Patent ID: 7343802

Claim:
A dynamic-quantity sensor comprising: a piezoelectric-vibrator series circuit including two piezoelectric vibrators to which stresses induced by a dynamic quantity are applied in opposite directions; a Colpitts oscillator circuit including an amplifier circuit and a load impedance circuit connected to the piezoelectric-vibrator series circuit; and a phase-difference-to-voltage converter circuit arranged to convert a phase difference between a voltage at a series node between the two piezoelectric vibrators of the piezoelectric-vibrator series circuit and an output voltage of the oscillator circuit into a voltage; wherein the oscillator circuit includes a first capacitor connected between a first end of the piezoelectric-vibrator series circuit and a ground, a second capacitor connected between a second end of the piezoelectric-vibrator series circuit and the ground, an input portion of the amplifier circuit connected to the first end of the piezoelectric-vibrator series circuit, and an output-side resistor connected between an output portion of the amplifier circuit and the second end of the piezoelectric-vibrator series circuit; and an impedance of the output-side resistor is greater than an output impedance of the amplifier circuit, and the impedance of the output-side resistor and a capacitance of the second capacitor are set such that the product of the impedance of the output-side resistor and the capacitance of the second capacitor is greater than a value 1/(2πf), where f is an oscillation frequency of the oscillator circuit.