Patent ID: 7868623

Claim:
A detection circuit that detects an alternating current signal from a physical quantity transducer that converts a physical quantity into an electrical signal, the detection circuit comprising: a detection terminal, the alternating current signal from the physical quantity transducer being input to the detection terminal; a detection current/voltage conversion amplifier circuit that includes a feedback resistor and converts the alternating current signal input through the detection terminal into a voltage signal; an evaluation terminal that supplies an evaluation voltage signal to the detection current/voltage conversion amplifier circuit; an input resistor provided in a signal path that connects the evaluation terminal and an input node of the detection current/voltage conversion amplifier circuit, the input resistor having a given resistance ratio with respect to the feedback resistor; and a switch circuit of the detection circuit provided in the signal path that connects the evaluation terminal and the input node of the detection current/voltage conversion amplifier circuit, the switch circuit of the detection circuit electrically connecting the evaluation terminal and the input node of the detection current/voltage conversion amplifier circuit when the evaluation voltage signal is input to the evaluation terminal, and electrically disconnecting the evaluation terminal from the input node of the detection current/voltage conversion amplifier circuit when the alternating current signal is input to the detection terminal.