Write Control Circuit for a High-Speed Memory Device

This invention relates to a write control circuit for a memory device, and more specifically to a write control circuit adapted for use in a very high-speed semiconductor memory device.

The write operation of a semiconductor memory device is controlled according to a write enable (WE) signal supplied externally. In a conventional high-speed semiconductor memory device, as shown in FIG. 3, the WE signal itself, after amplification by an amplifier-gate 6, is directly applied to sense amplifiers 14.

An improved write control circuit adapted for use in a high-speed semiconductor memory device is disclosed in Electronic Design, Dec. 27, 1984, pp. 157-170. In this circuit, as shown in FIG. 4, the WE signal is latched in a latch 15 by an externally supplied clock signal (CLK). The output of this latch activates a write timing generator 16 whose output signal is applied to the sense amplifiers 14. This timing mechanism not only eliminates many difficulties in the timing of various signals within a high-speed semiconductor memory device but also permits overlapping of input operations and output operations, taking advantages of the capability of forming a read cycle and a write cycle equal in length and timing.

For the conventional circuit shown in FIG. 3, the duration of the WE signal must be shorter than a write cycle. Even for the improved circuit shown in FIG. 4, the duration of the WE signal can not exceed the write cycle. On the other hand, for a very high-speed bipolar or GaAs memory device like those used as a cache memory or a register group in a supercomputer, a very short cycle time, for example a few nanoseconds or so, is required. In a semiconductor memory device which is required to operate at such a very high speed, when mounting conditions are taken into account, it is not easy to control the write operation correctly by means of the WE signal with a duration equal to or shorter than the write cycle, owing to an substantial decrease in pulse duration resulting from waveform deterioration, noises, skews, and the like. Where the pulse duration is exceedingly short, it becomes very difficult to precisely control the timing of the rising or falling edge or the pulse duration.

An object of the present invention is to permit the utilization of WE signals wide enough to obviate the above-mentioned problem of timing for the reliable write operation of a very high-speed memory device.

The write control circuit of this invention receives first and second write enable signals each having a duration equal to two write cycles, with the phase difference between these signals being equal to at least one write cycle. The first and second write enable signals are converted into first and second write mode signals, respectively, each having a duration equal to one write cycle, with the second write mode signal having a phase difference relative to the first write mode signal equal to the phase difference between the first and second write enable signals. A circuit is included which generates a write execute signal in each signal period of the first and second write mode signals.

Thus, the present invention uses write enable signals twice or more as wide as those used in prior art memory devices, and yet two or more successive write cycles can take place without error. Consequently, the controlling of timing and duration of the write enable signal becomes easy, and the influences of attenuation, noises, skews, and the like diminish, resulting in a remarkable decrease in write errors for high-speed memory devices.

FIG. 1 shows a write control circuit as an embodiment of the present invention;

FIG. 2 shows the waveforms of signals appearing at various points of the circuit of FIG. 1; and

FIG. 3 and FIG. 4 show, by way of comparison, prior art write control circuits.

FIG. 1 shows the logic structure of an example of the write control circuit according to the present invention, and FIG. 2 shows the waveforms of signals appearing at various points of the circuit shown in FIG. 1. The circuit shown in FIG. 1 is arranged within an integrated circuit memory device. CLKP, CLK0, CLK1 and CLK2 are externally supplied clock signals. As is shown in FIG. 2, the clock pulses of CLK0 and CLK1 each have an interval of two operation cycles, and there is a phase difference of one operation cycle between these two clock signals. The clock pulses of CLK2 have an interval of one operation cycle. CLKP has a duration and an interval both equal to two operation cycles, and is synchronized with CLK0. A write cycle and a read cycle for this embodiment have the same length. Two series of write enable signals, WEF and WES, are externally supplied. Each of WEF and WES has a duration equal to two operation cycles, and there is a phase difference of at least one operation cycle between them. WEF is supplied in synchronism with CLK0, and WES is supplied in synchornism with CLK1. It is obvious that the phase difference between supplied WEF and WES signals corresponds to the interval between the write requests that call the supplied WEF and WES signals, respectively, for the execution thereof. When two consecutive write operations are requested, the phase difference is equal to one operation cycle, as shown in FIG. 2. In the present embodiment, the phase difference between WEF and WES signals can be any odd number of operation cycles since there is a phase difference of one operation cycle between CLK0 and CLK1, with which the WEF and WES signals are respectively synchronized.

A latch 2 functions as a delay element which generates a signal corresponding to CLKP delayed for a time equal to one operation cycle. An exclusive-OR gate 7, AND gates 8 and 9, a wired-OR 11 and a latch 5 constitute a circuit for converting each of WEF and WES into a write mode signal having an duration equal to one operation cycle.

CLK0, passing through an amplifier gate 6a, sets WEF in a latch 3, while CLK1, passing through an amplifier gate 6b, sets WES in a latch 4. CLK0 also sets CLKP in a latch 1 whose "1" output is set in the latch 2 by CLK1 and at the same time applied to one of the two inputs of the exclusive-OR gate 7. The other input of the exclusive-OR gate 7 receives the output of the latch 2. As a result, the output of the exclusive-OR gate 7 rises to a high level during the first operation cycle in a period during which CLKP is high and also during the first operation cycle in a period during which CLKP is low. The output of the exclusive-OR gate 7 functions as a pitch signal for extracting from each of WEF and WES a write mode signal having a duration equal to one operation cycle. More particularly, the WES output of the latch 4 and the WEF output of the latch 3 are gated at the AND gates 9 and 8 by the output of the exclusive-OR gate 7 and the inverted output thereof, respectively. The outputs of these AND gates are set, through the wired-OR 11, in the latch 5 by CLK2 supplied through an amplifier gate 6c. Accordingly, the write mode signal, that is, the output of the latch 5, is a signal with a duration equal to one operation cycle corresponding to a latter half of either WEF or WES.

CLK2, passing through the amplifier gate 6c, is also supplied to a write pulse generator 12 which generates a train of write pulses in synchronism with CLK2. These write pulses are properly adjusted with respect to set-up time, duration, hold time and the like as required for controlling the write operation of a memory array 13. This train of write pulses is gated at an AND gate 10 by the write mode signal from the latch 5. The gated write pulse, WTPULSE, is sent to sense amplifiers 14. Upon reception of WTPULSE, the sense amplifiers 14 operate as write circuits and execute the writing of data into the memory array 13.