Semiconductor integrated circuit

#1. Field of the Invention

#The present invention relates to a semiconductor integrated circuit, and in particular to a circuit having an input buffer, an internal circuit and an output buffer, in which a power supply voltage supplied to the internal circuit is different from power supply voltages supplied to the input and output buffers.

#2. Related Art

#FIG. 1 shows a structural view of semiconductor integrated circuit according to a first embodiment of the present invention.

#FIG. 2 is a view showing another structure of the semiconductor integrated circuit of the first embodiment.

#FIG. 3 is a structural view of the semiconductor integrated circuit according to a second embodiment of the present invention.

#Hereinafter, embodiments of semiconductor integrated circuit according to the present invention will be described in detail with reference to the attached drawings. According to research and analysis, it is found that a threshold of input signal of input circuit varies greatly when data is outputted. Further, it is found that such phenomenon occurs because a power supply of the input circuit is the same as that of the output circuit in spite of a low power supply voltage and thus the input circuit is affected by a noise from the output circuit. Taking such points in consideration, structures shown in the following embodiments are devised.

#First Embodiment.

#FIG. 1 shows a structure of semiconductor integrated circuit of the present invention. The semiconductor integrated circuit includes an input circuit 11 including an input buffer for receiving a data signal from outside, an internal circuit 15 which carries out a processing corresponding to a predetermined function of the semiconductor integrated circuit and an output circuit 13 including an output buffer for generating from the data signal received from the internal circuit 15 a signal to be outputted to a subsequent circuit. The semiconductor integrated circuit also includes step-down circuits 21 and 23.