SWITCHED CAPACITOR CIRCUIT

摘要

PROBLEM TO BE SOLVED: To suppress a drift of an input common mode voltage of a fully differential operational amplifier due to a variation in a common mode voltage of input signal voltages.SOLUTION: In a sampling period, a control circuit 16 turns switches S2p, S3p, S8p off, switches S1p, S4p, S5p, S9p on, and switches S6p, S7p to a signal voltage input side to set a charge depending on a signal voltage Vinp in capacitors Cs10p, Cs11p, Cfp. In a subsequent feedback period, the switches S2p, S3p, S8p are turned on, the switches S1p, S4p, S5p, S9p are turned off, and the switches S6p, S7p are set to select a reference voltage Vrefp or Vrefm in accordance with a differential voltageΔV between a common mode voltage of signal voltages Vinp, Vinm and a common voltage Vcom. An inverting signal input terminal side is similarly controlled. The signal voltages Vinp, Vinm can be amplified with an input common mode voltage Vx of an operational amplifier 15 kept within a predetermined voltage range providing a high amplification factor of the operational amplifier 15.