Patent ID: 7640806

Claim:
A capacitive physical quantity sensor comprising: a sensor element including a movable electrode displaceable in accordance with a variation of a physical quantity, and first and second fixed electrodes facing the movable electrode, wherein a first periodic carrier wave voltage is applied to the first fixed electrode and a second periodic carrier wave voltage is applied to the second fixed electrode, the first and second periodic carrier wave voltages are inverse to each other; and a detecting circuit including a capacitance-voltage conversion circuit, into which an input potential corresponding to a variation of a capacitance between the movable electrode and the first and second fixed electrodes is input, and from which a voltage signal corresponding to the variation of the capacitance is output, wherein the detecting circuit further includes a sample-hold circuit for sampling and holding the voltage signal, the sample-hold circuit includes a switch for switching the sampling and the holding, the switch includes a P-channel MOS transistor and a N-channel MOS transistor, which are connected in parallel to each other, and the P-channel MOS transistor and the N-channel MOS transistor have a back gate potential, which is approximately equal to an average voltage of the first periodic carrier wave voltage and the second periodic carrier wave voltage.