Variable-gain amplifier circuit, offset control method in variable-gain amplifier circuit, radio receiver with variable-gain amplifier circuit, and radio receiving method in radio receiver with variable-gain amplifier

摘要

A variable-gain amplifier circuit has an offset correcting function by which the fluctuation of offset due to the switching of a gain is decreased. In an offset detection mode, an input offset voltage of the variable-gain amplifier circuit is inputted to an offset retaining section, and in a signal amplifying mode, the offset is corrected by subtracting the output of the offset retaining section from an input signal by means of an input section of the variable-gain amplifier circuit. In addition, the variable-gain amplifier circuit can be applied to a radio receiver. The offset produced in a baseband section of a receiver is corrected by the offset correcting function of the variable-gain amplifier circuit, so as to prevent the quality of communication from being deteriorated.