Abstract:
A semiconductor device comprises a plurality of data supply circuits, output circuits for producing a plurality of data delivered from the data supply circuit and delay circuit for transferring respective data from each data supply circuit to a different output circuit with a different delay time. Each data supply circuit includes a plurality of row lines, a row decoder for selecting the row line in response to an address signal, a plurality of memory cell arrays including memory cells selectively driven by the row line and storing data, a plurality of column lines to receive data read out from the memory cell array, and a column decoder for selecting said column lines. The delay circuit prevents a plurality of data from being simultaneously outputted.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates to a semiconductor device having a plurality of output bits and, more particularly, to a semiconductor device with reduced peak current. 
     Generally, in microcomputers, the data processing speed is one of the important factors. In recent years, more speed up is required for the operations of central processing units (CPU) or memories. 
     In the microcomputer systems, the output of the semiconductor memory is coupled with the data bus. A capacitance present in the data bus is very large and in the semiconductor memory it reaches about 150 pF. In designing the semiconductor memories, time taken from the address input to the data output is determined by considering the capacitance of the data bus. That time is selected shorter as the operating speed of the semiconductor memory increases. 
     The predominantly used microcomputers are of 8 bit type. In the description to follow, the semiconductor memory of 8 bits output will be used. Assume that the output signals of 8 bits from the memory simultaneously change their logical state from &#34;0&#34; to &#34;1&#34;. Further, assume that the memory output signal rises from 0 V to 3 V for 20 nsec. Since each bit has a capacitance of 150 pF, 8 bits have 1200 pF (=150 pF×8) capacitance and such a large capacitance must be driven. The necessary current I for driving the large capacitance is given by I=CV/t=8×150×10 -12  ×3/20×10 -9  =180 mA. In this example, 180 mA flows instantaneously. The ordinary operation current of the semiconductor memory is about 100 mA to 150 mA. For this reason, when such large current of 180 mA abruptly flows, noise is induced into the power source and the ground line, resulting in deterioration of the stable operation of the memory. In the RAM (random access memory), there is a danger that the data of the RAM are destroyed by the noise. An adverse effect of the induced noise on the peripheral integrated circuit must also be taken in account. Therefore, when the above memory is used, an additional consideration is required in designing the microcomputers. 
     The necessary current as mentioned above will be described referring to the semiconductor memory shown in FIG. 1. The semiconductor memory is comprised of a row decoder 10, a plurality of memory cell arrays 14 1  to 14 n  connected through a row line 12 to the row decoder 10, a plurality of column select circuits 18 1  to 18 n  connected through a column line 16 to the memory cell arrays 14 1  to 14 n , a column decoder 20 connected to the column select circuits 18 1  to 18 n , a plurality of sense amplifiers 22 1  to 22 n  correspondingly connected to the column select circuits 18 1  to 18 n , and a plurality of output buffer circuits 24 1  to 24 n  correspondingly connected to the sense amplifiers 22 1  to 22 n . The output terminals of the output buffer circuits 24 1  to 24 n  are correspondingly connected to external output terminals, respectively. 
     In each of the memory cell arrays 14 1  to 14 n , memory cells are located at cross points of the row lines 12 and the column lines 16. A desired memory cell at the cross points is specified by one of the row lines driven by the row decoder 10 in response to a row address input signal and one column line selected respectively by the column select circuits 18 1  to 18 n  driven by the column decoder 20 in response to a column address input signal. Through the consecutive memory cell specifying operations, data are read out bit by bit from the memory cell arrays 14 1  to 14 n . In this way, the data of 8 bits are sent to the external output terminals. 
     In the semiconductor memory, to minimize the chip size, the row lines are wired using polysilicon and the output lines of the column decoder 20 are wired using aluminum. Since polysilicon has normally 30 to 50 Ω/μ 2 , a voltage on the row line remote from the row decoder 10 has a time delay with respect to that on the line near the row decoder 10. When a memory cell of each of the memory cell arrays is selected depending on a change of the row address, the memory cell near the row decoder is selected faster selected than the remote one. Accordingly, times that the data are produced from the selected memories are different depending on the locations of the selected memory cells from the row decoder 10. Therefore, the data of 8 bits are not simultaneously produced from the output buffers 24 1  to 24 n  and the above 180 mA never flows. 
     Let us consider a case where only the column address changes. The output lines from the column decoder 20 are made of aluminum, as previously stated, due to the pattern layout employed in their fabrication stage. Their resistance is about 0Ω. In selecting the column lines by the column select circuit, each of the column selects circuits select a single column line. The column line selections by the select circuits are performed simultaneously. Therefore, 8-bit data are simultaneously outputted from the selected memory cells. Then, the 180 mA current instantaneously flows at this time, possibly resulting in an erroneous operation. Thus, when the column addresses change to produce data, there is the highest possibility that noise is induced into the power source and the ground line. 
     In FIG. 2, illustrating the output buffers of CPU, the output buffers 28 1  to 28 n  connected to an internal bus 26 produce data to an external bus 30 under control of a control signal S. When the control signal S is inputted to the output buffers 28 1  to 28 n  concurrently and the buffers operate, a large instantaneous current flows to cause noise in the semiconductor device. 
     FIG. 3 illustrates another prior semiconductor memory with a plurality of bits. The column lines of memory cell arrays 14 1  to 14 n  are simultaneously precharged by a column line precharge circuit 32, in synchronism with a precharge signal PC. The contents of the memory cell selected by the row decoder 10 appear on paired column lines Q 1  and Q 1  to Q n  and Q n . A column decoder 20 drives column select circuits 18 1  to 18 n . Data on the column lines decoded by the column select circuits 18 1  to 18 n  are sensed by sense amplifiers 22 1  to 22 n . The sensed values are outputted to output terminals through output buffers 24 1  to 24 n . 
     FIG. 4 shows yet another prior semiconductor memory with a plurality of output bits. The column lines of memory cell arrays 14 1  to 14 n  are simultaneously precharged by column line precharge circuits 32 1  to 32 n  in synchronism with a precharged signal PC. The data of the memory cell selected by the row decoder 10 appear on the column lines Q 11  to Q nm . The data are sensed by corresponding sense amplifier circuits 22 1  to 22 n , respectively. The output signals from the sense amplifiers 22 1  to 22 n  are selected by column select circuits 18 1  to 18 n  and produced to output terminals 24 1  to 24 n , respectively. 
     In the prior semiconductor memories shown in FIGS. 3 and 4, a pulse width of the precharge signal PC is determined by detecting that the output signal from the row decoder 10 reaches the terminal E n  of the row line 12 (FIG. 3). Since the row lines 12 are normally made of polysilicon, those have about 30 Ω/□. The row line 12 has a relatively large load capacitance since such lines are connected to the gates of the memory cell transistors. For this reason, there is a difference between a rise time of data at a node E o  near the row decoder 10 and that at a node E n  remote from the row decoder 10. To cope with this problem, the prior art precharges the column lines until the data on the row lines reach E n  and the row lines 12 all have a &#34;1&#34; level. At an instant that the signal level on the row lines 12 becomes a &#34;1&#34; level, the precharge signal PC is stopped. 
     FIG. 5 shows an example of the precharge circuit. 
     In the semiconductor memory as mentioned above, at an instant that the precharge is stopped, the sense amplifiers 22 1  to 22 n  start to operate. The output data from the sense amplifiers are transferred to the output buffer circuits 24 1  to 24 n  of the data input/output circuit, respectively. In this way, the initial operation of the respective sense amplifiers and the outputs of data of the plurality of bits are performed concurrently. As a result, the instantaneous peak current is very large. This causes noise in the power source, like the FIG. 1 prior art. Additionally, the noise induced narrows an operating margin of the circuit in each memory. Since a large capacitance of about 150 pF is contained in the exterior circuit, as mentioned above, the instantaneous current due to the charge/discharge to and from the capacitor is considerably large. 
     SUMMARY OF THE INVENTION 
     Accordingly, an object of the present invention is to provide a semiconductor device which can prevent a plurality of data from being simultaneously outputted and can reduce instantaneous peak current. 
     To achieve the above object, a semiconductor device according to the present invention is comprised of a plurality of circuits for supplying data, a plurality of output circuits for receiving inputs from respective data supply circuits to produce data, and a delay circuit for delaying data transferred from respective output circuit. 
     With such an arrangement, data are prevented from being concurrently produced from the plurality of output circuits, so that the instantaneous peak current is small, thus suppressing generation of noise. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of this invention will be apparent from the following description taken in connection with the accompanying drawings, in which: 
     FIG. 1 is a block diagram of a prior semiconductor memory device; 
     FIG. 2 is a block diagram of an output section of a prior central processing unit; 
     FIGS. 3 and 4 are block diagrams of prior semiconductor memory devices each with a precharge circuit for the column lines; 
     FIG. 5 is a circuit diagram of the precharge circuit; 
     FIG. 6 is a block diagram of a first embodiment of a semiconductor device according to the present invention; 
     FIG. 7 is a block diagram of a second embodiment of a semiconductor device according to the present invention; 
     FIGS. 8A through 8E show some delay means applicable for the circuits shown in FIGS. 6 and 7; 
     FIG. 9 shows a circuit diagram of a third embodiment of a semiconductor device according to the present invention; 
     FIG. 10 shows a circuit diagram of a fourth embodiment of a semiconductor device according to the present invention; 
     FIG. 11 shows a circuit diagram of an output buffer circuit used in the semiconductor device shown in FIG. 10; 
     FIG. 12 shows a timing chart useful in explaining the operation of the output buffer circuit shown in FIG. 11; 
     FIG. 13 shows a block diagram of a fifth embodiment of a semiconductor device according to the present invention; 
     FIG. 14 shows potential change of respective node of the dummy column line used in the FIG. 13 circuit; 
     FIG. 15 shows a set of waveforms of precharge signals generated in the FIG. 13 circuit; 
     FIG. 16 shows a circuit diagram of an address buffer circuit used in the FIG. 13 circuit; 
     FIG. 17 is a circuit diagram of an address change detecting circuit used in the FIG. 13 circuit; 
     FIG. 18 is a circuit diagram of a delay circuit used in the FIG. 13 circuit; 
     FIG. 19 is a circuit diagram of a precharge signal generating circuit used in the FIG. 13 circuit; 
     FIG. 20 shows timing chart useful in explaining the operation of the semiconductor device of FIG. 13 when a chip enable signal is &#34;1&#34;; 
     FIG. 21 is a circuit diagram of a dummy address buffer circuit used in the FIG. 13 circuit; 
     FIG. 22 is a circuit diagram of a circuit for obtaining a delay chip operation signal used in the FIG. 13 circuit; 
     FIG. 23. is a circuit diagram of a row decoder in the FIG. 13 circuit; 
     FIG. 24 is a circuit diagram of a dummy row decoder used in the FIG. 13 circuit; 
     FIG. 25 is a circuit diagram of a dummy row line used in the FIG. 13 circuit; 
     FIG. 26 shows a timing chart for explaining the operation of the FIG. 13 circuit when the chip enable signal shifts to an operation mode; 
     FIG. 27 is a block diagram of a sixth embodiment of a semiconductor device according to the present invention; and 
     FIG. 28 is a circuit diagram including a sense amplifier and a sense amplifier drive circuit used in the FIG. 27 circuit. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     An embodiment of a semiconductor device according to the present invention will be described referring to FIG. 6. A semiconductor memory device comprises a row decoder 10, a plurality of memory cell arrays 14 1  to 14 n  connected to a row decoder through row lines, a plurality of column select circuits 18 1  to 18 n  connected to the memory cell arrays through column lines, a column decoder 20 connected to column select circuits 18 1  to 18 n , sense amplifiers 22 1  to 22 n  correspondingly connected to the column select circuits 18 1  to 18 n , output buffer circuits 24 1  to 24 n  correspondingly connected to sense amplifiers 22 1  to 22 n , and depletion type MOS transistors 36 connected to the output lines of the column decoder 20 between the adjacent column select circuits 18 1  to 18 n . A power source voltage Vc is supplied to the gate of the MOS transistors 36. 
     With such an arrangement, upon operation of the column decoder 20, voltages appearing on the output lines of the column decoder 20 are sequentially delayed by the depletion type MOS transistors 36 and the delayed ones are transferred along the output lines. Accordingly, the column select circuits 18 1  to 18 n  are driven with given time lags, so that column lines of the memory cell arrays 14 1  to 14 n , one for each array, are never selected simultaneously. The times that the bit data from the memory cell arrays are led to the corresponding external output terminals, are made to differ. For this reason, the memory output signals are not changed concurrently. As a result, the large current never flows. 
     The difference of the drive times of the column select circuits, when compared with the operating time of the memory system, is small and negligible. The output lines of the column decoder have a load capacitance smaller than that of the row lines. Since the column lines are normally made of aluminum, the time from an instant that the address input signal changes till the potential on the output lines of the column decoder changes is shorter than the time from an instant that the address input signal changes till the potential on the row lines changes. There is no problem of the speed down of the memory data reading. 
     A second embodiment of a semiconductor device according to the present invention will be described referring to FIG. 7. The semiconductor device is comprised of two memory cell arrays, two column select circuits, and two sense amplifiers for one output buffer. Further, it has a first column decoder 20 1  and a second column decoder 20 2 . The first column decoder 20 1  drives column select circuit 18 11  and 18 12  to 18 n1  and 18 n2 . The second column decoder 20 2  drives sense amplifiers 22 11  and 22 12  to 22 n1  and 22 n2 . Depletion type MOS transistors 36 1  are connected to the column decoder output lines between a pair of column select circuits 18 11  and 18 12  and a pair of the column select circuits 18 21  and 18 22 . In this way, the depletion MOS transistors 36 1  are coupled with the column decoder output lines every two column select circuits. Similarly, depletion type MOS transistors 36 2  are connected to the column decoder output lines between a pair of the sense amplifiers 22 11  and 22 12  and a pair of the sense amplifiers 22 21  and 22 22 . In this way, the depletion MOS transistors 36 2  are coupled with the column decoder output lines every two sense amplifiers. 
     With such connection, the drive start times of the column select circuits by the first column decoder 20 1  are made to differ. The drive start times of the column select circuits by the second column decoders 20 2  are similarly made to differ. Accordingly, the output buffers 24 1  to 24 n  are not changed concurrently when the column address changes. 
     When two sense amplifiers are switched, the second column decoder 20 2  may be arranged so as to provide address data A and the inverted data A. In other words, the second column decoder 20 2  may be an address buffer circuit. 
     In FIG. 7, the MOS transistors 36 1 , which are used for making the drive start times differ, may be omitted, if the circuit is arranged such that pulses are generated in synchronism with changes of the column addresses, the second column decoder 20 2  and the paired sense amplifiers 22 11  and 22 21  to 22 n1  and 22 n2  are dynamically driven and the output signal is produced from the second column decoder 20 2  following the output signal from the first column decoder 20 1 . 
     FIGS. 8A to 8E show some examples used for the depletion type MOS transistors 36, 36 1  and 36 2  in the above-mentioned embodiment. The depletion type MOS transistors shown in FIGS. 8A and 8B are arranged such that the gate of the transistor is connected to the column decoder side or the opposite side in the circuit, respectively. The transistors of FIGS. 8C and 8D are the combinations of the MOS transistors of FIGS. 8A and 8B. FIG. 8E shows a circuit in which two inverters are series-connected. 
     It is possible to make the drive start times of the column select circuits or the sense amplifiers different by the column decoders. Accordingly, the instantaneous current caused when the capacitance of the output terminals are driven is reduced. 
     A third embodiment of a semiconductor device will be described referring to FIG. 9. FIG. 9 shows an output buffer circuit of a central processing unit. The output buffers 28 1  to 28 n  provided between the external bus and the internal bus are controlled by the control signal S. When the control signal S is logic &#34;0&#34;, the output buffer produces data. In this case, delay means are provided for preventing the output buffers 28 1  to 28 n  from being simultaneously turned on. The delay means are the depletion type MOS transistors 36 the gate of which are connected to the input side of the control line 38 to which the control signal S is applied. The MOS transistor 36 functions in order that a transfer delay time of the control signal S when the control signal S changes its logical level from &#34;1&#34; (high) to &#34;0&#34; (low) is longer than that when the control signal S changes from &#34;0&#34; to &#34;1&#34;. Since the gate of the transistor 36 is connected to the control signal input side of the control line, there is a time difference between the cases that the gate of the transistor 36 is set at high level and that it is set at low level. Accordingly, the output buffers 28 1  to 28 n  do not produce data concurrently. Therefore, the peak current is not increased. The reason why the transfer times are made to differ in these level change situations is that when the output buffers produce output signals to the external bus, the signal producing times must be made to differ. All the output buffers must be set in a high impedance state as soon as possible, when the control signal S becomes high in level, that is, when no signal is produced, since the signals from the other devices are also outputted to the external bus. 
     A fourth embodiment of a semiconductor device according to the present invention will be described referring to FIGS. 10 to 12. In the present embodiment, the output buffers 28 1  to 28 n  are controlled by paired control signals A and B. In order to prevent the output buffers 28 1  to 28 n  from turning on simultaneously, delay means 36 similar to those in the third embodiment are provided on the control line 38 1  for the control signal A. A signal a 1  not delayed is applied to the output buffer 28 1  and a delayed signal a 2  is applied to the output buffer 28 2 . Similarly, the most delayed signal a n  is applied to the output buffer 28 n . 
     FIG. 11 shows a practical arrangement of each of the output buffers 28 1  to 28 n  shown in FIG. 10. The output buffer is comprised of transistors Q 1  to Q 18 . The enhancement type MOS transistors Q 1  connected at the gate to the internal bus and the depletion type MOS transistor Q 2  form an inverter I 11 . The output signal from the inverter I 11  is supplied to an inverter I 22  made up of the enhancement type MOS transistor Q 3  and the depletion type MOS transistor Q 4 . The output signal from the inverter I 11  is supplied to the gates of the depletion type MOS transistor Q 6  and the enhancement type MOS transistor Q 7 . The output signal from the inverter I 22  is supplied to the gates of the enhancement type MOS transistor Q 5  and the depletion type MOS transistor Q 8 . A node between the transistors Q 5  and Q 6  is connected to the gate of the enhancement type MOS transistor Q 9 . The node between the transistor Q 7  and Q 8  is connected to the gate of the enhancement type MOS transistor Q 10 . The node between the transistors Q 9  and Q 10  is connected to the external bus. 
     The output line of the inverter I 11 , i.e. the node between the transistors Q 1  and Q 2 , is grounded through the enhancement type MOS transistor Q 11  of which the gate receives the control signal A and the enhancement type MOS transistor Q 12  of which the gate receives the control signal B. The output line of the inverter I 22 , i.e. the node between the transistors Q 3  and Q 4 , is grounded through the enhancement type MOS transistor Q 13  receiving at the gate the control signal A and the enhancement type MOS transistor Q 14  receiving at the gate the control signal B. The node N1 between the transistors Q 5  and Q 6  is grounded through the enhancement type MOS transistor Q 15  receiving at the gate the control signal A and the enhancement type MOS transistor Q 16  receiving at the gate the control signal B. The node N2 between the transistors Q 7  and Q 8  is grounded through the enhancement type MOS transistor Q 17  receiving at the gate the control signal A and the enhancement type MOS transistor Q 18  receiving at the gate the control signal B. 
     The operation of the output buffers 28 1  to 28 n  thus arranged will be described referring to FIG. 12. When the control signals A and B are high in level, the potential at the nodes N1 and N2 are low in level. In this situation, all the buffer circuits do not operate. When the control signal A changes from high to low in level at time T1, the not delayed signal a 1  is applied to the output buffer 28 1 . The control signal B changes in synchronism with the control signal A. Accordingly, the transistors Q 11  to Q 18  are in an OFF state, so that data on the internal bus is outputted to the external bus. 
     The delayed control signals a 2  to a n  are supplied to the output buffers 28 2  to 28 n  in succession. When the control signal a n  changes from high to low in level at time T2, the output buffer 28 n  produces data. 
     When the control signals A and B change from low to high at time T3, and the control signal a 1  and the control signal B are applied to the output buffer 28 1  concurrently. Output buffer 28 1  has a high impedance. In this case, the control signal B is supplied to the output buffers 28 2  to 28 n . Accordingly, the nodes N1 and N2 of the output buffers 28 2  to 28 n  are grounded. As a result, the output buffers 28 2  to 28 n  are also in a high impedance state. Then, all the output buffers 28 1  to 28 n  are in a high impedance state at time T3. 
     The semiconductor device as mentioned above can operate a plurality of output buffers with different time lags in a data outputting mode. In a nonoperating mode, the plurality of output buffers can be stopped concurrently. Consequently, the instantaneous peak current can be reduced. 
     A fifth embodiment of the semiconductor device will be described referring to FIG. 13. The semiconductor device comprises a row decoder 10, a plurality of memory cell arrays 14 1  to 14 n  connected to the row decoder 10 through the row line 12, a plurality of column select circuits 18 1  to 18 n  connected to the memory cell arrays 14 1  to 14 n  through the column lines 16, a column decoder 20 connected to the column select circuits 18 1  to 18 n , sense amplifiers 22 1  to 22 n  connected to the corresponding column select circuits 18 1  to 18 n , output buffer circuits 24 1  to 24 n  connected to the corresponding sense amplifiers 22 1  to 22 n , precharge circuits 33 1  to 32 n  connected to the column lines of the memory cell arrays 14 1  to 14 n , and a precharge time setting circuit 40 for setting precharge times of the precharge circuits 32 1  to 32 n . The precharge time setting circuit 40 determines the precharge start times and the precharge stop times based on a distance from the row decoder 10 to the memory cell arrays 14 1  to 14 n . 
     The precharge time setting circuit 40 is comprised of dummy row line 42, a delay circuit 44, an address buffer circuit 46, an address data detecting circuit 48, a circuit 50 for obtaining a delayed chip enable signal, a dummy address buffer circuit 52, a dummy row decoder 54 and precharge signal generating circuits 56 1  to 56 n . 
     The column line precharge circuits 32 1  to 32 n  for precharging the column lines 16 of the memory cell arrays 14 1  to 14 n  are under control of the precharge signals PC 1  to PC n , respectively. 
     The precharge start is determined by the address buffer circuit 46, the address data detecting circuit 48, the delay circuit 44 and precharge signal generating circuits 56 1  to 56 n . The precharge stop time is determined by the address buffer circuit 46, the dummy address buffer circuit 52, the dummy row decoder 54, the dummy row line 42 and precharge generating circuits 56 1  to 56 n . 
     The dummy row line 42 has the same resistance and capacitance as that of the row line 12 and is provided for all the memory cell arrays 14 1  to 14 n . 
     Each of the precharge signals PC 1  to PC n  is correspondingly produced every time each of the address signals Ao to Am in the address buffer circuit 46 is produced. Changes of the address signals Ao to Am are detected by the address data detecting circuit 48. A signal PCS from the address data detecting circuit 48 is inputted to the delay circuit 44. The output signals PCS 1  to PCS n  from the delay circuit 44 are inputted to the precharge signal generating circuits 56 1  to 56 n , respectively. Then, the precharge signal PC 1  to PC n  delayed corresponding to the memory cell arrays 14 1  to 14 n  rise, respectively. The precharge signals PC 1  to PC n , respectively, fall in accordance with changes of potentials at the nodes F 1  to F n  on the dummy row line 42 corresponding to the memory cell arrays 14 1  to 14 n . 
     The dummy row decoder 54 and the dummy address buffer circuit 52 are provided so that the dummy row line 42 may be selected at the same time when the row line 12 is selected in accordance with the address signals Ao to Am. 
     The precharge signal generating circuits 56 1  to 56 n  detect potential changes DS 1  to DS n  at the nodes F 1  to F n  on the dummy row line 42 and the output signals PCS 1  to PCS n  from the delay circuit 44, and produce precharge signals PC 1  to PC n , respectively. 
     The prior semiconductor device determines the precharge time depending on a potential at the node E n  on the row line of FIG. 3. The semiconductor device according to the present invention checks rises of the potentials at the nodes F 1  to F n  on the dummy row line, and forms a precharge signal PC 1  at the node F 1 , the precharge signal PC 2  at the node F 2 , . . . , the precharge signal PC n  at the node F n . The precharge times of the memory cell arrays 14 1  to 14 n  are determined by the signals PC 1  to PC n , respectively. 
     The transfer times of data from the memory cells to the output buffers 24 1  to 24 n  are shorter as the memory cells are located closer to the row decoder 10. Accordingly, the sense amplifiers 22 1  to 22 n  and the output buffers 24 1  to 24 n  are not operated concurrently, resulting in great decrease of the instantaneous peak current. In the prior semiconductor device, data is outputted at a time point that the node E n  (see FIG. 3) becomes &#34;1&#34; in level. In this respect, the entire time till the data is outputted is never longer than that of the prior one. 
     The dummy row line 42 changes its potential from &#34;0&#34; to &#34;1&#34;, like the selected row line 12, when the address input signal changes, as shown in FIG. 14. The node F 1  nearest the row decoder 10 first rises in level and the node F n  farthest from the row decoder 10 last rises. By detecting a potential change on the dummy row line 42, a pulse width of each of the precharge signals PC 1  to PC n  is determined, as shown in FIG. 15, depending on the potential rises at the nodes F 1  to F n . Precisely, when the potential at the node F 1  on the dummy line 12 rises, the signal PC 1  falls to stop the precharge. When the potential at the node F 2  rises, the signal PC 2  falls to stop the precharge. Similarly, when the potential at the node F n  rises, the signal PC n  falls to stop the precharge. As shown in FIG. 15, the precharge signal PC n  corresponds to the precharge signal PC of the prior semiconductor device (see FIGS. 3 and 4). These signals PC 1  to PC n  become &#34;1&#34; in level in synchronism with a change of the address signal. In design, the precharge start times of the signals PC 1  to PC n  are made different each other, allowing for the decrease of the instantaneous peak current. 
     An arrangement of the precharge time setting circuit 40 will be described. FIG. 16 shows the address buffer circuit 46 for transferring address input data Ai (i=0, . . . , m) to the row decoder 10 and the column decoder 20. In the circuit, an enhancement type MOS transistor T1 receiving at the gate a chip enable signal CE, a depletion type MOS transistor T2 of which the gate and source are interconnected each other, and an enhancement type MOS transistor T3 receiving at the gate address data Ai are connected between the power sources Vc and Vs. The transistors T2 and T3 make up a first inverter I 1 . A transistor T4 receiving at the gate the inverted signal CE of the signal CE is connected between the output terminal of the inverter I 1  and the power source Vs. Similarly, the transistors T5 to T7 are connected between the power source Vc and Vs. The output signal from the first inverter I 1  is inputted to the gate of the transistor T7. The transistors T6 and T7 make up a second inverter I 2 . A transistor T8 receiving at the gate the inverted signal CE of the signal CE is inserted between the output terminal of the second inverter I 2  and the power sourve Vs. Transistors T9 and T12 are arranged similarly. The first buffer B1 is made up of transistors T13 and T14 and a second buffer B2 is made up of transistors T15 and T16. Transistors T17 and T18 having at the gate the inverted signal CE are connected to the output terminals of the first and second buffer circuits B1 and B2. The output signal of the second inverter I 2  is applied to the gates of the transistors T13 and T16. The output of a third inverter I 3  is applied to the gates of the transistors T14 and T15. 
     In the specification, the output signal from the first inverter I 1  is designated by Ci; the output signal from the second inverter I 2  by Di; the output signal from the first buffer B1 by Ai&#39;; the output of the second buffer B2 by Ai&#39;. 
     The address buffer circuit operates when the chip enable signal CE is &#34;1&#34; and the inverted signal CE is &#34;0&#34;. The circuit does not operate when CE=&#34;0&#34; and CE=&#34;1&#34;. The current flowing into the circuit at this time is substantially zero. When CE=&#34;0&#34;, the address buffer output signals Ai&#39; and Ai&#39; are both &#34;1&#34; irrespective of the address data Ai. 
     Explanation will be given when the address Ai changes under a condition that the chip is selected, that is, CE=&#34;1&#34; and CE=&#34;0&#34;, how the precharge signals PC 1  to PC n  are produced. 
     In FIG. 16, the signal Ci is the inverted signal of the address data Ai and is delayed behind the address data Ai by the time taken for the signal to pass through the inverter I 1 . The signal Di is the inverted signal of the signal Ci and delayed behind the signal Ci by the time taken for it to pass through the inverter I 2 . The output signal Ai&#39; delays behind the signal Di by the time taken for it to pass through the inverter I 3  and the first buffer circuit B1. The output signal Ai&#39; delays behind the signal Di by the time taken for it pass through the inverter I 3  and the second buffer circuit B2. 
     FIG. 17 shows a practical arrangement of the address change detecting circuit 48. The address change detecting circuit 48 is comprised of enhancement type transistors T19 and T20, depletion type transistors T21 and T22, NOR gates 60 and 62, and enhancement type transistors T23 and T24. The enhancement type transistor T19 receives at the drain the signal Ci from the inverter I 1  and at the gate the signal Ai&#39; from the buffer B1 of FIG. 16. The transistor T20 receives the signal Di from the inverter I 2  of FIG. 16 and at the gate the signal Ai&#39; from the buffer B2 of FIG. 16. The transistor T21 is connected at the drain to the source of the transistor T19 and at the gate and source to the power source Vs. The transistor T22 is connected at the drain to the source of the transistor T20 and at the gate and source to the power source Vs. The output signal from the transistor T19, and the signals Ci&#39; from the transistor T19, the output signal from the NOR gate 62 and the signal Di&#39; from the transistor T20 are inputted to the NOR gate 60. The output signal from the NOR gate 60 and the potential DS n  at the node F n  of the row line 12 are inputted to the NOR gate 62. The output signal from the NOR gate 62 is inputted to the gate of the transistor T23. The output signal from the NOR gate 60 is applied to the gate of the transistor T24. The NOR gates 60 and 62 make up a flip-flop. The transistors T23 and T24 are arranged between the power sources Vs and Vc in series. The output signal from the buffer circuit B3 serves as a precharge set signal PCS. 
     The signal PCS is led to a delay circuit containing a resistor R and a capacitor C shown in FIG. 18. The delay circuit 44 produces signals PCS 1  to PCS n  delayed properly. The delay circuit arrangement is illustrated only by way of example and may be constructed by proper component if its function is secured. 
     The signals PCS 1  to PCS n  are respectively inputted to corresponding precharge signal generating circuits 56 1  to 56 n  shown in FIG. 19. The precharge signal generating circuits 56 1  to 56 n  are each a flip-flop made up of the NOR gates 64 and 66. Potentials DS 1  to DS n  at the nodes F 1  to F n  of the dummy row line are applied to the NOR gate 66. The flip-flop produces precharge signals PC 1  to PC n  corresponding to the precharge circuits 32 1  to 32 n . 
     The operations of the address buffer circuit 46, the address detecting circuit 48, the delay circuit 44, and the precharge signal generating circuits 56 1  to 56 n  will be described referring to signal waveforms of FIG. 20. In the circuit shown in FIG. 16, the signal Ci is delayed by the switching time of the inverter I 1  behind the address input signal Ai and the signal Di is delayed by the time of the inverters I 1  and I 2  behind the signal Ai. The address buffer output signal Ai&#39; is delayed by the time of the inverter I 3  and the buffer B1 behind the signal Di. The address buffer output signal Ai&#39; is delayed by the time of the inverter I 3  and the buffer B2 behind the signal Di. When the signal Ci changes from &#34;0&#34; to &#34;1&#34;, the signal Ci&#39; also changes from &#34;0&#34; to &#34;1&#34; through the transistor T19. Immediately after the change, in the circuit of FIG. 17, the delay of the address buffer output signal Ai&#39; causes the signal Ci&#39; to discharge through the transistor T21 (become &#34;0&#34;) and changes the signal Ai&#39; to &#34;0&#34;. Accordingly, when the signal Ai changes from &#34;1&#34; to &#34;0&#34;, the signal Ci&#39; becomes &#34;1&#34; instantly. 
     Similarly, the signal Di&#39; becomes &#34;1&#34; instantly when the signal Ai changes from &#34;0&#34; to &#34;1&#34;. 
     Accordingly, the output signal from the NOR gate 60 becomes &#34;0&#34; in level. The potential on the dummy row line F n  is &#34;0&#34; at this time, and therefore the output signal of the NOR gate 62 becomes &#34;1&#34;. The result is that the transistor T23 becomes ON while the transistor T24 becomes OFF, and the precharge set signal PCS becomes &#34;1&#34;. Since the signals Co&#39; to Cm&#39; and Do&#39; to Dm&#39; corresponding to the respective addresses Ao to Am are inputted to the NOR gate 60, the precharge set signal PCS changes to &#34;1&#34; when either of the addresses changes. The signals PCS becomes signals PCS 1  to PCS n  which are successively delayed by the circuit of FIG. 18. 
     If the signal PCS 1  is inputted to the NOR gate 64 in the flip-flop of the precharge signal generating circuit 56, the node F 1  potential is applied to the NOR gate 66. At this time, the node F 1  potential is &#34;0&#34;, so that the output signal of the NOR gate 66 is &#34;1&#34; if the signal PCS 1  is &#34;1&#34;. Thus, the precharge signal PC 1  corresponding to the precharge circuit 32 1  is obtained. Similarly, the signals PC 2  to PC n  corresponding to the respective precharge circuits 32 2  to 32 n  are formed. In this way, the column line 16 is precharged. 
     A following circuit is a circuit for stopping the precharge. FIG. 21 is a circuit 52 for producing dummy address buffer output signals Bi&#39; and Bi&#39; to be applied to the decoder for the dummy row line 42. As in the circuit shown in FIG. 16, the transistors T25 to T27 are connected between the power sources Vc and Vs. The chip enable signal CE is applied to the gate of the transistor T25. An address buffer output signal Ai&#39; is inputted to the gate of the transistor T27. The transistors T26 and T27 form an inverter I 4 . The transistors T28 and T29 form an inverter I 5 . A delay circuit 70 including a transistor T30 connected at the gate to the power source Vc and a capacitor C1 at one end to the power source Vs is provided between the inverters I 4  and I 5 . 
     The transistors T31 to T33 are connected between the power sources Vc and Vs. The chip enable signal CE is applied to the gate of the transistor T31. An address buffer output signal Ai&#39; is inputted to the gate of the transistor T33. Transistors T32 and T33 form an inverter I 6  and the transistors T34 and T35 form an inverter I 7 . A delay circuit 72 including a transistor T36 and a capacitor C2 is connected between the inverters I 6  and I 7 . The gate of a transistor T37 is coupled to the output terminal of the inverter I 5 , the drain is supplied with the buffer output Ai&#39; and the dummy address output Bi&#39; is outputted from the source. The gate of a transistor T38 is coupled to the output terminal of the inverter I 7 , at the drain to the buffer output Ai&#39;, and at the source to the inverted dummy address output Bi&#39;. A transistor T39 receiving at the gate a delayed chip enable signal CED is provided between the address output Bi and Bi&#39;. 
     FIG. 22 shows a circuit 50 for forming the delayed chip enable signal CED. Transistors T40 and T41 form an inverter I 8 . Transistors T42 and T41 form an inverter I 9 . A delay circuit 74 including a transistor T44 and a capacitor C3 is provided between the output terminal of the inverter I 8  and the input terminal of the inverter I 9 . A chip enable signal CE is inputted to the inverter I 8  and the inverter I 9  produces a delayed chip enable signal CED delayed a given time. 
     In the circuit 52 in FIG. 21, when the signal CE is &#34;1&#34;, the delayed enable signal CED is also &#34;1&#34;. Delayed address buffer signals AiD&#39; and Ai&#39;D are produced by delaying the signals Ai&#39; and Ai&#39; a given time by the delay circuits 70 and 72, respectively. When the signal CED is &#34;1&#34;, the signal Bi&#39; and Bi&#39; become in-phase signals as the result of the short circuiting by the transistor T39. When the buffer output Ai&#39; changes from &#34;1&#34; to &#34;0&#34;, the signal Bi&#39; changes from &#34;1&#34; to &#34;0&#34;. At this time, the signal Ai&#39;D is &#34;1&#34; and Ai&#39;D is &#34;0&#34;. These signals Ai&#39;D and Ai&#39;D become &#34;0&#34; and &#34;1&#34; with a given time delay with respect to the signals Ai&#39; and Ai&#39;, respectively. At this time, the signal Ai&#39; is &#34;1&#34;. Accordingly, the signals Bi&#39; and Bi&#39; return to &#34;1&#34; in level. 
     FIG. 23 shows an ordinary row decoder 10 for selecting a given row line 12 in response to address data Ao&#39; to Am&#39;. FIG. 24 shows a dummy row decoder 54 for selecting a desired row line 42. The address buffer output signals Ai&#39; and Ai&#39; are applied to the circuit of FIG. 23 to select the row line 12. The dummy buffer output signals Bi&#39; and Bi&#39; are applied to the FIG. 24 circuit to select a desired dummy row line 42. The dummy address output signals Bo&#39; and Bo&#39;, . . . , Bi&#39; and Bi&#39;, . . . , Bn&#39; and Bn&#39; are applied to the dummy row decoder of FIG. 24 substantially at the same time as the address buffer outputs Ai&#39; and Ai&#39; are inputted to the row decoder 10 of FIG. 23. 
     In FIG. 24, there is shown a decoder for selecting one dummy row line in response to any one of the dummy address outputs by using a NOR gate 76. Alternatively, by using (n+1) dummy row lines, single dummy row lines are respectively selected, one for one, by dummy address output signals Bo&#39; and Bo&#39;, . . . , Bi&#39; and Bi&#39;, . . . , Bn&#39; and Bi&#39;. Substantially at the same time as the row line 12 selected by the row decoder 10 changes from &#34;0&#34; to &#34;1&#34; in level, the dummy row line 42 changes from &#34;0&#34; to &#34;1&#34;. The signal DRL is inputted to the dummy row line 42 of FIG. 25 to drive the nodes F 1  to F n  to produce signals DS 1  to DS n . The signals DS 1  to DS n  are inputted to the flip-flop of FIG. 19 to render the precharge signals PC 1  to PC n  &#34;0&#34; sequentially. Similarly, the signal DS n  is applied to NOR gate 62 of FIG. 17 to render the signal PCS &#34;0&#34;. In this way, the precharge cycles of the precharge circuits 32 1  to 32 n  are finished in succession. 
     An operation in which the chip enable signal CE changes from &#34;0&#34; to &#34;1&#34; and the signal CE changes from &#34;1&#34; to &#34;0&#34;, will be described referring to FIG. 26 illustrating voltage waveforms. Also when the chip shifts from a non-operation mode to an operation mode, the signals Ci&#39; and Di&#39; are produced. The operating process until the precharge set signals PCS 1  to PCS n  and the precharge signals PC 1  to PC n  become &#34;1&#34; is exactly the same as that as mentioned above. When the chip operation signal CE changes from &#34;0&#34; to &#34;1&#34;, the delay chip operation signal CED shown in FIG. 22 changes from &#34;0&#34; to &#34;1&#34; after a given time. Accordingly, when the address buffer output signal Ai&#39; changes from &#34;1&#34; to &#34;0&#34;, the signal CED is left &#34;0&#34;. Therefore, the signal Bi&#39; changes from &#34;1&#34; to &#34;0&#34;, and the signal Bi&#39; remains &#34;1&#34;. 
     When the delayed chip operating signal CED becomes &#34;1&#34; in level after a fixed time, the signal Ai&#39;D is also &#34;0&#34; and thus the signal Bi&#39; changes to &#34;1&#34;. When the signal Bi changes its level from &#34;1&#34; to &#34;0&#34;, the row line is selected by the address buffer outputs Ai&#39; and Ai&#39; in the row decoder 10. At this time, the signal Bi, changes its logical level from &#34;1&#34; to &#34;0&#34;, so that the selected dummy row line 16 changes its logical level from &#34;0&#34; to &#34;1&#34;. Then, the potential signals DS 1  to DS n  at the nodes F 1  to F n  on the dummy row line 42 are applied to the flip-flop in FIG. 19. The precharge signals PC 1  to PC n  change their logical state from &#34;1&#34;  to &#34;0&#34;. Accordingly, the operation of the precharge circuit 32 1  to 32 n  completes. Also when the chip enable signal CE changes its logical state from &#34;0&#34; to &#34;1&#34;, the circuit operates well. 
     A sixth embodiment of the present invention will be described referring to FIG. 27. 
     FIG. 27 shows a semiconductor device having circuits 80 1  to 80 n  for operating sense amplifiers 22 1  to 22 n  in synchronism with precharge signals PC 1  to PC n . The circuit arrangement of FIG. 27 is the same as that of FIG. 13 except for the circuits 80 1  to 80 n . FIG. 28 is a practical arrangement of the sense amplifier 22 1  and the circuit 80 1  for operating it. The circuit 80 1  is an inverter I 10  made up of transistors T50 and T51. The precharge signal PC 1  is applied to the gate of the transistor T50. The sense amplifier 22 1  is made up of transistors T52 to T57. The output signal from the inverter I 10  is applied to the gates of the transistors T52 and T53. A pair of column lines Q n  and Q n  are connected to the gates of depletion type transistors T56 and T57. 
     With such an arrangement, when the precharge operation to the column lines Q n  and Q n  terminates and the data in the memory cell selected appear on the column lines Q n  and Q n , the precharge signals PC 1  to PC n  become &#34;0&#34; in level. As a result, the transistors T52 and T53 turn on and the sense amplifier 22 1  starts its operation. 
     Subsequently, the sense amplifier 22 2  starts its operation in response to the precharge signal PC 2  and the sense amplifier 22 n  responds to the precharge signal PC n  to start its operation. Since the operating times of the sense amplifiers 22 1  to 22 n  are shifted from one another, the instantaneous peak current may further be reduced. When the information of the memory cell selected appears on the column lines Q n  and Q n , the precharge signals PC 1  to PC n  for operating the sense amplifiers 22 1  to 22 n  are produced. Therefore, the operation of the sense amplifiers 22 1  to 22 n  is speeded up. 
     In the above-mentioned embodiments, the precharge period is set by detecting a logical level change from &#34;0&#34; to &#34;1&#34; on the dummy row line 42. Alternatively, the precharge period may be set by detecting a logical level change from &#34;1&#34; to &#34;0&#34; on the same line. 
     The above-mentioned embodiment employs the same number of the output buffer circuits as that of the precharge signals PC 1  to PC n . If the number of the latter is larger than that of the former, however, the peak current can be further reduced. In a situation where the requirement for the value of the peak current is not strict, the number of the precharge signal may be smaller than that of the buffer circuits.