  220   b  includes a transistor for supplying the ground GND to the bit line BL and the bit line bar /BL as the precharge voltage in response to the precharge signal BLEQ. When a precharge operation is carried out, i.e., the precharge signal BLEQ is activated, the first and the second connection control blocks  230   a  and  230   b  are also activated in response to a control signal BI. 
   The sense amplifying block  210  includes a first and a second PMOS transistors TS 1  and TS 2  and a first and a second NMOS transistors TS 3  and TS 4 . 
   The first PMOS transistor TS 1  has a gate, a drain and a source, the gate coupled to the bit line bar /BL, the source for receiving the first power supply signal SAP and the drain coupled to the bit line BL. And, the second PMOS transistor TS 2  has a gate, a drain and a source, the gate coupled to the bit line /BL, the source for receiving the first power supply signal SAP and the drain coupled to the bit line bar /BL. 
   The first NMOS transistor TS 3  has a gate, a drain and a source, the gate coupled to the bit line bar /BL, the source for receiving the second power supply signal SAN and the drain coupled to the bit line BL; and the second NMOS transistor TS 4  has a gate, a drain and a source, the gate coupled to the bit line BL, the source for receiving the second power supply signal SAN and the drain coupled to the bit line bar /BL. 
   After amplified by the sense amplifier  210 , the data is transmitted to a local data line LDB and a local data line bar LDBB through the data output block  240 . 
   The data output block  240  is for delivering the data amplified by the sense amplifying block  210  into a local data line LDB and a local data line bar LDBB or delivering an inputted data through the local data line LDB and the local data line bar LDBB into the sense amplifying block  210 . 
   In detail, the data output block  240  includes a first and a second MOS transistors TO 1  and TO 2 . The first MOS transistor TO 1  is coupled between the bit line BL and the local data line LDB for delivering a data amplified by the sense amplifier  210  into the local data line LDB or delivering an inputted data through the local data line LDB into the sense amplifying block  210  in response to a column control signal YI based on an inputted column address. Also, the second MOS transistor TO 2  is coupled between the bit line bar /BL and the local data line bar LDBB for delivering a data amplified by the sense amplifier  210  into the local data line bar LDBB or delivering an inputted data through the local data line bar LDBB into the sense amplifying block  210  in response to the column control signal YI. 
   The auxiliary sense amplifier  260   a  includes a third MOS transistor TB 1  one end of which is connected to the bit line BL and the other end of which is connected to the ground GND; and a second MOS transistor TB 2  one end of which is connected to the bit line bar /BL and the other end of which is connected to the ground GND. Herein, a gate of the third MOS transistor TB 1  is coupled to the one end of the fourth MOS transistor TB 2  and a gate of the fourth MOS transistor TB 2  is coupled to the one end of the third MOS transistor TB 1 . 
     FIGS. 9 to 11  are waveform diagrams showing operations of the semiconductor memory device shown in  FIG. 7 . 
   Referring to  FIGS. 7 to 11 , the operations of the semiconductor memory device in accordance with the present invention are described below. 
   As above described, the read operation can be split into four steps: a precharge step t 0 , a read step t 1 , a sense step t 2  and t 3  and a restore step t 4 . Likewise, a write operation is very similar to the read operation. However, the write operation includes a write step instead of the read step in the read operation and, more minutely, not a sensed and amplified data is not outputted but an inputted data from an external circuit is latched in the sense amplifier during the sense step. Further, the sense step includes a first sense step t 2  and a second sense step t 3 . The data output block  240  is activated during the second sense step t 3  because an amplified data is not stable during the first sense step t 2 . 
   Hereinafter, it is assumed that a capacitor of a cell included in the first cell array  300   a  coupled to the bit line BL is charged, i.e., stores a logic high data “1”. 
   Particularly, the bit line BL and the bit line bar /BL in the semiconductor memory device according to the present invention are precharged as the ground GND. Also, referring to  FIG. 7 , the semiconductor memory device has an open bit line structure. 
   In the precharge step t 0 , the bit line BL and the bit line bar /BL are precharged as the ground GND instead of a bit line precharge voltage VBLP generally being a ½ core voltage, i.e., ½ Vcore=VBLP. At this time, all word lines are inactivated. Namely, if the precharge signal BLEQ activated as a logic high level is kept during the precharge step t 0 , the bit line BL and the bit line bar /BL are precharged as the ground GND. 
   In the read step ti, a read command is inputted and carried out and then a word line WL corresponding to an inputted address is activated by a supply voltage VDD or a high voltage VPP until the restore step. 
   Herein, for activating the word line, the high voltage VPP is generally used because it is requested that the supply voltage VDD becomes lower and an operating speed of the semiconductor memory device becomes faster. 
   If the word line WL is activated, a MOS transistor of the cell corresponding to the word line is turned on; and a data stored in a capacitor of the cell included in the first cell array  300   a  is delivered into the bit line BL. At this time, the precharge signal BLEQ inputted to the precharge block  220  is inactivated. 
   Meanwhile, when the first cell array  300   a  outputs the stored data to the bit line BL, the second reference cell block  400   b  coupled to the bit line bar /BL outputs the reference signal having ½ voltage level of the data stored in the capacitor of the cell to the bit line bar /BL in response to a second reference control signal REF_SEL 2 . 
   Otherwise, when the second cell array  300   b  outputs a stored data to the bit line bar /BL, the first reference cell block  400   a  coupled to the bit line BL outputs the reference signal having ½ voltage level of the data stored in the capacitor of the cell included in the second cell array  300   b  into the bit line BL in response to a first reference control signal REF_SEL 1 . 
   Referring to  FIG. 9 , in the read step, it is understood that each voltage level of the bit line BL and the bit line bar /BL is increased by each predetermined voltage level, e.g. about twice voltage level. 
   Next, in the sense step t 2  and t 3  of the sense step, the first power supply signal SAP is supplied with the high voltage VPP and the second power supply signal SAN is supplied with the low voltage VBB. 
   In the first sense step t 2 , the sense amplifier  210  can amplify a voltage difference, i.e., a potential difference, between the bit line BL and the bit line bar /BL by using the first and the second power supply signals SAP and SAN. At this time, a relatively high side between the bit line BL and the bit line bar /BL is amplified to the high voltage VPP; and the other side, i.e., a relatively low side between the bit line BL and the bit line bar /BL, is amplified to the ground GND. Then, the amplified voltage difference is latched in the sense amplifier  210 . Particularly, the sense amplifier can amplify a voltage difference faster than the conventional sense amplifier because the high voltage VPP and the low voltage VBB are used instead of the supply voltage VDD and the ground GND. 
   Herein, a voltage level of the bit line BL is higher than that of the bit line bar /BL. That is, after the bit line BL and the bit line bar /BL are amplified, the bit line BL keeps a voltage level of the high voltage VPP. However, the bit line bar /BL keeps a voltage level of the ground GND through the bit bar /BL can be temporary amplified to the low voltage VBB because the second connection control blocks  230   b  is inactivated, i.e., turned off. That is, since the bit line bar /BL is precharged as the ground GND having higher voltage level than the low voltage VBB, the bit line bar /BL in the sense amplifier  210  is not amplified to the low voltage VBB. As a result, a voltage level of the bit line BL in the first cell array  300   a  can be kept as the ground GND. 
   Herein, the first and the second connection control blocks are for preventing the low voltage VBB from delivering into the bit line bar /BL in the second cell array  300   b.    
   In addition, since a worm capacitance generated by the bit line BL in the second cell array  300   b  is relatively larger, amount of current flowing a transistor included the second connection control block  230   b  is a little. Thus, a voltage level of the bit line bar /BL in the second cell array  300   b  can kept as the ground GND during the sense step t 2  and t 3  and the restore step t 4 . 
   Likewise, in the case when the bit line BL is amplified to the low voltage VBB, the first connection control block  230   a  is inactivated in order to prevent the low voltage VBB from being delivered into the bit line BL in the first cell array  300   a.    
   If the low voltage VBB is delivered into the bit line BL or the bit line bar /BL in the first or the second cell array  300   a  or  300   b , a data sensed from the first or the second cell array  300   a  or  300   b  is destroyed, i.e., a charge loaded in the bit line BL or the bit line bar /BL is discharged. Thus, it is prevented that the low voltage VBB is transmitted to the first or the second cell array  300   a  or  300   b  through the first or the second connection control block  230   a  or  230   b.    
   That is, the low voltage VBB is used for increasing an operation speed of the sense amplifier  210  but prohibited from being transmitted to the first and the second cell arrays  300   a  and  300   b.    
   Herein, as above-mentioned, the auxiliary sense amplifier  260   a  is provided for stably maintaining the bit line BL or the bit line bar /BL as the ground voltage level. 
   That is, during the sense step, the auxiliary sense amplifier  260   a  detects a voltage difference between the bit line BL and the bit line bar /BL, then controls one of the bit line BL and the bit line bar /BL which has a lower voltage level than the other to stay in the ground voltage level. 
   In case that the sense amplifier coupled bit line bar SA_/BL is amplified to the low voltage VBB, the bit line bar /BL in the second cell array  300   b  becomes the ground voltage level. At this time, for stably maintaining the bit line bar /BL as the ground voltage level, the auxiliary sense amplifier  260   a  increases a voltage level of the bit line bar /BL if the voltage level of the bit line bar /BL is lower than the ground GND or decreases the voltage level of the bit line bar /BL if the voltage level of the bit line bar /BL is higher than the ground GND. 
   As above-mentioned, each one end of the third and the fourth MOS transistors TB 1  and TB 2  is coupled to the ground GND for supplying the ground GND to one of the bit line BL and the bit line bar /BL. 
     FIG. 10  is a waveform diagram showing the above-mentioned operations of the auxiliary sense amplifier  260   a  when the semiconductor memory device performs the read operation. As shown, the bit line bar /BL is rapidly changed to the ground GND and is stably kept as the ground GND by the auxiliary sense amplifier  260   a.    
     FIG. 11  is another waveform diagram showing the above-mentioned operations of the auxiliary sense amplifier  260   a  when the semiconductor memory device performs the write operation. As shown, the bit line BL is rapidly changed to the ground GND and is stably kept as the ground GND by the auxiliary sense amplifier  260   a.    
   Particularly, in  FIG. 11 , it is shown that the sense amplifier coupled bit line SA_BL is amplified to the high voltage level and the sense amplifier coupled bit line bar SA_/BL is amplified to the low voltage level, then the bit line BL is amplified to the low voltage level and the bit line bar /BL is amplified to the high voltage level according to a logic level of a data inputted to be written. At this time, as shown, the bit line BL is changed to the ground GND and is stably kept as the ground GND by the auxiliary sense amplifier  260   a.    
   During the second sense step t 3  after the first sense step t 2 , the sense amplifier  210  continuously receives the first and the second power supply signals SAP and SAN and, then, a voltage level of the bit line BL is stabilized as the high voltage VPP. Also, an I/O control signal Yi based on an inputted column address is activated as a logic high level. In response to the activated I/O control signal Yi, the data output block  240  delivers each voltage level, i.e., data, loaded at the bit line BL and the bit line bar /BL into the local data line LDB and the local data line bar LDBB. 
   Herein, the local data line LDB and the local data line bar LDBB are precharged with a ½ core voltage Vcore when any data is not delivered. Then, when the data is delivered into the local data line LDB and the local data line bar LDBB, a voltage level of the local data line bar LDBB is temporary decreased to the ground GND since the voltage level of the bit line bar /BL is the ground GND. 
   Lastly, in the restore step t 4 , the data outputted from the capacitor during the read step for boosting up the bit line BL by the predetermined voltage level is restored in the original capacitor. That is, the capacitor is re-charged. After the restore step t 4 , the word line WL corresponding to the capacitor is inactivated. 
   After the restore step, the ground GND is supplied to the sense amplifier  210  as the first and the second power supply signals SAP and SAN. 
   In the conventional semiconductor memory device, since the local data line LDB and the local data line bar LDBB are precharged as the supply voltage VDD or a ½ supply voltage ½ VDD when any data is transmitted through the the local data line LDB and the local data line bar LDBB, a voltage level of the bit line bar /BL amplified to the ground GND by the sense amplifier  210  is increased to a predetermined level by the data output block  240 . 
   Thus, for recovering the predetermined level of the bit line bar /BL to the ground GND, the conventional semiconductor memory device has an enough time for the restore step. Otherwise, in the restore step, a fault data can be restored in the original cell of the first or the second cell array  300   a  or  300   b . For example, when an original data is “0”, a restore data can become “1”. Therefore, in the conventional semiconductor memory device, it takes an enough time, i.e., relatively long time, to perform the restore step t 4 . 
   However, the bit line bar /BL in the sense amplifier  210  is amplified to the low voltage VBB having a lower voltage level than the ground GND in the present invention. Thus, because of the low voltage VBB, a voltage level of the bit line bar /BL is little increased if the supply voltage VDD or the half supply voltage, i.e., ½ VDD, is supplied to the bit line bar /BL in the sense amplifier  210 . 
   Therefore, in the semiconductor memory device according to the present invention, a period of the restore step t 4  can be reduced. 
   Then, the semiconductor memory device performs a precharge step t 5  again. Also, the precharge signal BLEQ is activated and inputted to the precharge block  220 . At this time, the sense amplifier  210  is coupled to the two neighbor cell arrays, i.e.,  300   a  and  300   b . As a result, the bit line BL and the bit line bar /BL are precharged as the ground GND. 
   Hereinafter, it is assumed that a capacitor of a cell included in the first cell array  300   a  coupled to the bit line BL is charged, i.e., stores a logic low data “0”. 
   Likewise, in the precharge step t 0 , the bit line BL and the bit line bar /BL are precharged as the ground GND. 
   In the read step t 1 , a read command is inputted and carried out and then a word line WL corresponding to an inputted address is activated by a supply voltage VDD or a high voltage VPP until the restore step. 
   If the word line WL is activated, a MOS transistor of the cell corresponding to the word line is turned on; and a data stored in a capacitor of the cell included in the first cell array  300   a  is delivered into the bit line BL. At this time, the precharge signal BLEQ inputted to the precharge block  220  is inactivated. However, since the data is a logic low level “0”, a voltage level of the bit line BL is not changed, i.e., maintained as the ground GND. 
   Meanwhile, when the first cell array  300   a  outputs the stored data to the bit line BL, the second reference cell block  400   b  coupled to the bit line bar /BL outputs the reference signal having ½ voltage level of the data stored in the capacitor of the cell to the bit line bar /BL in response to a second reference control signal REF_SEL 2 . 
   Next, in the first sense step t 2  of the sense step, the first power supply signal SAP is supplied with the high voltage VPP and the second power supply signal SAN is supplied with the low voltage VBB. Then, the sense amplifier  210  can amplify a voltage difference, i.e., a potential difference, between the bit line BL and the bit line bar /BL by using the first and the second power supply signals SAP and SAN, i.e., the high voltage VPP and the low voltage VBB. At this time, a relatively high side between the bit line BL and the bit line bar /BL is amplified to the high voltage VPP; and the other side, i.e., a relatively low side between the bit line BL and the bit line bar /BL, is amplified to the ground GND. 
   Herein, the first and the second connection control blocks are for preventing the low voltage VBB from delivering into the bit line BL in the first cell array  300   a . As a result, the bit line BL can keep a voltage level as the ground GND because the first connection control block  230   a  is inactivated, i.e., turned off. 
   Since other steps for sensing and amplifying a logic low data, i.e., “0”, are the same to those of a logic high data, i.e., “1”, description of those steps is omitted herein. 
   Continuously, the write operation of the semiconductor memory device according to the present invention is described. The write operation receives a write command, an address and a data from an external circuit. Then, the data is inputted to the local data line LDB and the local data line bar LDBB. In the sense step, a sensed and amplified data of the sense amplifier  210  is not outputted but the inputted data from an external circuit is latched in the sense amplifier  210 . Herein, the sense step also includes the first and the second sense steps t 2  and t 3  using the high voltage VPP and the low voltage VBB in order to increase an operation speed of the sense amplifier  210 . Then, in the second sense step t 3 , an inputted data is transmitted and latched to the sense amplifier  210  through the data output block  240  in response to the column control signal YI. 
   Next, in the restore step t 4 , the data latched in the sense amplifier  210  during the sense step is stored in the capacitor corresponding to the inputted address. 
   As above described, in the read operation and the write operation, the bit line BL and the bit line bar /BL are precharged as the ground GND and the sense amplifier  210  uses the high voltage VPP and the low voltage VBB for sensing and amplifying a data stored in a cell or latching an inputted data of the local data line and the local data line pair. 
   As a result, i.e., since the sense amplifier  210  is supplied with the high voltage VPP, the operation speed of the semiconductor memory device according to the present invention is increased, i.e., improved. Also, it can be difficult to boost up a voltage level of the bit line BL or the bit line bar /BL to a predetermined voltage level since the bit line BL and the bit line bar /BL are precharged as the ground GND; however, the sense amplifier  210  can effectively amplify the voltage level by using the high voltage VPP and the low voltage VBB. 
   Based on a ground level precharge operation as above described, advantages about the semiconductor memory device according to the present invention are expected. 
   First of all, an operation margin of the sense amplifier is improved dramatically. 
   If the bit line and the bit line bar are precharged as a ½ core voltage, the sense amplifier amplifies each voltage level of the bit line and the bit line bar to the ground or the core voltage. For instance, if the core voltage is about 1.5 V, the sense amplifier amplifies about 0.75 V, i.e., ½ core voltage, to about 0 V or about 1.5 V. Herein, the voltage level of the core voltage is in proportion with a voltage level of the supply voltage which is inputted to the semiconductor memory device from an external circuit. 
   If the core voltage is about 5 V, it is not difficult operation that about 2.5 V is increased to about 5 V or decreased to about 0 V. However, if the core voltage is about 1.5 V or under 1.5 V, it is difficult to stably operate the sense amplifier in response to a noise or an interference. That is, if a noise is occurred in the semiconductor memory device after a data is loaded to one of the bit line and the bit line bar when the bit line and the bit line bar are precharged as about 0.75 V, the sense amplifier cannot sense a voltage difference between the bit line and the bit line bar. Thus, after amplified by the sense amplifier, each voltage level of the bit line and the bit line bar can be reversed. 
   However, in the present invention, the bit line and the bit line bar are precharged as the ground. Thus, though the core voltage is about 1.5 V, the sense amplifier can amplify each voltage level of the bit line and the bit line bar to the core voltage Vcore or the ground by using a voltage difference because of reducing disadvantage of the noise. Namely, in the semiconductor memory device according to the present invention, the sense amplifier can stably sense and amplify the data under a low core voltage, i.e., when the supply voltage inputted to the semiconductor memory device is low. 
   Secondly, in the semiconductor memory device according to the present invention, a bleed current generated between a word line, i.e., a gate of a transistor in each cell, and a bit line is protected. When the bit line and the bit line bar is precharged as the ground and the word line is inactivated, any current cannot be flown because there is no voltage difference between one of the bit line and the bit line bar and the inactivated word line. Thus, a power consumption of the semiconductor memory device can be reduced. 
   Thirdly, in the semiconductor memory device according to the present invention, an operation speed is improved because the sense amplifier is operated by using the high voltage VPP and the low voltage VBB although the voltage level of the supply voltage becomes lower. 
   Fourthly, the semiconductor memory device according to the present invention can reduce the period of the restore step t 4 . In the conventional semiconductor memory device, since the local data line LDB and the local data line bar LDBB are precharged as the supply voltage VDD or a ½ supply voltage ½ VDD when any data is transmitted through the the local data line LDB and the local data line bar LDBB, a voltage level of the bit line bar /BL amplified to the ground GND by the sense amplifier  210  is increased to a predetermined level by the supply voltage VDD or the ½ supply voltage ½ VDD. However, the bit line bar /BL in the sense amplifier  210  is amplified to the low voltage VBB having a lower voltage level than the ground GND in the present invention. Thus, because of the low voltage VBB, a voltage level of the bit line bar /BL is little increased if the supply voltage VDD or the half supply voltage, i.e., ½ VDD, is supplied to the bit line bar /BL in the sense amplifier  210 . 
   Lastly, in accordance with the present invention, a data of unselected cell can be protected since the auxiliary sense amplifier  260   a  maintains the bit line BL or the bit line bar /BL as the ground GND as described above. 
     FIG. 12  is a second block diagram describing the sense amplifying block  200  shown in  FIG. 7 . 
   In comparison with the amplifying block  200  shown in  FIG. 8 , an auxiliary sense amplifier  260   b  is differently configured. That is, the auxiliary sense amplifier  260   b  includes a fifth MOS transistor TB 3  one end of which is connected to the ground and the other end of which is connected to the bit line BL; and a sixth MOS transistor TB 4  one end of which is connected to the ground GND and the other end of which is connected to the bit line bar /BL. Herein, a gate of the fifth MOS transistor TB 3  is connected to the sense amplifier coupled bit line bar SA_/BL and a gate of the sixth MOS transistor TB 4  is connected to the sense amplifier coupled bit line SA_BL. Operations of the auxiliary sense amplifier  260   b  is same to the operations of the auxiliary sense amplifier  260   a  shown in  FIG. 8 . 
     FIG. 13  is a block diagram showing a core area of a semiconductor memory device in accordance with another embodiment of the present invention. 
   As shown, the semiconductor memory device includes a first reference cell block  400   c , a second reference cell block  400   d , a first cell array  300   c , a second cell array  300   d  and a sense amplifying block  200 ′. 
   Herein, each cell array, e.g.,  400   c , includes a plurality of unit cells, each for storing a data and outputting the data to one of a bit line and a bit line bar in response to inputted address and command; and the sense amplifying block  200 ′ is for sensing and amplifying data outputted from each cell array. The first cell array  300   c  is coupled to the sense amplifying block  200 ′ through a plurality of bit line pairs, e.g., BLn and /BLn. The second cell array  300   d  is coupled to the sense amplifying block  200 ′ through a plurality of bit line pairs. 
   The first and the second reference cell blocks  400   c  and  400   d  are for supplying a reference signal to the sense amplifying block  200 ′ through the plurality of bit line pairs, e.g., BLn and /BL. 
   As compared with the semiconductor memory device shown in  FIG. 7 , each cell array of the semiconductor memory device shown in  FIG. 13  is coupled to the sense amplifying block  200 ′ through the plurality of bit line pairs. Also, a location and a connection between two neighbor unit cells are different. That is, referring to  FIG. 7 , two neighbor unit cells are commonly coupled to one word line. However, as shown in  FIG. 10 , two neighbor unit cells are commonly coupled to one plate line PL, not one word line. 
     FIG. 14  is a first block diagram minutely describing the core area of the semiconductor memory device shown in  FIG. 13 . 
   As shown, the sense amplifying block  200 ′ includes a precharge block  220 ′, a sense amplifier  210 ′, a data output block  240 ′ and an auxiliary sense amplifying block  260 ′. In the semiconductor memory device shown in  FIG. 13 , two neighbor cell arrays, i.e.,  300   c  and  300   d , are coupled to one sense amplifying block  200 ′. 
   Further, the sense amplifying block  200 ′ includes a first connection control block  250   a′  and a second connection control block  250   b′  for connecting or disconnecting one of the two neighbor cell arrays, i.e.,  300   c  and  300   d , and one of the two reference cell array, i.e.,  400   c  and  400   d , to the sense amplifier  210 ′ through the bit line BL and the bit line bar /BL. Herein, the first and second power suppliers  510  and  520  are the same to those shown in  FIG. 8 . 
   Meanwhile, the auxiliary sense amplifying block  260 ′ includes a first auxiliary sense amplifier  260   c′  and a second auxiliary sense amplifier  260   d′  for maintaining lower voltage level side between the bit line BL and the bit line bar /BL as the ground GND while the sense amplifying operation is performed. 
   The first auxiliary sense amplifier  260   c′  includes a third NMOS transistor TB 5  one end of which is coupled to the ground GND and the other end of which is coupled to the bit line BL; and a fourth NMOS transistor TB 6  one end of which is coupled to the ground GND and the other end of which is coupled to the bit line bar /BL. Herein, a gate of the third NMOS transistor TB 5  is coupled to the bit line bar /BL, and a gate of the fourth NMOS transistor TB 6  is coupled to the bit line BL. 
   As shown, if an unit cell included in the first cell array  300   c  is coupled to the sense amplifier  210 ′ through a bit line BL, i.e., a data stored in the first cell array  300   c  is outputted to the sense amplifier  210 ′, the first reference cell block  400   c  outputs a reference signal to the sense amplifier  210 ′ through a bit line bar /BL. Otherwise, if an unit cell included in the second cell array  300   d  is coupled to the sense amplifier  210 ′ through a bit line bar /BL, the second reference cell block  400   d  outputs a reference signal to the sense amplifier  210 ′ through a bit line BL. 
   That is, in the semiconductor memory device according to the present invention, the first reference cell block  400   c  supplies a reference signal to one of the bit line BL and the bit line bar /BL when the first cell array  300   c  outputs a data to the sense amplifier  210 ′ through the other of the bit line BL and the bit line bar /BL. At this time, the first connection control block  250   a′  is activated, i.e., all transistors, e.g., TBH 1 , are turned on in response to a first connection control signal BISH during the read step t 1 . In addition, during the sense step t 2  and t 3  after the read step t 1 , the first connection control block  250   a′  is inactivated for preventing a data from being destroyed. Further, the first auxiliary sense amplifier  260   c′  stably maintains one of the bit line BL and the bit line bar /BL as the ground GND. 
   Likewise, the second reference cell block  400   d  supplies the reference signal to one of the bit line BL and the bit line bar /BL when the second cell array  300   d  outputs a data to the sense amplifier  210  through the other of the bit line BL and the bit line bar /BL. At this time, the second connection control block  250   b′  are activated, i.e., all transistors, e.g., TBL 1 , are turned on in response to a second connection control signal BISL during the read step t 1 . 
   The sense amplifier  210 ′ receives the high voltage VPP as the first power supply signal SAP and the ground GND as the second power supply signal SAN for amplifying a potential difference between the bit line BL and the bit line bar /BL. Enabled by a precharge signal BLEQ when the sense amplifier  210 ′ is not activated, the precharge block  220 ′ is for precharging the bit line BL and the bit line bar /BL as the ground GND. 
   Lastly, the data output block  240 ′ outputs a data amplified by the sense amplifier  210 ′ to a local data line pair, i.e., LDB and LDBB, based on an inputted column address. 
   Herein, the precharge block  220 ′ is for precharging the bit line BL and the bit line bar /BL as a ground GND; and the sense amplifying block  210 ′ senses and amplifies a data by using the high voltage VPP having a higher voltage level than the power supply voltage VDD and the low voltage VBB having a lower voltage level than the ground GND. That is, the high voltage VPP and the low voltage VBB are respectively inputted as the first and the second power supply signals SAP and SAN. 
   The precharge block  220 ′ includes a first and a second transistors TP 1 ′ and TP 2 ′. The first transistor TP 1 ′ receives a precharge signal BLEQ and supplies the ground GND to the bit line BL as the precharge voltage in response to the precharge signal BLEQ. Also, the second transistor TP 2 ′ is for receiving the precharge signal BLEQ and supplying the ground GND to the bit line bar /BL as the precharge voltage in response to the precharge signal BLEQ. 
   The sense amplifying block  210 ′ includes a first and a second PMOS transistors TS 1 ′ and TS 2 ′ and a first and a second NMOS transistors TS 3 ′ and TS 4 ′. 
   The first PMOS transistor TS 1 ′ has a gate, a drain and a source, the gate coupled to the bit line bar /BL, the source for receiving one of the core voltage Vcore and the high voltage VPP as the power supply signal SAP and the drain coupled to the bit line BL. And, the second PMOS transistor TS 2 ′ has a gate, a drain and a source, the gate coupled to the bit line /BL, the source for receiving one of the core voltage Vcore and the high voltage VPP as the power supply signal SAP and the drain coupled to the bit line bar /BL. 
   The first NMOS transistor TS 3 ′ has a gate, a drain and a source, the gate coupled to the bit line bar /BL, the source for receiving the ground GND and the drain coupled to the bit line BL; and the second NMOS transistor TS 4 ′ has a gate, a drain and a source, the gate coupled to the bit line BL, the source for receiving the ground GND and the drain coupled to the bit line bar /BL. 
   After amplified by the sense amplifier  210 ′, the data is transmitted to a local data line LDB and a local data line bar LDBB through the data output block  240 ′. 
   The data output block  240 ′ is for delivering the data amplified by the sense amplifying block  210 ′ into a local data line LDB and a local data line bar LDBB or delivering an inputted data through the local data line LDB and the local data line bar LDBB into the sense amplifying block  210 ′. 
   In detail, the data output block  240 ′ includes a first and a second MOS transistors TO 1 ′ and TO 2 ′. The first MOS transistor TO 1 ′ is coupled between the bit line BL and the data line LDB for delivering a data loaded in the bit line BL and amplified by the sense amplifier  210 ′ into the local data line LDB. Also, the second MOS transistor TO 2 ′ is coupled between the bit line bar /BL and the local data line bar LDBB for delivering a data loaded in the bit line bar /BL and amplified by the sense amplifier  210 ′ into the local data line bar LDBB. 
     FIG. 15  is a waveform showing an operation of the semiconductor memory device shown in  FIG. 14 . 
   As shown, the operation of the semiconductor memory device is very similar to above described operation shown in  FIG. 9 . However, since the semiconductor memory device has a folded structure, there are the first and the second connection control signals BISH and BISL in order to connect or disconnect one of the first and the second cell arrays, i.e.,  300   c  and  300   d , to the sense amplifier  210 ′. 
   Referring to  FIG. 15 , the first connection signal BISH is activated and the second connection signal BISL is inactivated during the read step t 1 , the sense step t 2  and t 3  and the restore step t 4 . That is, it means that the first cell array  300   c  and the first reference cell block  400   c  are coupled to the sense amplifier  210 ′ and the second cell array  300   d  and the second reference cell block  400   d  are not coupled to the sense amplifier  210 ′. 
   Otherwise, if the first connection signal BISH is inactivated and the second connection signal BISL is activated, the second cell array  300   d  and the second reference cell block  400   d  are coupled to the sense amplifier  210 ′. 
   Meanwhile, the auxiliary sense amplifying block  260 ′ serves to stably maintain one of the bit line BL and the bit line bar /BL as the ground GND. 
     FIG. 16  is a second block diagram minutely describing the core area of the semiconductor memory device shown in  FIG. 13 . 
   In comparison with the core area shown in  FIG. 14 , an auxiliary sense amplifying block  260 ′ including a first auxiliary sense amplifier  260   e  and a second auxiliary sense amplifier is differently connected in the core area. 
   That is, the first auxiliary sense amplifier  260   e′  includes a fifth NMOS transistor TB 9  one end of which is coupled to the ground GND and the other end of which is coupled to the bit line BL; and a sixth NMOS transistor TB 10  one end of which is coupled to the ground GND and the other end of which is coupled to the bit line bar /BL. Herein, a gate of the fifth NMOS transistor TB 9  is coupled to the sense amplifier coupled bit line bar SA_/BL, and a gate of the sixth NMOS transistor TB 10  is coupled to the sense amplifier coupled bit line SA_BL. 
   Likewise, the second auxiliary sense amplifier  260   f′  includes a seventh NMOS transistor TB 11  one end of which is coupled to the ground GND and the other end of which is coupled to the bit line BL; and an eighth NMOS transistor TB 12  one end of which is coupled to the ground GND and the other end of which is coupled to the bit line bar /BL. Herein, a gate of the seventh NMOS transistor TB 11  is coupled to the sense amplifier coupled bit line bar SA_/BL, and a gate of the eighth NMOS transistor TB 12  is coupled to the sense amplifier coupled bit line SA_BL. 
   Operations of the first and the second auxiliary sense amplifiers  260   e′  and  260   f′  are same to those of the first and the second auxiliary sense amplifier  260   c′  and  260   d′  shown in  FIG. 14 . 
   In the present invention, a semiconductor memory device is operated in a fast speed under a low power condition, e.g., under 1.5 V, and protects a bleed current from generating to thereby reduce a power consumption. 
   Also, as compared with the case when the bit line and the bit line bar is precharged as the ½ core voltage, the operation margin of the sense amplifier can be dramatically improved, i.e., stably operated under a noise. 
   In the semiconductor memory device according to the present invention, a bleed current is eliminated because there is no voltage difference between one of the bit line and the bit line bar and the inactivated word line. Thus, the semiconductor memory device can be reduce a power consumption and a current consumption. 
   In addition, an operation speed of the sense amplifier becomes faster because the sense amplifier is operated by using the high voltage VPP having a higher voltage level than the core voltage Vcore though the voltage level of the supply voltage becomes lower. 
   Further, the semiconductor memory device according to the present invention can reduce the period of the restore step. As a result, in the semiconductor memory device according to the present invention, an operation cycle in response to the inputted command, e.g., read or write command, can become shorter. In the conventional semiconductor memory device, since the local data line LDB and the local data line bar LDBB are precharged as the supply voltage VDD or the ½ supply voltage ½ VDD when any data is transmitted through the the local data line LDB and the local data line bar LDBB, a voltage level of the bit line bar /BL amplified to the ground GND by the sense amplifier  210  is increased to a predetermined level by the supply voltage VDD or the ½ supply voltage ½ VDD. However, the bit line bar /BL in the sense amplifier  210  is amplified to the low voltage VBB having a lower voltage level than the ground GND in the present invention. Thus, because of the low voltage VBB, a voltage level of the bit line bar /BL is little increased if the supply voltage VDD or the half supply voltage, i.e., ½ VDD, is supplied to the bit line bar /BL in the sense amplifier  210 . 
   The present application contains subject matter related to Korean patent application No. 2004-87651, filed in the Korean Patent Office on Oct. 30, 2004, the entire contents of which being incorporated herein by reference. 
   While the present invention has been described with respect to the particular embodiments, it will be apparent to those skilled in the art that various changes and modification may be made without departing from the spirit and scope of the invention as defined in the following claims.