Patent ID: 7397406

Claim:
An A/D conversion circuit with a carrier frequency removing feature, comprising: an A/D converter including a voltage comparator that compares a first signal with a feedback signal and a voltage feedback circuit that produces the feedback signal; a one-input N-output demultiplexer that receives the feedback signal; N integrators each of which calculates the integral of values represented by each of N output signals of the demultiplexer; an N-input one-output multiplexer that receives the output signals of the N respective integrators; a subtractor that produces a difference between an analog signal, which has a signal wave superposed on a carrier wave, and the output signal of the multiplexer; an amplifier that amplifies the output signal of the subtractor to produce the first signal; and a switching control circuit that cyclically switches the input terminals of the multiplexer and the output terminals of the demultiplexer synchronously with the carrier wave.