Importance

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Abstract

An input-output circuit in which, even if variations in logic threshold voltages occurs, a logic signal can be exactly recognized on the basis of small-amplitude signals supplied. The input-output circuit of the present invention contains a threshold value detecting circuit, an amplifying section used to output a voltage having amplitude center level of a small-amplitude signal, to amplify the small-amplitude signal to a predetermined amplitude level, to convert the small-amplitude signal to a logic signal (rectangular wave) that can be processed by a CMOS internal circuit and to feed the converted signal through an output terminal to the CMOS internal circuit, a constant current circuit used to change amplification factor of the small-amplitude signal inputted, and a feedback amplifier to compare the amplitude center voltage of the small-amplitude signal with a voltage supplied from the threshold value detectt ing circuit and to feedback a voltage to the constant current circuit so that the amplitude center voltage of the signal amplified by the amplifying section is equal to a voltage set by the threshold value detectt ing circuit.

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First Claim