Patent ID: 9664719
Date: 2017-05-30
CPC Classifications: G01D,G01P,G01R,H05K

Claim:
1. A capacitance detection circuit for detecting a small capacitance between a movable electrode and a fixed electrode in a physical quantity sensor, with the movable electrode and the fixed electrode generating a change in capacitance in response to a change in physical quantity, the capacitance detection circuit comprising, at least: a bias voltage generating circuit that generates a bias voltage to be supplied to one of the movable electrode or the fixed electrode; an operational amplifier that has input terminals, with one of the movable electrode or the fixed electrode being input to one of the input terminals and another one of the input terminals being connected to ground; and a printed circuit board on which the physical quantity sensor, the bias voltage generating circuit, and the operational amplifier are mounted, wherein an insulation-secured area on the printed circuit board is configured as a moisture absorption reduction area, the insulation-secured area including at least an electrode connection pad of the physical quantity sensor, an input-side connection pad of the operational amplifier, and connection pads connected to an input side of the operational amplifier, out of connection pads of input-side circuit components connected between the electrode connection pad and the input-side connection pad; and wherein the moisture absorption reduction area forms a resist-applied area that is applied with a resist to cover the insulation-secured area, and a band-like separation area that surrounds the insulation-secured area in such a manner as to separate the resist-applied area from a resist-applied area therearound, the band-like separation area being configured as a non-resist-applied area and as a non-silk-printing area.