Abstract:
Disclosed are a precharge circuit employing an inactive weak precharging and equalizing scheme, a memory device including the same and a precharging method. The inactive weak precharging and equalizing scheme equalizes a non-selected bit line and complementary bit line while sensing and amplifying memory cell data delivered to a selected bit line and complementary bit line to evaluate the voltage difference between the selected bit line and complementary bit line. Then, the scheme precharges the selected bit line and complementary bit line and the non-selected bit line and complementary bit line. This does not require high precharge driving capability for inactivated bit line and complementary bit line equalized to a predetermined voltage level so that precharge current and operating current can be reduced.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     This application claims the priority of Korean Patent Application No. 2003-87251, filed on Dec. 3, 2003, in the Korean Intellectual Property Office, the contents of which are incorporated herein in their entirety by reference.  
         [0002]     1. Field of the Invention  
         [0003]     The present invention relates to a semiconductor memory device and, more particularly, to a memory device employing an inactive weak precharging and equalizing scheme and a precharging method to reduce peak current.  
         [0004]     2. Description of the Related Art  
         [0005]     The power consumption of a semiconductor memory device is determined by an operating current flowing between a power supply voltage VDD supplied from the outside and a ground voltage VSS. The operating current I produces a predetermined IR drop caused by a resistance component R of a power line through which the power supply voltage VDD is transferred, that is, a voltage drop. In addition, the operating current brings about a predetermined IR rise, i.e., a voltage rise, due to a resistance component R of a power line through which the ground voltage VSS is transferred. This voltage drop or voltage rise on the power line serves as a load when power is provided to a semiconductor memory device.  
         [0006]     One method for reducing the power load is to decrease the resistance R of the power line. Specifically, a thick power line is employed for the memory device and this power line is connected in close proximity to a power tab entering the memory device. However, this method reduces a voltage drop occurring inside the memory device but it cannot decrease a voltage drop generated when power is supplied from an external power supply to the memory device. To reduce the voltage drop generated during power supply from the external power supply to the memory device, the operating current I should be decreased.  
         [0007]     The second method for reducing the power load is to reduce the operating current I of the memory device. The operating current I corresponds to the sum of instantaneous currents of a plurality of blocks in the memory device. Peak current that causes-maximum voltage drop or voltage rise is generated during a precharge cycle of the memory device. This is because large precharge transistors designed to remove the timing loss of the precharge cycle simultaneously operate for each column. This precharge operation is described with reference to  FIG. 1 .  
         [0008]     Referring to  FIG. 1 , a memory device  100  includes a memory cell block  110 , a first precharge block  120 , a column selector  130 , a second precharge block  140 , a precharge driver  150 , a write driver  160 , and a data input/output circuit  170 . Memory cells  111 ,  112 , 113  and  114  connected to wordlines WL 0 , . . . , WLn are connected to bit lines and complementary bit lines BL 0 , /BL 0 , BLm and /BLm. The bit lines and complementary bit lines BL 0 , /BL 0 , BLm and /BLm in the memory cell block  110  are selectively connected to the input/output circuit  170  through the column selector  130  so that data of selected memory cells  111 ,  112 ,  113  and  114  is inputted and outputted through the data input/output circuit  170 .  
         [0009]     When the memory cells  111 ,  112 ,  113  and  114  are not accessed, transistors  121   a - 121   c,    122   a - 122   c  and  140   a - 140   c  in the first and second precharge blocks  120  and  140  are turned on in response to the output of the precharge driver  150  that delivers a precharge signal PRECHARGE to precharge the bit lines and complementary bit lines BL 0 , /BL 0 , BLm and /BLm. That is, the bit lines and complementary bit lines BL 0 , /BL 0 , BLm and /BLm are precharged by the first precharge block  120  located in close proximity to the memory cell block  110  and, at the same time, the bit lines and complementary bit lines BL 0 , /BL 0 , BLm and /BLm are precharged by the second precharge block  140  adjoining the data input/output circuit  170  including a sense amplifier (not shown). This rapidly precharges the bit lines and complementary bit lines BL 0 , /BL 0 , BLm and /BLm to raise sensing speed. However, this method increases the precharge current, which induces a peak current of the memory device.  
         [0010]     A method of reducing the peak current generated during the precharge operation is disclosed in U.S. Pat. No. 6,075,733. Referring to  FIG. 2 , the circuit construction of U.S. Pat. No. 6,075,733 includes a first precharge circuit  12  for precharging bit lines  16  and  18  and a second precharge circuit  14  for precharging the bit lines  16  and  18  before the first precharge circuit  12  precharges them during a memory operation. The size of transistors  22  of the first precharge circuit  12  is larger than that of transistors  20  of the second precharge circuit  14  (X&gt;Y).  
         [0011]     With this circuit construction, the bit lines  16  and  18  are precharged by the second precharge circuit  14  whose drive intensity and current are smaller than those of the first precharge circuit. Then, the bit lines  16  and  18  are finally precharged by the first precharge circuit  12  so as to reduce the peak current. However, this two-step precharging method requires a predetermined period of time for precharging the bit lines  16  and  18 .  
         [0012]     Accordingly, a precharging method capable of decreasing power consumption while reducing bit line precharge time is needed.  
       SUMMARY OF THE INVENTION  
       [0013]     The present invention provides a precharging method that weak-precharges and equalizes bit lines that are inactivated while activated bit lines are accessed.  
         [0014]     The present invention further provides a precharge circuit for executing the precharging method.  
         [0015]     The present invention further provides a memory device including a weak precharge circuit and a strong precharge circuit.  
         [0016]     According to an aspect of the present invention, there is provided a precharging method, comprising the steps of sensing and amplifying memory cell data delivered to a selected bit line and complementary bit line pair, to evaluate the voltage difference between the bit line and complementary bit line; equalizing a non-selected bit line-complementary bit line pair; and precharging the selected bit line-complementary bit line pair and the non-selected bit line-complementary bit line pair.  
         [0017]     In one embodiment, the non-selected bit line-complementary bit line pair is equalized through a PMOS transistor that is connected between the bit line and complementary bit line and responds to a column decoding signal for selecting the bit line-complementary bit line pair and a precharge signal.  
         [0018]     In one embodiment, the selected bit line-complementary bit line pair and the non-selected bit line-complementary bit line pair are precharged to a power supply voltage level through PMOS transistors connected to the power supply voltage and each of the selected bit line-complementary bit line pair and the non-selected bit line-complementary bit line pair and the gates of the PMOS transistors are connected to the precharge signal.  
         [0019]     In one embodiment, the selected bit line-complementary bit line pair and the non-selected bit line-complementary bit line pair are precharged to the power supply voltage level through first PMOS transistors connected to the power supply voltage and each of the selected bit line-complementary bit line pair and the non-selected bit line-complementary bit line pair and a second PMOS transistor connected between each bit line and its complementary bit line, and the gates of the first and second PMOS transistors are connected to the precharge signal.  
         [0020]     According to another aspect of the present invention, there is provided a precharging method, comprising the steps of precharging a read bit line and complementary read bit line connected to a sensing circuit and then canceling the precharge; transmitting data of memory cells connected to a predetermined enabled wordline to a selected bit line and complementary bit line; sensing and amplifying the memory cell data transmitted to the selected bit line and complementary bit line through the sensing circuit, to evaluate the voltage difference between the bit line and complementary bit line, and then transmitting the memory cell data to the read bit line and complementary read bit line; equalizing the memory cell data delivered to a non-selected bit line and complementary bit line through a weak equalizing transistor; and precharging the selected bit line and complementary bit line, the non-selected bit line and complementary bit line, and the read bit line and complementary read bit line in response to a precharge signal.  
         [0021]     In one embodiment, the non-selected bit line and complementary bit line are equalized through a PMOS transistor that is connected between the bit line and complementary bit line and responds to a column decoding signal for selecting the bit line and complementary bit line and a precharge signal.  
         [0022]     In one embodiment, the non-selected bit line and complementary bit line are equalized to a voltage level lower than power supply voltage.  
         [0023]     In one embodiment, the size of transistors for precharging the selected and non-selected bit lines and complementary bit lines is smaller than that of transistors for precharging the read bit line and complementary read bit line.  
         [0024]     In one embodiment, each of the selected bit line-complementary bit line pair, the non-selected bit line-complementary bit line pair and the read bit line-complementary read bit line pair is precharged to a power supply voltage level through PMOS transistors connected to the power supply voltage and each of the selected bit line-complementary bit line pair, the non-selected bit line-complementary bit line pair and the read bit line-complementary read bit line pair, the gate of each of the PMOS transistors being connected to the precharge signal.  
         [0025]     According to another aspect of the present invention, there is provided a precharge circuit, comprising a first PMOS transistor connected between a bit line and power supply voltage, the gate of the first PMOS transistor being connected to a precharge signal; a second PMOS transistor connected between a complementary bit line and the power supply voltage, the gate of the second PMOS transistor being connected to the precharge signal; and a third PMOS transistor connected between the bit line and the complementary bit line, the gate of the third PMOS transistor being connected to a weak equalizing signal that represents that the bit line and the complementary bit line have been non-selected.  
         [0026]     According to another aspect of the present invention, there is provided a precharge circuit, comprising a first PMOS transistor connected between a bit line and power supply voltage, the gate of the first PMOS transistor being connected to a precharge signal; a second PMOS transistor connected between a complementary bit line and the power supply voltage, the gate of the second PMOS transistor being connected to the precharge signal; a third PMOS transistor connected between the bit line and the complementary bit line, the gate of the third PMOS transistor being connected to the precharge signal; and a fourth PMOS transistor connected between the bit line and the complementary bit line, the gate of the fourth PMOS transistor being connected to a weak equalizing signal that represents that the bit line and the complementary bit line have been non-selected.  
         [0027]     According to another aspect of the present invention, there is provided a precharge circuit, comprising a strong precharger for precharging a bit line and complementary bit line during a precharge operation; and a weak precharger for equalizing a non-selected bit line and complementary bit line during a normal operation and precharging the bit line and complementary bit line during the precharge operation.  
         [0028]     In one embodiment, the size of transistors of the weak precharger is smaller than that of transistors of the strong precharger.  
         [0029]     In one embodiment, the strong precharger includes: a first PMOS transistor connected between the bit line and a power supply voltage, the gate of the first PMOS transistor being connected to a precharge signal; a second PMOS transistor connected between the complementary bit line and the power supply voltage, the gate of the second PMOS transistor being connected to the precharge signal; and a third PMOS transistor connected between the bit line and the complementary bit line, the gate of the third PMOS transistor being connected to the precharge signal.  
         [0030]     In one embodiment, the weak precharger includes: a first PMOS transistor connected between the bit line and power supply voltage, the gate of the first PMOS transistor being connected to the precharge signal; a second PMOS transistor connected between the complementary bit line and the power supply voltage, the gate of the second PMOS transistor being connected to the precharge signal; and a third PMOS transistor connected between the bit line and the complementary bit line, the gate of the third PMOS transistor being connected to a weak equalizing signal that represents that the bit line and the complementary bit line have been non-selected.  
         [0031]     In one embodiment, the weak precharger includes: a first PMOS transistor connected between the bit line and a power supply voltage, the gate of the first PMOS transistor being connected to the precharge signal; a second PMOS transistor connected between the complementary bit line and the power supply voltage, the gate of the second PMOS transistor being connected to the precharge signal; a third PMOS transistor connected between the bit line and the complementary bit line, the gate of the third PMOS transistor being connected to the precharge signal; and a fourth PMOS transistor connected between the bit line and the complementary bit line, the gate of the fourth PMOS transistor being connected to a weak equalizing signal that represents that the bit line and the complementary bit line have been non-selected.  
         [0032]     According to another aspect of the present invention, there is provided a memory device, comprising a memory cell block in which a plurality of memory cells are arranged; bit lines and complementary bit lines to which data of the memory cells connected to a predetermined enabled wordline is delivered; a column selector for transmitting data on a selected bit line and complementary bit line to a read bit line and complementary read bit line; a weak precharger for equalizing a non-selected bit line and complementary bit line; a sensing circuit for sensing the memory cell data that has been delivered to the read bit line and complementary read bit line; and a strong precharger for precharging the read bit line and complementary read bit line.  
         [0033]     In one embodiment, the weak precharger includes: a first PMOS transistor connected between a bit line and the power supply voltage, the gate of the first PMOS transistor being connected to a precharge signal; a second PMOS transistor connected between a complementary bit line and the power supply voltage, the gate of the second PMOS transistor being connected to the precharge signal; and a third PMOS transistor connected between the bit line and the complementary bit line, the gate of the third PMOS transistor being connected to a weak equalizing signal that represents that the bit line and the complementary bit line have been non-selected.  
         [0034]     In one embodiment, the weak precharger includes: a first PMOS transistor connected between a bit line and power supply voltage, the gate of the first PMOS transistor being connected to a precharge signal; a second PMOS transistor connected between a complementary bit line and the power supply voltage, the gate of the second PMOS transistor being connected to the precharge signal; a third PMOS transistor connected between the bit line and the complementary bit line, the gate of the third PMOS transistor being connected to the precharge signal; and a fourth PMOS transistor connected between the bit line and the complementary bit line, the gate of the fourth PMOS transistor being connected to a weak equalizing signal that represents that the bit line and the complementary bit line have been non-selected.  
         [0035]     In one embodiment, the strong precharger includes: a first PMOS transistor connected between the read bit line and power supply voltage, the gate of the first PMOS transistor being connected to a precharge signal; a second PMOS transistor connected between the complementary bit line and the power supply voltage, the gate of the second PMOS transistor being connected to the precharge signal; and a third PMOS transistor connected between the read bit line and complementary read bit line, the gate of the third PMOS transistor being connected to the precharge signal.  
         [0036]     Accordingly, inactivated bit lines and complementary bit lines are equalized through equalizing transistors while data on an activated bit line and complementary bit line is sensed and amplified to evaluate the voltage difference between the bit line and complementary bit line. This does not require high precharge driving capability for the inactivated bit line and complementary bit line equalized to a predetermined voltage level so that precharge current and operating current can be reduced. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0037]     The foregoing and other objects, features and advantages of the invention will be apparent from the more particular description of a preferred embodiment of the invention, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention.  
         [0038]      FIG. 1  is a circuit diagram of a memory device including a conventional precharge circuit.  
         [0039]      FIG. 2  is a circuit diagram of another conventional precharge circuit.  
         [0040]      FIG. 3  is a diagram illustrating a precharging method according to the present invention.  
         [0041]      FIG. 4  is a circuit diagram of a memory device including a precharge circuit according to an embodiment of the present invention.  
         [0042]      FIG. 5  is an operation timing diagram of the memory device of  FIG. 4 . 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0043]      FIG. 3  is a diagram illustrating a precharging method in accordance with an embodiment of the present invention. Referring to  FIG. 3 , the present invention is composed of a weak precharge circuit  420  and a strong precharge circuit  440 . The weak precharge circuit  420  includes a plurality of circuit blocks  420   a,    420   b,    420   c,    420   d,    420   e,  . . . ,  420   m  connected to each pair of bit lines and the strong precharge circuit  440  is composed of one circuit block connected to the weak precharge circuit  420 .  
         [0044]     When the mth pair of bit lines is selected and activated, the mth weak precharge block  420   m  is connected to the strong precharge circuit  440  to sense and amplify data of the mth pair of bit lines through a sensing circuit connected to the strong precharge circuit  440 . The first through Ith weak precharge blocks  420   a  through  420   l  connected to inactivated bit line pairs, i.e., bit line pairs other than the activated mth bit line pair, are not connected to the strong precharge circuit  440  and respectively equalize the inactivated bit line pairs. When the inactivated bit line pairs are equalized to a voltage level lower than the power supply voltage level VDD, which is a precharge voltage level, precharge driving capability is reduced during the following precharge operation so as to reduce the peak current of the memory device.  
         [0045]      FIG. 4  is a circuit diagram of a memory device including a precharge circuit according to an embodiment of the present invention. Referring to  FIG. 4 , the memory device  400  includes a memory cell block  410 , a weak precharge block  420 , a column selector  430 , a strong precharge block  440 , a precharge driver  450 , a write driver  460 , a data input/output circuit  470 , and a weak equalizing signal generator  480 . The memory device  400  is distinguished from the conventional memory device  100  shown in  FIG. 1  at least by the construction and operation of the weak precharge block  420  and weak equalizing block  480 . The other components  410 ,  430 ,  450 ,  460  and  470  are the same as those included in general memory devices and their operations are well-known to those of ordinary skill in the art. Thus, detailed descriptions of the operations of these components are omitted.  
         [0046]     The weak precharge block  420  includes weak precharge transistors  421 ,  422 ,  423  and  424  and equalizing transistors  425  and  426  connected to bit lines and complementary bit lines BL 0  and /BL 0 , . . . , BLm and /BLm. While the bit line BL 0  and complementary bit line /BL 0  are precharged according to the weak precharge transistors  421  and  423  connected to the bit line BL 0  and complementary bit line /BL 0  in this embodiment, alternatively, a transistor whose gate is connected to a precharge signal PRECHARGE can be additionally included between the bit line BL 0  and complementary bit line /BL 0  in order to precharge the bit line BL 0  and complementary bit line /BL 0 .  
         [0047]     The weak precharge transistors  421  and  422  are connected between the power supply voltage VDD and the first bit line BL 0  and the first complementary bit line /BL 0 , respectively, and their gates are connected to a precharge signal PRECHARGE transmitted through the precharge driver  450 . The weak precharge transistors  423  and  424  are connected between the power supply voltage VDD and the mth bit line BLm and the mth complementary bit line /BLm, respectively, and their gates are connected to the precharge signal PRECHARGE delivered through the precharge driver  450 .  
         [0048]     The weak equalizing transistor  425  is connected between the first bit line BL 0  and the first complementary bit line /BL 0  and its gate is connected to a first weak equalizing signal generated by the weak equalizing signal generator  480 . The weak equalizing transistor  426  is connected between the mth bit line BLm and the mth complementary bit line /BLm and its gate is connected to the mth weak equalizing signal provided by the weak equalizing signal generator  480 .  
         [0049]     The weak precharge transistors  421  and  422  precharge the first bit line BL 0  and the first complementary bit line /BL 0  to the power supply voltage level VDD in response to the precharge signal PRECHARGE. The weak precharge transistors  423  and  424  precharge the mth bit line BLm and the mth complementary bit line /BLm to the power supply voltage level VDD in response to the precharge signal PRECHARGE. Here, transistors  441 ,  442  and  443  of the strong precharge circuit  440  precharge a read bit line BL_R and a complementary read bit line BL_R to the power supply voltage level VDD in response to the precharge signal PRECHARGE.  
         [0050]     The read bit line BL_R and the complementary read bit line /BL_R are respectively connected to the bit lines and complementary bit lines BL 0 , /BL 0 , BLm and /BLm of the memory cell block  410  through transistors  431 ,  433 ,  435  and  437  of the column selector  430 . Memory cell data delivered to the read bit line and complementary read bit line is sensed and amplified through a sensing circuit (not shown) in the data input/output circuit  470 .  
         [0051]     The weak equalizing transistor  425  equalizes the first bit line BL 0  and the first complementary bit line /BL 0  to the same voltage level in response to the first weak equalizing signal W_EQ 0 . The weak equalizing transistor  426  equalizes the mth bit line BLm and the mth complementary bit line /BLm to the same voltage level in response to the mth weak equalizing signal W_EQm. When the bit lines and complementary bit lines BL 0 , /BL 0 , BLm, and /BLm are equalized, their voltage levels before equalization become a specific voltage level through the weak equalizing transistors  425  and  426 . This specific voltage level is lower than the power supply voltage level VDD. Accordingly, the bit lines and complementary bit lines BL 0 , /BL 0 , BLm, and /BLm are weakly precharged in comparison with the precharge of the power supply voltage level VDD in the strong precharge circuit  440 .  
         [0052]     The weak equalizing signal generator  480  selectively generates the weak equalizing signals W_EQ 0 , . . . , W_EQm in response to the precharge signal PRECHARGE provided by the precharge driver  450  and column decoding signals MUX 1 , MUX 2 , . . . , MUXm. The first weak equalizing signal W_EQ 0  is generated as a logic low level signal when the first column decoding signal MUX 1  is inactivated to the logic low level to turn on the weak equalizing transistor  425 . That is, the first column decoding signal MUX 1  having the logic low level de-selects the first bit line pair BL 0  and /BL 0 , which means that the inactivated first bit line pair BL 0  and /BL 0  is weakly precharged while being equalized through the weak equalizing transistor  425 .  
         [0053]     The mth weak equalizing signal W_EQm is generated as a logic low level signal when the mth column decoding signal MUXm is at the logic low level to turn on the weak equalizing transistor  426 . Accordingly, an inactivated pair of bit lines BLm and /BLm is equalized through the weak equalizing transistor  426  and weakly precharged.  
         [0054]     Also, the first through mth weak equalizing signals W_EQ 0 , . . . , W_EQm are generated as logic low level signals when the precharge signal PRECHARGE is at logic a low level to turn on the weak equalizing transistors  425  and  426 . Even the weak precharge transistors  421 ,  422 ,  423  and  424  are turned on in response to the logic low level precharge signal PRECHARGE. Accordingly, the bit lines and complementary bit lines BL 0 , /BL 0 , BLm, and /BLm are precharged to the power supply voltage level VDD. In addition, the transistors  441 ,  442  and  443  of the strong precharge circuit  440  are turned on by the logic low level precharge signal so that the read bit line pair is precharged to the power supply voltage level VDD.  
         [0055]     If the width to length (W/L) ratio of the weak precharge transistors  421 ,  422 ,  423  and  424  and weak equalizing transistors  425  and  426  is x and the width to length (W/L) ratio of the transistors  441 ,  442  and  443  of the strong precharge circuit  440  is y, the relationship of x and y is set to be x&lt;y. Specifically, the ratio of width to length of the weak precharge transistors  421 ,  422 ,  423  and  424  and weak equalizing transistors  425  and  426  is smaller than the ratio of the width to length of the transistors  441 ,  442  and  443  of the strong precharge circuit  440 . This is because, among components that cause power consumption during the bit line precharge operation, a load component corresponding to the gate capacitance of the precharge transistors causes more power consumption than a load component caused by the capacitance of the bit lines.  
         [0056]     The operation of the memory device  400  according to the weak precharging and equalizing method of the present invention is shown in  FIG. 5 . Referring to  FIG. 5 , after the precharge signal PRECHARGE is activated from a logic low level to a logic high level, the first wordline WL 0  is activated from the logic low level to the logic high level.  
         [0057]     For convenience of description, it is assumed that the first column decoding signal MUX 0  is activated to the logic high level so that data of the first memory cell  412  is transmitted to the first bit line BL 0  and the first complementary bit line /BL 0 . Here, the other column decoding signals MUX 1 , . . . , MUXm are inactivated to the logic low level. Reference numeral  400  denotes the operation waveform of the memory device of the present invention and  100  represents the operation waveform of the conventional memory device  100  shown in  FIG. 1 .  
         [0058]     The data of the memory cell  412 , which has been delivered to the selected, i.e., activated, first bit line BL 0  and first complementary bit line. /BL 0 , is transmitted to the data input/output circuit  470  through transistors  431  and  433  of the column selector  430 , and then sensed and amplified in response to a logic high level cycle of a sensing signal SENSE, to evaluate the voltage difference between the first bit line BL 0  and the first complementary bit line /BL 0 . Here, the inactivated mth bit line BLm and mth complementary bit line /BLm are provided with data of the mth memory cell  414  as the first wordline WL 0  is enabled but they maintain a nearly identical voltage level due to the weak equalizing transistor  426 .  
         [0059]     When the first bit line BL 0  and the first complementary bit line /BL 0  are deactivated in response to the logic low level of the precharge signal PRECHARGE, they are equalized to a voltage level lower than the power supply voltage VDD through the weak equalizing transistor  425 , and the first bit line and complementary bit line BL 0  and /BL 0  are precharged to the power supply voltage VDD through the weak precharge transistors  421  and  422 . In addition, the mth bit line BLm and the mth complementary bit line /BLm are precharged to the power supply voltage level VDD by the weak equalizing transistor  426  and weak precharge transistors  423  and  424 .  
         [0060]     Referring to the operation waveform  100  of the conventional memory device, the voltage difference between the first bit line BL 0  and the first complementary bit line /BL 0  is evaluated based on data of the first memory cell  112  in response to activation of the first word line and the first column decoding signal. Then, the precharge transistors  121  and  122  and equalizing transistor  125  (referring to  FIG. 1 ) are turned on in response to activation of the precharge signal PRECHARGE to precharge the first bit line BL 0  and the first complementary bit line /BL 0  to the power supply voltage level VDD. The voltage difference between the mth bit line BLm and the mth complementary bit line /BLm is evaluated according to data of the mth memory cell  114  in response to the activation of the first wordline. Subsequently, the precharge transistors  123  and  124  and equalizing transistor  126  are turned on according to the activation of the precharge signal PRECHARGE so as to precharge the mth bit line BLm and the mth complementary bit line /BLm to the power supply voltage level VDD.  
         [0061]     In the precharge operation according to the precharge signal PRECHARGE, precharge current I(precharge) depends on the voltage level of the mth bit line BLm and the mth complementary bit line /BLm that have been inactivated before the precharge operation. Precharge current I(precharge) according to the present invention in which the inactivated mth bit line BLm and mth complementary bit line /BLm are equalized to a voltage level lower than the power supply voltage VDD and then precharged to the power supply voltage level VDD is smaller than the conventional precharge current I(precharge). This is because the conventional memory device requires higher driving capability for precharging the voltage difference between the inactivate mth bit line BLm and mth complementary bit line /BLm, which has been evaluated according to the data of the mth memory cell  114 , to the power supply voltage level VDD.  
         [0062]     Since a reduction in the precharge current brings about a decrease in the entire operating current I (VDD) of the memory device  400 , the operating current waveform of the memory device  400  according to the present invention is less than the operating current waveform of the conventional memory device  100  shown in  FIG. 1 .  
         [0063]     While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it will be understood by those of ordinary skill in the art that various changes in form and details may be made therein without departing from the spirit and scope of the present invention as defined by the following claims.