Semiconductor integrated circuit

Abstract

A semiconductor integrated circuit according to this invention is characterized by comprising a flip-flop having input terminal means and output terminal means, at least one input gate means having output terminal means connected to the input terminal means, which supplies data to this input terminal means under the control of clock, and at least one output buffer means having input terminal means connected to the output terminal means, to which the output signal of the flip-flop is supplied and which is connected to the output terminal means of the input gate means to receive the data from this input gate means to provide an advance read function.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a semiconductor integrated circuit composed of flip-flops, which receives data with the timing of a clock signal and retains it.

2. Description of the Related Art

Conventional data latch circuits are constructed as shown in FIG. 1A, for example. They are composed primarily of flip-flops using NOR gates. Specifically, the data latch circuit is made up of NOR gates G.sub.101 and G.sub.102 constituting a flip-flop, a NOR gate G.sub.201 serving as an input gate that transfers data D to one input terminal of the flip-flop under the control of clock CK supplied to one input terminal of this gate, and an inverter I.sub.101 that inverts clock CK and supplies it to the other input terminal of the flip-flop.

To increase the current driving capacity of the data latch, for example, an inverter buffer I.sub.102 is provided as an output buffer as shown FIG. 1B. In the FIG. 1B data latch circuit with the output buffer, data taken in on clock has to pass through three stages of gate G.sub.101, gate G.sub.102, and inverter buffer I.sub.102 before it reaches the output terminal. This delays the data transfer between the input and output in the data latch circuit.

FIG. 1C shows another conventional flip-flop circuit, which is composed of NOR gates G.sub.101 and G.sub.102 constituting a flip-flop stage, AND gates G.sub.501 and G.sub.502 serving as input gates, and inverter buffers I.sub.103 and I.sub.104 serving as output buffers. Like the FIG. 1B data latch circuit, this flip-flop circuit also has a data delay due to three gate stages. Data delay will be explained, referring to the timing chart in FIG. 2. Assume that while data output Q is in the "1" state and the inverse data output of Q, /Q is in the "0" state, data consisting of A="0" and /A="1" is supplied. Here, to cause the input data to appear at the output Q, it is necessary for data /A to cause the output node N.sub.102 of NOR gate G.sub.102 to change from "1" to "0", which then causes the output node N.sub.101 of NOR gate G.sub.101 to change from "0" to "1", thereby changing the output of inverter buffer I.sub.103 from "1" to "0". Therefore, data must pass through three gates, NOR gates G.sub.102 and G.sub.101 , and inverter buffer I.sub.103.

The same is true for D flip-flop circuits and the slave stage of master-slave flip-flop circuits.

As noted above, in various types of conventional flip-flop and data latch circuits, there is a delay introduced by three stages of gates from when data is supplied to the flip-flop stage and when it appears at the output terminal of the output buffer. Such a delay has been an obstacle to faster data processing.

For technical literature related to the present invention, reference may be made to Steven I. Long et al., "High Speed GaAs Integrated Circuits," Proceeding of The IEEE, Vol. 70, No. 1, January 1982, pp. 20-30 and Y. Kamatani et al.,"DIVIDE BY 128/129 5 mW 400 MHz BAND GaAs PRESCALER IC," IEEE, 1985, GaAs IC Symposium, pp. 179-182.

SUMMARY OF THE INVENTION

The object of the present invention is to provide an improved semiconductor integrated circuit, particularly a flip-flop-based semiconductor integrated circuit capable of high-speed operation.

The foregoing object is accomplished by providing a semiconductor integrated circuit comprising: a flip-flop having input terminal means and output terminal means; at least one input gate means having output terminal means connected to the input terminal means, which supplies data to this input terminal under the control of clock; and at least one output buffer means the input terminal means of which is connected to the output terminal means of the flip-flop to receive the output signal of the flip-flop and which is connected to the output terminal means of the input gate means to receive the data from the input gate means to provide an advance read function.

With this configuration, the output buffer is provided with an advance read function, thereby eliminating a delay due to two stages of gates of the flip-flop in transferring data to the output terminal. This approach has no adverse effect on the data retaining function of the flip-flop stage. Consequently, the present invention provides various types of flip-flop circuits and data latch circuits with very small data delays.

In this way, providing the output buffer with an advance read function eliminates the adverse effects of the internal delays in various types of flip-flop circuits and data latch circuits, which helps make semiconductor integrated circuits operate faster.

Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate presently preferred embodiments of the invention, and together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.

FIGS. 1A to 1C are circuit diagrams for various types of conventional semiconductor integrated circuits;

FIG. 2 is a timing chart for explaining the operation of the flip-flop of FIG. 1C;

FIG. 3 is a block diagram for a first embodiment of the RS flip-flop having an input gate according to the present invention;

FIG. 4 is a circuit diagram for the flip-flop circuit of FIG. 3;

FIG. 5 is a timing chart for explaining the operation of the flip-flop of FIG. 4;

FIG. 6 is a circuit diagram for a modification of the flip-flop of FIG. 4;

FIG. 7 is a block diagram for a second embodiment of the RS flip-flop having an input gate according to the present invention;

FIG. 8 is a circuit diagram for the flip-flop circuit of FIG. 7;

FIGS. 9A to 9C are circuit diagrams for the composite gates of FIG. 8;

FIG. 10 is a block diagram for a first embodiment of the data latch circuit according to the present invention;

FIG. 11 is a block diagram for a second embodiment of the data latch circuit according to the present invention;

FIG. 12 is a circuit diagram for a third embodiment of the data latch circuit according to the present invention;

FIG. 13 is a circuit diagram for a fourth embodiment of the data latch circuit according to the present invention;

FIG. 14 is a circuit diagram for a fifth embodiment of the data latch circuit according to the present invention;

FIG. 15 is a circuit diagram for a sixth embodiment of the data latch circuit according to the present invention;

FIG. 16 is a circuit diagram for a seventh embodiment of the data latch circuit according to the present invention;

FIG. 17 is a circuit diagram for a first embodiment of the master-slave flip-flop according to the present invention;

FIG. 18 is a circuit diagram for a second embodiment of the master-slave flip-flop according to the present invention;

FIG. 19 is a circuit diagram for a third embodiment of the master-slave flip-flop according to the present invention;

FIG. 20 is a circuit diagram for a fourth embodiment of the master-slave flip-flop according to the present invention; and

FIG. 21 is a circuit diagram for an embodiment of the D flip-flop according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the accompanying drawings, embodiments of the present invention will be explained.

FIG. 3 is a block diagram for a first embodiment of the RS flip-flop circuit having an input gate according to the present invention. The set input terminal S and reset input terminal R of an RS flip-flop 100 are provided respectively with input gates 200A and 200B, which transfer input data under the control of clock CK. The set output terminal Q and reset output terminal /Q are provided with output buffers 300B and 300A, respectively. The output buffer 300B is supplied with the data from the set output terminal Q and the data supplied to the set input terminal S. That is, the data to the set input terminal S is supplied to the output buffer 300B prior being transferred through the flip-flop 100, to provide the buffer with an advance read function. Similarly, the output buffer 300A, like the output buffer 300B, is supplied with the data from the reset output terminal /Q and the data supplied to the reset input terminal R.

FIG. 4 is a circuit diagram for the flip-flop circuit of FIG. 3. The RS flip-flop 100 is made up of two NOR gates G.sub.101 and G.sub.102. The input gates 200A and 200B are composed of NOR gates G.sub.201 and G.sub.202, respectively. The output buffer 300A and 300B are composed of NOR gates G.sub.301 and G.sub.302. One NOR gate G.sub.301 of the output buffer stage is connected to the output node N.sub.3 of the flip-flop stage and the input node N.sub.2. The other NOR gate G.sub.302 of the output buffer stage is connected to the output node N.sub.4 of the flip-flop stage and the input node N.sub.1.

FIG. 5 is a timing chart for explaining the operation of the flip-flop circuit of FIG. 4. It is assumed that in the initial state, clock CK is a "1", data A is a "038 , data /A is a "1", nodes N.sub.1 and N.sub.2 are a "038 , N.sub.3 is a "1", N.sub.4 is a "038 , output Q.sub.1 is a "1", and output /Q.sub.1 is a "0". The change of clock CK from "1" to "0" causes node N.sub.1 to change from "0" to "1". This change at node N.sub.1 then causes the voltage at the output node N.sub.3 of NOR gate G.sub.101 to fall. This falling voltage at the output node N.sub.3 in turn causes the voltage at the output node N.sub.4 of NOR gate G.sub.102 to rise. In conventional output buffers without an advance read function, as shown by broken lines in FIG. 5, as a result of the rising signal from the output node N.sub.4, the output Q.sub.1 of NOR gate G.sub.302 of the output buffer stage goes to "0". In the present embodiment, however, as shown by solid lines, a rise in the voltage at input node N.sub.1 is supplied directly to NOR gate G.sub.302 of the output buffer stage, which causes the output Q.sub.1 to fall. Therefore, the final output Q.sub.1 ="0" can be obtained without introducing a delay due to two NOR gates G.sub.101 and G.sub.102 constituting the RS flip-flop circuit 100. The same is true in a case where the input data of A="1" and /A="0" is taken in on clock CK and retained. Here, the final output /Q.sub.1 ="0" is obtained without a delay due to two NOR gates found in conventional circuits.

FIG. 6 is a circuit diagram for a modification of the flip-flop circuit of FIG. 4. In this circuit, AND gates G.sub.501 and G.sub.502 replace the NOR gates G.sub.201 and G.sub.202 constituting the input gate of FIG. 4. The AND gate G.sub.501 and G.sub.502 may be such as source-follower AND gates.

FIG. 7 is a block diagram for a second embodiment of the RS flip-flop circuit having an input gate according to the present invention. In this embodiment, in addition to the input gates 200A and 200B for transferring data to the RS flip-flop 100, input gates 200C and 200D are provided to give the output buffers 300A and 300B an advance read function. In this embodiment, the composite gate arrangement of the input gates 200A and 200B and RS flip-flop 100 is useful particularly in cases where the set input terminal S and reset input terminal R cannot be connected directly to the output buffers 300B and 300A.

FIG. 8 is a circuit diagram for the RS flip-flop circuit of FIG. 7. In this circuit, NOR gates G.sub.101 and G.sub.102 constitute the RS flip-flop circuit 100. In the input gates 200A and 200B, AND gates G.sub.503 and G.sub.504 are combined with NOR gates G.sub.101 and G.sub.102, respectively, to form composite gates. AND gates G.sub.505 and G.sub.506, which provide an advance read function for NOR gates G.sub.301 and G.sub.302 constituting the output buffers 300A and 300B, correspond to the input gates 200C and 200D, respectively. In this way, the output buffer section is also constructed to form a composite gate arrangement of AND and NOR elements.

Examples of the AND-to-NOR composite gate arrangement of FIG. 8 are shown in FIG. 9A to 9C. FIG. 9A illustrates an equivalent circuit of gate level, FIG. 9B shows a circuit diagram for the FIG. 9A circuit constructed of MESFETs, and FIG. 9C depicts a circuit diagram for FIG. 9A circuit constructed of CMOS circuits.

FIGS. 10 to 16 illustrate embodiments where the present invention is applied to a data latch circuit.

FIG. 10 is a block diagram for a first embodiment of the data latch circuit according to the present invention. A flip-flop 150 for latching data has the data input terminal D, the input terminal for clock CK.sub.2, and the output terminal Q. The data input terminal D is connected to an input gate 200 that transfers input data under the control of clock CK.sub.1. The data output terminal Q is connected to an output buffer 300. In this embodiment, like the above embodiment, the output buffer 300 is provided with an advance read function that allows the input data to be supplied directly to this buffer before the input passing through the data-latch flip-flop 150. Therefore, as with the above embodiment, the present embodiment provides the output without introducing a delay due to two stages of gates of the data-latch flip-flop 150.

FIG. 11 is a block diagram for a second embodiment of the data latch circuit according to the present invention. In this embodiment, another input gate 200B is provided in parallel with the input gate 200A to give the output buffer 300 an advance read function. The present embodiment, like the embodiment explained in FIG. 7, is useful for composite gate arrangements.

FIG. 12 is a block diagram for a third embodiment of the data latch circuit according to the present invention. The data latch circuit of FIG. 12 is made up of a NOR gate G.sub.211 forming the input gate stage 210, NOR gates G.sub.111 and G.sub.112 constituting a flip-flop stage 110, and a NOR gate G.sub.311 forming the output buffer stage 310. The clock CK is supplied directly to the NOR gate G.sub.211 of the input gate stage 210, and at the same time, is supplied via an inverter gate I.sub.111 to the NOR gate G.sub.112 of the flip-flop stage. Unlike ordinary data latch circuits, in the present embodiment, the signal at the output node of the input gate stage 210 is supplied to the NOR gate G.sub.311 of the output buffer 310 to provide an advance read function.

FIG. 13 is a block diagram for a fourth embodiment of the data latch circuit according to the present invention. The data latch circuit of FIG. 13 is composed of a NAND gate G.sub.441 forming the input gate stage 220, NAND gates G.sub.401 and G.sub.402 constituting the flip-flop stage 120, and a NAND gate G.sub.451 forming the output buffer stage 320. The clock CK is supplied directly to the NAND gate G.sub.441 of the input gate stage 220, and at the same time, is supplied via the inverter gate I.sub.111 to the NOR gate G.sub.402 of the flip-flop stage. Unlike ordinary data latch circuits, the present embodiment allows the signal at the output node of the input gate stage 220 to be supplied to the NAND gate G.sub.451 of the output buffer 320 to provide an advance read function.

FIG. 14 is a block diagram for a fifth embodiment of the data latch circuit according to the present invention. In the data latch circuit of FIG. 14, the flip-flop stage 110 is made up of NOR gates G.sub.111 and G.sub.112. The NOR gate G.sub.111 and an AND gate G.sub.511 forming the input gate stage 230 are combined to form an AND-to-NOR composite gate arrangement. The output buffer stage 330 is made up of the NOR gate G.sub.311. The NOR gate G.sub.311 and an AND gate G.sub.512 are combined to form a composite gate arrangement to provide the output buffer 330 with an advance read function.

FIG. 15 is a block diagram for a sixth embodiment of the data latch circuit according to the present invention. In the data latch circuit of FIG. 15, the input gate stage 220 of FIG. 13 is constructed of a CMOS transfer gate 240. The resistor 400 is designed to present enough resistance for the output node of the transfer gate 220 to go to the "1" level only when the transfer gate 240 turns off.

FIG. 16 is a block diagram for a seventh embodiment of the data latch circuit according to the present invention. In the data latch circuit of FIG. 16, the input gate stage 230 of FIG. 14 is constructed of a CMOS transfer gate 240. With this configuration, because the output node of the input gate 230 can be connected to the output buffer, this provides an advance read function without the AND gate G.sub.512 of FIG. 14. The resistor 400 is designed to present enough resistance for the output node of the transfer gate 240 to go to the "0" level only when the transfer gate turns off, and to maintain the node potential.

The data latch circuits shown in FIGS. 10 to 16, like the above-described embodiments, eliminate the effects of internal delay and enable high speed operation.

FIG. 17 is a circuit diagram for a first embodiment of the master-slave flip-flop circuit according to the present invention. The master flip-flop stage 130 is composed of NAND gates G.sub.421 and G.sub.422 constituting a flip-flop and OR gates G.sub.351 and G.sub.352 forming transfer gates, all of which are integrated into an OR-to-NAND composite arrangement. The slave flip-flop stage 140 is composed of NOR gates G.sub.121 and G.sub.122 constituting a flip-flop and AND gates G.sub.521 and G.sub.522 forming transfer gates, all of which are integrated into a NAND-to-NOR composite arrangement. The output buffers 340A and 340B each consist of AND-to-NOR composite gates, into which NOR gates G.sub.321 and G.sub.322 and AND gates G.sub.523 and G.sub.524 for providing an advance read function are integrated, respectively.

In this embodiment, like the preceding embodiment, while data is still in the course of passing through the slave flip-flop stage 140, the AND gates G.sub.523 and G.sub.524 allow a change in the signal at the output node of the master flip-flop stage 130 to appear at the output buffers 340A and 340B as a change in the output, thereby shortening data delay.

FIG. 18 is a circuit diagram for a second embodiment of the master-slave flip-flop circuit according to the present invention. In the master-slave flip-flop circuit of FIG. 18, the master stage is composed of the master flip-flop 110 consisting of NOR gates G.sub.123 and G.sub.124 and a separate transfer gate 500 consisting of NOR gates G.sub.221 and G.sub.222.

FIG. 19 is a circuit diagram for a third embodiment of the master-slave flip-flop circuit according to the present invention. In the master-slave flip-flop circuit of FIG. 19, the master-slave flip-flop circuit of FIG. 18 is modified in that the slave stage is also composed of the flip-flop 150 consisting of NOR gates G.sub.121 and G.sub.122 and a separate transfer gate 510 consisting Of NAND gates G.sub.423 and G.sub.424. Here, the output buffers 310A and 310B consist only of NOR gates G.sub.321 and G.sub.322, respectively. The output nodes of the NAND gates G.sub.423 and G.sub.424 of the transfer gate stage 510 are connected to the output buffers 310B and 310A, respectively, to provide these buffers with an advance read function.

FIG. 20 is a circuit diagram for a fourth embodiment of the master-slave flip-flop circuit according to the present invention. In the master-slave flip-flop circuit of FIG. 20, the NAND gates of the transfer gate stage 510 of the master-slave flip-flop circuit of FIG. 19 is replaced by NOR gates G.sub.125 and G.sub.126, which forms the transfer gate stage 520.

FIG. 21 is an embodiment of the D flip-flop according to the present invention. The input gate stage 240 is composed of NOR gates G.sub.231, G.sub.232, G.sub.234, and G.sub.235, the flip-flop stage 110 is made up of NOR gates G.sub.131 and G.sub.132, and the output buffers 310A and 310B consist of NOR gates G.sub.331 and G.sub.332, respectively. This D flip-flop differs from ordinary D flip-flops in that the output nodes of the input gate stage 240 are connected to the output buffers 310A and 310B to provide these buffers with an advance read function. Consequently, this embodiment also achieves shorter data delay.

Additional advantages and modifications will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details, and representative devices, shown and described herein. Accordingly, various modifications may be without departing from the spirit or scope of the general inventive concept as defined by the appended claims and their equivalents.

Claims

1. A semiconductor integrated circuit comprising:

a flip-flop having input terminals and output terminals;

at least one input gate means having an output terminal coupled with one of said input terminals of said flip-flop, for supplying data to one of said input terminals of said flip-flop under the control of a clock; and

at least one output buffer means having an input terminal which is directly connected only to one of said output terminals of said flip-flop and said output terminal of said input gate means, for receiving an output signal output from said one output terminal of said flip-flop and data directly supplied from one of said input gate means, thereby providing an advance read function.

2. A semiconductor integrated circuit according to claim 1, wherein

said input terminal means of said flip-flop contains a set input terminal and a reset input terminal, and said output terminal means of said flip-flop contains a set output terminal and a reset output terminal;

said input gate means contains a first input gate connected to said set input terminal of said flip-flop and a second input gate connected to said reset terminal of said flip-flop; and

said output buffer means contains a first output buffer with a first and second input terminals and a second output buffer with a first and second input terminals,

said first input terminal of said first output buffer being connected to said set output terminal of said flip-flop that supplies a set signal to said first input terminal of said first output buffer, while said second input terminal of said first output buffer being connected to said output terminal of said second input gate that supplies a signal equivalent to a reset signal input to said reset input terminal of said flip-flop, and

said first input terminal of said second output buffer being connected to said reset output terminal of said flip-flop that supplies a reset signal to said first input terminal of said second output buffer, with said second input terminal of said second output buffer being connected to said output terminal of said first input gate that supplies a signal equivalent to said set signal input to said set input terminal of said flip-flop.

3. A semiconductor integrated circuit according to claim 2, wherein each of said first and second output buffer means is composed of a NOR gate having at least two input terminals.

4. A semiconductor integrated circuit according to claim 1, wherein

said input terminal means of said flip-flop contains a set input terminal and a reset input terminal, and said output terminal means of said flip-flop contains a set output terminal and a reset output terminal;

said input gate means contains a first input gate connected to said set input terminal of said flip-flop, a second input gate connected to said reset terminal of said flip-flop, a third input gate having an output terminal, and fourth input gate having an output terminal; and

said output buffer means contains a first output buffer with a first and second input terminals and a second output buffer with a first and second input terminal,

said first input terminal of said first output buffer being connected to said set output terminal of said flip-flop that supplies a set signal to said first input terminal of said first output buffer, with said second input terminal of said first output buffer being connected to said output terminal of said fourth input gate that supplies a signal equivalent to said reset signal input to said reset input terminal of said flip-flop, and

said first input terminal of said second output buffer being connected to said reset output terminal of said flip-flop that supplies a reset signal to said first input terminal of said second output buffer, with said second input terminal of said second output buffer being connected to said output terminal of said third input gate that supplies a signal equivalent to said set signal input to said set input terminal of said flip-flop.

5. A semiconductor integrated circuit comprising:

a flip-flop having a set input terminal, a reset input terminal, a set output terminal and a reset output terminal;

a first input gate connected to said set input terminal of said flip-flop to supply data to said input terminal of said flip-flop under the control of a first clock;

a second input gate connected to said reset input terminal of said flip-flop to supply data to said input terminal of said flip-flop under the control of a second clock;

a first output buffer connected to said set output terminal of said flip-flop to receive a signal from said output terminal of said flip-flop and also connected to said second input gate to receive a signal input to said reset input terminal of said flip-flop; and

a second output buffer connected to said reset output terminal of said flip-flop to receive a signal from said output terminal of said flip-flop and connected to said first input gate to receive a signal input to said input terminal of said flip-flop.

6. A semiconductor integrated circuit comprising:

a flip-flop having a set input terminal, a reset input terminal, a set output terminal and a reset output terminal;

a first input gate connected to said set input terminal of said flip-flop to supply data to said set input terminal of said flip-flop under the control of a clock;

a second input gate connected to said reset input terminal of said flip-flop to supply data to said reset input terminal of said flip-flop under the control of said clock;

a third input gate that receives the same data as that supplied to said second input gate and supplies a specified data under the control of said clock;

a fourth input gate that receives the same data as that supplied to said first input gate and supplies a specified data under the control of said clock;

a first output buffer connected to said set output terminal of said flip-flop to receive a signal from said output terminal of said flip-flop and also connected to said third input gate to receive a signal equivalent to a signal at said reset input terminal of said flip-flop; and

a second output buffer connected to said reset output terminal of said flip-flop to receive a signal from said output terminal of said flip-flop and connected to said fourth input gate to receive a signal equivalent to a signal at said set input terminal of said flip-flop.

7. A semiconductor integrated circuit comprising:

a flip-flop circuit for latching data with a data input terminal, a data output terminal, and a clock input terminal to which a first clock signal is supplied for holding data;

at least one input gate means connected to said data input terminal of said flip-flop to transfer data to said data input terminal of said flip-flop under the control of a second clock signal; and

output buffer means with a first and second input terminals, said first input terminal of said buffer means being connected to said data output terminal of said flip-flop to receive a signal from said output terminal of said flip-flop, and said second input terminal of said output buffer means being connected to said input gate means to receive a signal equivalent to a signal supplied to said data input terminal of said flip-flop.

8. A semiconductor integrated circuit according to claim 7, wherein said flip-flop is composed of two NOR circuits, said input gate means is composed of one NOR circuit, and said output buffer means is composed of one NOR circuit.

9. A semiconductor integrated circuit according to claim 7, wherein said flip-flop is composed of two NAND circuits, said input gate means is composed of one NAND circuit, and said output buffer means is composed of one NAND circuit.

10. A semiconductor integrated circuit according to claim 7, wherein said flip-flop is composed of two NAND circuits, said output buffer means is composed of one NAND circuit, and said input gate means is composed of a CMOS transfer gate.

11. A semiconductor integrated circuit according to claim 7, wherein said flip-flop is composed of two NOR circuits, said output buffer means is composed of one NOR circuit, and said input gate means is composed of a CMOS transfer gate.

12. A semiconductor integrated circuit according to claim 7, wherein said input gate means includes a first input gate connected to said data input terminal of said flip-flop to transfer data to said input terminal of said flip-flop under the control of said second clock, and a second input gate connected to said output buffer means to transfer data to said buffer means under the control of a third clock.

13. A semiconductor integrated circuit according to claim 12, wherein said flip-flop is composed of two NOR circuits, said output buffer means is composed of one NOR circuit, and said input gate means is composed of one AND circuit.