US Patent 7479832 Differential amplifying system

A differential amplifying system has a differential amplifier for amplifying a voltage signal inputted from an input terminal and outputting the amplified voltage signal through an output terminal; an amplitude detection circuit for detecting an amplitude of said voltage signal inputted to said differential amplifier and outputting a detected current corresponding to the amplitude; a compensation circuit having: a current mirror circuit for outputting a compensating current at a desired mirror ratio for an input of said detected current; and a feedback circuit for changing a mirror ratio of said current mirror circuit in order to control a magnitude of the compensating current according to an amplitude of the voltage signal detected by said amplitude detection circuit; and a bias circuit for supplying bias voltage to said differential amplifier in order to add a bias value to inputted said voltage signal based on the magnitude of said compensating current.