Patent ID: 7231195

Claim:
A variable gain control circuit for executing automatic-gain-control on a variable gain amplification block composed of a plurality of amplifiers to which gains are discretely set by a programmable-gain-amp method, comprising: level detection means for detecting a current amplifier output level; programmable-gain-amp control data storage means for storing programmable-gain-amp data corresponding to a difference between a current amplifier output level and a predetermined amplifier output level; programmable-gain-amp data generating means for generating programmable-gain-amp data for controlling a gain of said variable gain amplification block on the basis of an output of said programmable-gain-amp control data storage means; direct-current offset cancel storage means for storing beforehand direct-current offset cancel data corresponding to a direct-current offset voltage of an amplifier output which occurs when discrete gain switching of said variable gain amplification block is executed from currently set programmable-gain-amp data to programmable-gain-amp data to be set next; and control means for referencing said direct-current offset cancel storage means on the basis of currently set programmable-gain-amp data and programmable-gain-amp data to be set next to generate corresponding direct-current offset cancel data; and means for converting the generated direct-current offset cancel data into an analog voltage and adds said analog voltage to an amplifier output.