Abstract:
A dynamic random access memory comprises memory cells (MA1-Man) and sense amplifies (SA1-SAn) in a memory array region III and memory cells (MB1-MBn) and sense amplifies (SB1-SBn) in a memory array region IV. In reading operation, first, the sense amplifiers in one region comprising a memory cell designated by an address signal are activated and then sense amplifiers in the other region are activated. As a result, since amplifying operation by the sense amplifiers is performed sequentially, a peak value of a current consumed by the amplification can be reduced.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to a semiconductor memory device and, more particularly, to activation of a sense amplifier thereof. The present invention has particular applicability for a dynamic random access memory device. 
     2. Description of the Background Art 
     FIG. 5 is a block diagram showing one example of a well-known conventional dynamic random access memory (hereinafter referred to as a DRAM). Referring to FIG. 5, the DRAM comprises a memory array 58 comprising memory cells for storing a data signal, an address buffer 54 receiving an address signal to select a memory cell, a row decoder 55 and a column decoder 56 which decode an address signal, and a sense amplifier 63 connected to the memory array 58 and amplifying and reading a signal stored in the memory cell. An input buffer 59 for inputting the data signal and an output buffer for outputting the data signal are connected to the memory array 58 through an I/O gate 57. 
     The address buffer 54 is connected to receive external address signals ext. A0 to A9 or internal address signals Q0 to Q8 generated from a refresh controller 52. The refresh controller 52 drives a refresh counter 53 in response to the timing of RASand CASsignals applied to a clock generator 51. 
     FIG. 6A is a circuit diagram showing a peripheral circuit of the memory array 58 of the DRAM shown in FIG. 5. FIG. 6B is a timing chart for describing its operation thereof. These are seen, for example, on pages 252 to 253 in a Digest of Technical Papers of International Solid State Circuit Conference held on Feb. 15, 1985 (Session XVII). 
     Referring to FIG. 6A, a memory cell M is connected to a bit line BLj and a word line WLi. The memory cell M comprises a capacitor Cs for storing a data signal and an NMOS transistor Qs for switching. A sense amplifier 63 comprises a CMOS flip-flop connected between the bit lines BLj and BLj. This CMOS flip flop comprises a P channel sense amplifier comprising PMOS transistors Q3 and Q4, and an N channel sense amplifier comprising NMOS transistors Q1 and Q2. The CMOS flip-flop is connected to the power supply Vcc and the ground Vss through a PMOS transistor Q11 and an NMOS transistor Q12. The transistors Q11 and Q12 have their gates connected to receive sense trigger signals Soand So, respectively. An equalize circuit 61 comprises an NMOS transistor Q5 connected between the bit lines BLj and BLjand NMO transistors Q6 and Q7 connected in series. The gates of these transistors are connected to receive an equalize signal EQ. 
     A bit line precharge voltage (hereinafter referred to as a V BL ) generation circuit 62 is connected to the junction of the transistors Q6 and Q7 through an NMOS transistor Q10. An I/O gate 57 comprises an NMOS transistor Q8 connected between the bit line BLj and an I/O line and an NMOS transistor Q9 connected between the bit line BLjand an I/ line. The transistors Q8 and Q9 have their gates connected to receive a signal Yj from a column decoder. The signal generation circuit 69 is provided for generating control signals PR, EQ, So and Sofor controlling these circuits. 
     Referring to FIGS. 6A and 6B, a description is made of reading operation and refresh operation of the DRAM. 
     First, the equalize signal EQ and the precharge signal PR are generated from the signal generation circuit 69. The transistors Q10, Q5, Q6 and Q7 turn on in response to these signals and the bit line pair of BLj and BLjare equalized to be brought to VBL (in general a voltage Vcc/2). After a RASsignal falls, the signals EQ and PR change to a low level. Then, a word line signal WLi changes to a high level and the switching transistor Qs of the memory cell M turns on. A voltage of the bit line BLj changes a little when a signal from the memory cell M is applied, whereby a small voltage difference between the bit line BLjand the bit line BLj is generated. 
     On the other hand, at this time, the signals So and Sochange and the sense amplifier is driven. Then, the small voltage difference generated between the bit lines is amplified by the sense amplifier 63. Thereafter, by applying a high level signal Yj, the amplified data signal is applied to the I/O line pair through the transistors Q8 and Q9. 
     In refresh operation, the amplified data signal is not applied to the I/O line pair, but it is only applied to the capacitor Cs of the memory cell again. 
     FIG. 7 is a conceptual diagram showing the corresponding relation between regions of the memory array 58 and the sense amplifier 63 shown in FIG. 5 and the address signal. As shown in FIG. 7, the regions comprising the memory array 58 and the sense amplifier 63 correspond to row address signals RA 8  and column address signals CA 8  and can be divided into four regions I to IV. Therefore, for example, the address signal for designating a certain memory cell in the region IV comprises the row address signal RA 8  of &#34;1&#34; and the column address signal CA 8  of &#34;1&#34;. 
     FIG. 8 is a circuit diagram showing partially the regions III and IV shown in FIG. 7. In the region III, there are provided memory cells MA1 to MAn and sense amplifiers SA1 to SAn which are connected to a bit line pair of BL and BL. Similarly, in the region IV, there are provided memory cells MB1 to MBn and sense amplifiers SB1 to SBn. An activation line SN is connected to the ground Vss through the transistor Q12 and the activation line SP is connected to the power supply Vcc through the transistor Q11. Each of the memory cells and the sense amplifiers has the same circuit structure as that shown in FIG. 6A. 
     An example of prior art of particular interest to the present invention is seen in Japanese Patent Laying-Open Gazette No. 68797/1986. In this prior art, ability to drive sense amplifier is varied in response to a column address signal. 
     Another example of the prior art of particular interest to the present invention is seen in Japanese Patent Laying-Open Gazette No. 20297/1986. This prior art discloses an example of a circuit which drives a plurality of sense amplifiers with signals having different timings. These sense amplifiers are driven without responding to the address signal. 
     A further example of the prior art of particular interest to the present invention is seen in IEEE Journal of Solid State Circuit (VOL. SC-22, No. 5) issued in October 1987 (pages 651-656). In this example, ability to drive a sense amplifier is raised in response to driving signals having different timings. 
     Still another example of the prior art of particular interest to the present invention is seen in Japanese Patent Laying-Open Gazette No. 223994/1984. In this example, there is shown a timing control of the equalization of a bit line pair. 
     FIG. 9 is a timing chart showing changes of each signal when the sense amplifier shown in FIG. 8 is activated. Referring to FIGS. 8 and 9, for example when the data signal of the memory cell MB1 in the region IV is read in reading operation, all sense amplifiers SA1 to SAn and SB1 to SBn in the regions III and IV are activated. More specifically, as described above, the transistors Q12 and Q11 turn on in response to the sense trigger signals So and So. A small voltage generated on the bit line pair of BL and BLin the regions III and IV is amplified by the activation of these sense amplifiers. Since all sense amplifiers in the regions III and IV are activated at the same time, a current Is consumed by the sense amplifiers is increased rapidly and shows a peak value Ia. The rapid increase in this consumption of the current Is causes the supply voltage to drop and this drop of the supply voltage causes the sensitivity of the sense amplifier to deteriorate. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a semiconductor memory device in which a peak value of a current for activating a sense amplifier is reduced. 
     Another object of the present invention is to provide a semiconductor memory device which can prevent a drop in the supply voltage caused by the rapid increase in current consumption. 
     A further object of the present invention is to provide a semiconductor memory device which can prevent deterioration in the sensitivity of a sense amplifier caused by the rapid increase in current consumption. 
     Yet another object of the present invention is to provide a dynamic random access memory in which a peak value of a current for activating a sense amplifier is reduced. 
     Still another object of the present invention is to provide a dynamic random access memory which can prevent a drop in the supply voltage caused by the rapid increase in current consumption. 
     A further object of the present invention is to provide a dynamic random access memory which can prevent deterioration in the sensitivity of a sense amplifier caused by the rapid increase in current consumption. 
     In brief, a semiconductor memory device in accordance with the present invention comprises a memory array comprising a first memory array region including a memory cell designated by an address signal and a second memory array region not including the designated memory cell; a first amplifying circuit amplifying the data signal in the first memory array region; a second amplifying circuit amplifying the data signal in the second memory array region; and a sequentially activating circuit activating the first and second amplifying means in this order in response to an address signal. 
     In operation, first, the data signal in the first array region is amplified in response to the address signal and then the data signal in the second array region is amplified. Since amplifying operation is performed sequentially in this way, a peak value of current consumption for amplification can be reduced. 
     A method for operating a semiconductor memory device in accordance with the present invention comprises the steps of selecting a first memory array region including a memory cell designated by an address signal; selecting a second memory array region not including the designated memory cell; amplifying the data signal stored in the memory cell in the first memory array region; and amplifying the data signal of the second memory array region after the data signal in the fist memory array region is amplified. 
     Since the data signals in the first and second memory array regions are amplified at different timings, the peak value of a current consumed by the amplification can be reduced. 
     The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a block diagram a showing a DRAM in accordance with one embodiment of the present invention; 
     FIG. 2 is a circuit diagram showing an example of an activation signal generating circuit shown in FIG. 1; 
     FIGS. 3A and 3B are circuit diagrams showing separately activated regions of a memory array and sense amplifier shown in FIG. 1; 
     FIG. 4 is a timing chart for describing operation of the DRAM shown in FIG. 1; 
     FIG. 5 is a block diagram showing a conventional DRAM; 
     FIG. 6A is a circuit diagram showing a circuit connected to a conventional bit line pair. 
     FIG. 6B is a timing chart for describing operation of the circuit shown in FIG. 6A; 
     FIG. 7 is a conceptual diagram showing four regions in a memory array and a sense amplifier shown in FIG. 5; 
     FIG. 8 is a circuit diagram showing one portion of regions III and IV shown in FIG. 7; and 
     FIG. 9 is a timing chart for describing operation of the circuit shown in FIG. 8. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 is a block diagram of a DRAM showing one embodiment of the present invention. Referring to FIG. 1, the DRAM is different from a conventional DRAM shown in FIG. 5 in that there is newly provided an activation signal generating circuit 64 which is connected to receive a row address signal RA 8  and a column address signal CA 8  from an address buffer 54. A sense amplifier 63 is connected to receive output signals φa to φd from this activation signal generating circuit 64. 
     FIG. 2 is a circuit diagram showing one example of the activation signal generating circuit 64 shown in FIG. 1. Referring to FIG. 2, the activation signal generating circuit 64 comprises four NOR gates 11 to 14 and inverters 21 to 24 each connected to the output of each of NOR gates 11 to 14. The NOR gate 11 has one input connected to receive a column address signal CA 8  and the other input connected to receive a row address signal RA 8 . Similarly, the NOR gates 12 to 14 are connected to receive signals CA 8  and RA 8 , signals CA 8  and RA 8 , and signals CA 8  and RA 8 , respectively. The output signals φa to φd for activating a sense amplifier are outputted through the inverters 21 to 24, respectively. These output signals φa to φd are applied to the sense amplifier 63 shown in FIG. 1. 
     FIGS. 3A and 3B are circuit diagrams showing regions I to IV of the memory array 58 and the sense amplifier 63 shown in FIG. 1. For example, referring to FIG. 3B, the circuit is different from the conventional circuit shown in FIG. 8 in that sense amplifiers SA1 to SAn in the region III and sense amplifiers SB1 to SBn in the region IV are connected to different activation lines SP1 and SP2, respectively. The activation line SP1 is connected to the power supply through PMOS transistors Q13 and Q14 connected in parallel. The activation line SP2 is connected to the power supply Vcc through PMOS transistors Q15 and Q16 connected in parallel. The gate of the transistor Q13 is connected to receive an output signal φd from the activation signal generating circuit 64 and the gate of the transistor Q15 is connected to receive an output signal φc. The gates of the transistors Q14 and Q16 are connected to receive a sense trigger signal So. 
     The regions I and II have the same circuit structure as that of the regions III and IV as shown in FIG. 3B and are connected to receive output signals φb and φa from the circuit 64. 
     FIG. 4 is a timing chart showing changes of control signals for operating the DRAM shown in FIG. 1. Referring to FIG. 4, as one example, a description is made of a case where the data signal stored in a memory cell MB1 in the region IV shown in FIG. 3B is read. 
     First, a signal RADE for taking in a row address signal RA 8  rises in response to the fall of a RASsignal. The row address signal RA 8  is taken in, in response to the signal RADE. A word line drive signal WD rises in response to the output of the signal RA 8 . Sense trigger signals SO and Sofor activating the sense amplifier are outputted in response to the rise of the signal WD. 
     On the other hand, a signal CADE for taking in a column address signal CA 8  rises in response to the rise of the signal WD. A column address signal CA 8  is taken in, in response to the signal CADE. A signal φc for activating the sense amplifier in the region IV falls in response to the input of the signal CA 8 . The signal CDE for starting operation of a column decoder falls in response to the fall of the RASsignal and the rise of the sense trigger signal So. 
     Looking at the changes of the signals for activating the sense amplifier from a viewpoint of a lapse of time, first the sense trigger signal So rises. Then the signal φc falls and the signal Sofalls. Referring to FIG. 3B, N channel sense amplifiers in the sense amplifiers SA1 to SAn and the SB1 to SBn in the regions III and IV are activated in response to the rise of the signal So. Almost at the same time, P channel sense amplifiers in the sense amplifies SB1 to SBn are activated in response to the fall of the signal φc. Therefore, at this time (time t1), a current Is consumed by the activation of the sense amplifiers shows a peak value Ib as shown in FIG. 4. 
     At a time t2, P channel sense amplifiers in the sense amplifiers SA1 to SAn in the region III are activated in response to the fall of the signal So. Therefore, at this time (time t2), the current Is shows a peak value Ib. The peak value Ib of the current Is is naturally smaller than the peak value Ia of the current Is for activating the conventional sense amplifier shown in FIG. 9 because the sense amplifiers SB1 to SBn and SA1 to SAn in the regions IV and III are sequentially activated at different timings (the time t1 and t2). 
     The supply voltage can be prevented from lowering by reducing the peak value of the current for activating the sense amplifiers. In addition, the sensitivity of the sense amplifier can be prevented from deteriorating. 
     Although a description was made of the example of the DRAM, the present invention is also applicable to another semiconductor memory such as a static random access memory. 
     As described above, since the semiconductor memory device in accordance with the present invention comprises means for sequentially activating amplifying means in the region including a designated memory cell and the region not including the memory cell at different timings in response to the address signal, then it is possible to reduce a peak value of a current consumed by activation. 
     Although the present invention has been described and illustrated in detail, it is clearly understood that the same is by way of illustration and example only and is not to be taken by way of limitation, the spirit and scope of the present invention being limited only by the terms of the appended claims.