Variable gain semiconductor circuit

Abstract

Disclosed is a variable gain semiconductor circuit enjoying a low insertion loss, good distortion characteristic, and large variable gain range. The variable gain semiconductor circuit comprises: a first kind of variable gain circuit that inputs an input signal and changes a gain on the basis of a first control signal; a second kind of variable gain circuit, installed in a stage succeeding the first kind of variable gain circuit, for changing a gain on the basis of a second control signal; and a control signal producing unit for producing the first and second control signals using an attenuation value control signal. When the attenuation value control signal falls within one of two variation ranges instructing a large gain, the control signal producing unit produces the first and second control signals so that the first kind of variable gain circuit decreases a gain according to the variation of the attenuation value control signal, and the second kind of variable gain circuit produces a constant gain. When the attenuation value control signal falls within the other variation range instructing a small gain, the control signal producing unit produces the first and second control signals so that a decrease in gain produced by the first kind of variable gain circuit is saturated and the gain remains unchanged, and a gain produced by the second kind of variable gain circuit decreases according to the variation of the attenuation value control signal.

Dependencies are inferred from the claim text.