referring to fig1 a memory device according to the present invention has a memory cell array 101 , a word driver 102 , a column selector 103 , a bit line precharge circuit 107 and a sensing circuit 104 which comprises a sense amplifier portion 104b and a sense amplifier precharge circuit 104a . the device also comprises a write data bus line region 105 , a write circuit 106 and a control circuit 108 supplied with a set of address signals add and control signals ( not shown ) and outputting a precharge control signal pc to the bit line precharge circuit 107 , a sensing control signal sc to the sensing circuit 104 , the drive control signals ax to the word driver 102 and selection control signals ys to the column selector 103 , respectively . fig2 is a circuit diagram illustrating a part of the memory device of this embodiment , wherein equivalent parts to those in fig6 are designated by reference numerals and identical symbols to omit further description thereof . according to this embodiment , p - channel mos type precharge transistors 19 , 20 are provided for precharging the data lines 17s , 18s and the input nodes 21 and 22 of the sense amplifier sa up to the power supply voltage v d , which is about 3 v , whereas the precharge transistors 5 , 6 are formed by n - channel mos type transistors for precharging the complementary data lines 17 , 18 to the voltage v d - v t , wherein the voltage v t is a threshold voltage of each n - channel transistor and about 1 . 5 v . the transistors 3 , 4 in the memory cell mc11 , the column selection transistors 7 , 8 , the transistors 9 , 10 , 13 in the sense amplifier sa and the write gate transistors wga , wgb are also formed by using n - channel transistors . the read operation of this device will be described with reference to fig3 . note that the set of address signals add designates the memory cell mc11 . the precharge control signal pc on the precharge line 14 is preliminary at high level and the bit lines 17 and 18 are precharged by the transistors 5 , 6 to v d - v t . the sensing control signal sc on the control line 16 is at low level at this time so that the complementary signal lines 17s , 18s and the input nodes 21 , 22 of the sense amplifier sa are precharged by the transistors 19 , 20 up to the power supply voltage v d . subsequently , at the beginning of a read operation , the precharge control signal pc goes to the low level to stop the precharge operation on the bit lines 17 , 18 . at the same time , the control signal sc goes to the high level so that the precharge operation for the signal lines 17s , 18s and the nodes 21 , 22 is also completed . moreover , the column selection signal ys on the control line 23 is activated to the high level according to the address signal add . the transistors 7 , 8 are thereby turned on to connect the bit line pair 17 , 18 to the data lines 17s , 18s , respectively . in this state , the precharge level of the bit lines 17 , 18 and that of the data lines 17s , 18s are different from each other , that is , the former is v d - v t and the latter is v d , respectively . however , since the transistors 7 , 8 are of an n - channel type and supplied at the gates thereof with the high level voltage of the control signal sc , which is the power supply voltage v d , charge movement from the data lines 17s , 18s to the bit lines 17 , 18 does not occur so that the respective precharging levels are maintained . subsequently , the word line 15 is activated and energized to the high level according to the address signal add so that the memory cells mc11 is connected to the bit lines 17 , 18 via the transistors 3 , 4 . the following description will be given under the condition where the memory cell mc11 stores data &# 34 ; 0 &# 34 ; so that the node n1 connected to the transistor 3 , is at the low level voltage vs and the node n2 connected to the transistor 4 is at the high level voltage v d . in this case , one end of the transfer gate transistor 4 , which is the node n2 , is at v d and the other end thereof , which is the data line 18 , is at v d - v t . accordingly , there will occur no charge movement from the node n2 to the data line 18 via the transistor 4 since the gate voltage of the transistor 4 is at the v d level and the transistor 4 has the threshold voltage v t . the precharging voltage v d - v t of the bit line 18 is thus maintained and the precharge level of the data line 18s ( the input node 22 of the sense amplifier sa ) is also maintained . in contrast , since the node n1 within the memory cell mc11 is at the ground voltage vs , the current from the bit line 17 flows to the ground line via the transfer transistor 3 and the n - channel transistor 2tn of the inverter 2 , that is , the memory cell mc11 starts to discharge the bit line 17 as well as the data line 17s through the transistor 7 . at this time , however , the data line 17s is precharged up to the v d level , the precharge voltage v d - v t of the bit line 17 is substantially maintained at the precharge voltage v d - v t until the voltage of the data line 17s ( end of the input node 21 of the sense amplifier sa ) becomes equal to the voltage level v d - v t . in other words , when the word signal wl of the word line 15 starts to rise and the inverter 2 within the memory cell mc11 draws the charge on the data line 17 , the charges on the data line 17s replenishes the bit line 17 via the transistor 7 and , therefore , only the voltage of the signal line 17s and the node 21 is decreased . the voltage of the data line 17 does not change substantially from the precharged voltage . this period is called , hereinafter , a first read period and indicated as t1 in fig3 . during this period t1 , the voltage variation dv / dt caused on the data line 17s ( the node 21 ) per unit time is determined by the stray capacitance csb of the data line 17s and the driving ability of the memory cell mc11 which is represented by the on - current in flowing through the transistors 3 and 2tn . that is , the voltage variation dv / dt is as follows : when the voltage of the signal line 17s ( the input node 21 of the sense amplifier sa ) goes down to be equal to the voltage of the data line 17 , that is the end of the period t1 , the transistor 2tn starts to discharge both the bit line 17 and the data line 17s . a second read period t2 thereby starts from this point as shown in fig3 . therefore , during the second read period , the voltage variation dv / dt of the signal line 17s ( the input node 21 of the sense amplifier sa ) per unit time is given as follows : accordingly , the voltage level of the input node 21 of the sense amplifier sa is decreased with the inclination in / csb during the period t1 from the voltage v d and with the inclination in /( cb + csb ) during the period t2 as shown in fig3 whereas the voltage level of the data line 17 is not changed during the period t1 and decreased only after the period t1 , that is during the period t2 , from the precharge voltage v d - v t with the inclination in /( cb + csb ). for the sense amplifier sa , on the other hand , it is required to supply between the input nodes 21 , 22 thereof a voltage difference above , about 0 . 5 to 1 v to make the sense amplifies sa sense and amplify the input voltage difference . the voltage of the input node 21 of the sense amplifier sa falls to the voltage v d - v t at the end of the first read period t1 , making the input voltage difference of the sense amplifier sa as large as the voltage v t . therefore , it is sufficient for the sense amplifier sa to sense the input potential difference and output the read data out from the output node nout at the time near to the end of the period t1 or , at least , immediately after the period t1 . from a theoretical point or view , with assumption that the voltage difference vsen is smaller than the voltage vt as mentioned above and the voltage variation dv / dt is constant in the read period t1 , the time tsen needed for the sense amplifier sa to sense the read data is as follows : ## equ1 ## it is apparent , in this device , that the stored data in the memory cell mc11 substantially reflects only on the voltage of the data line 17s ( the input node 21 of the sense amplifier sa ), so that the data transfer speed is substantially independent from the capacitance cb of the bit line 17 which is very large because of its length and the large number of the memory cells mc11 being connected thereto . the capacitance csb of the data line 17s is very small owing to the minute size thereof , the read operation is achieved at considerably high speed . on the other hand , in a case where the data is transferred as a voltage decrease of the data line 17 the read operation time as large as ( vsen *( csb + cb ))/ in is needed . that is , the operating speed in a read operation according to this memory device is as several tens or a hundred times as high as in case of conventional ones . moreover , since the precharging level of the input nodes 21 , 22 of the sense amplifier sa is the power supply voltage v d , there is no decline in the sensing ability of the sense amplifier sa even under the condition where the lower power supply voltage such as 2 . 5 or 2 v is provided . furthermore , since the precharging level of the bit lines 17 , 18 is the voltage v d - v t , the power consumption of the precharging operation can be reduced and there is no possibility of deterioration in the holding ability of the memory cells mc11 to store the low level voltage as a memory data , that is , the holding margin of the memory cells mc11 is highly increased . the write operation will be explained below with reference to fig4 . the precharge control signal pc on the precharge line 14 is preliminary at high level and the bit lines 17 , 18 are precharged to the voltage v d - v t . the sensing control signal sc is at low level and the data lines 17s , 18s and the input nodes 21 , 22 of the sense amplifier sa are precharged to the power supply voltage v d . subsequently , the signals pc and sc are changed to the low level and the high level , respectively , to terminate the precharge operation of the respective lines 17 , 18 , 17s and 18s . the column selection signal ys on the line 23 is then activated to the high level so that the bit lines 17 , 18 and the data lines 17s , 18s are connected to each other , respectively . in this state , as the same as the read operation , the precharge levels of the complementary data lines 17 , 18 and the signal lines 17s , 18s , which are v d - v t and v d , respectively , are maintained owing to the transistors 7 , 8 . then , the word line 15 is activated and the memory cell mc11 is thereby connected to the bit lines 17 , 18 . at the same time , the write control signal line wsw is activated to the high level , so that the true and complementary write data signals indicative of data to be written are transferred via the write data lines wba , wbb and the write control gate transistors wga , wgb to the data lines 17s , 18s . thus , one of the data lines 17s and 18s and one of the bit lines 17 and 18 are discharged to the ground voltage vs , whereas the other data line and the other bit line 17 are maintained at the precharged voltage levels v d and v d - v t , respectively . the desired data is thus written into the cell mc11 . since the signal line 17s has a very small capacitance csb as mentioned above so that the power consumption for precharging and discharging the signal line 17s is also very small . moreover , the data line 17 is precharged only up to the voltage v d - v t which is sufficient to restrain the power consumption within a small amount . that is , when the power supply voltage v d is at 3 v and the threshold voltage v t is at 1 . 5 v as mentioned above , power consumption according to this embodiment is only half as in the case where the data lines 17 , 18 are precharged to the voltage v d . turning to fig5 a memory device of another embodiment of this invention , where parts equivalent to those in fig2 are labeled with identical symbols , corresponds to a case where a memory device has a plurality of columns of complementary data line pairs 17 and 18 associated with a single pair of the data lines 17s , 18s and a sense amplifier sa . fig5 shows a circuit configuration where two columns of the data lines 17 , 18 are provided . the transistors 7 , 8 and 71 , 81 are selectively activated by a column selection signal on the lines 23 , 24 so that a desired column of complementary data line pair is selected according to the addess signal add . in this device , each complementary data line pair 17 and 18 is precharged to the voltage v d - v t by the n - channel mos transistors 5 , 6 and the signal lines 17s , 18s and the input nodes 21 , 22 of the sense amplifier sa are precharged to the voltage v d by the p - channel mos transistors 11 , 12 . this device also achieves the high speed operation even under the condition of a low power supply voltage and has small power consumption and a large holding margin . although the case of two columns is described in fig5 this invention is applicable to the case of multiple columns as described above and , moreover , although a memory device having one port is discussed , the present invention is also applicable to each port for a memory device having a plurality of input / output ports . furthermore , the circuit configuration of the device according to the invention can be improved in such a manner that the sense amplifier sa is deactivated and the data lines 17 , 18 and the signal lines 17s , 18s are precharged immediately after the first read period t1 so as to reduce the power consumption more effectively .