Patent ID: 7267002
Filing Date: 2007-09-11
Classification: G01D,G01N

Abstract:
1. A capacitance type physical quantity detector comprising: a sensor unit of which the capacitance varies depending upon a change in the physical quantity; and a C-V converter unit of the switched capacitor constitution which converts a change in the capacitance of said sensor unit into a voltage, wherein said C-V converter unit includes an operational amplifier, a feedback capacitor provided between an input terminal and an output terminal of said operational amplifier, and switching means connected in parallel with said feedback capacitor, said capacitance type physical quantity detector further includes a reference voltage-generating circuit for applying a reference voltage to the non-inverted input terminal of said operational amplifier, and a drive voltage-generating circuit for applying a drive voltage to said sensor unit, at least any one of the feedback capacitance of said feedback capacitor, the reference voltage formed by said reference voltage-generating circuit or the drive voltage formed by said drive voltage-generating circuit so varies depending upon the temperature as to correct the temperature characteristics of said sensor unit, said feedback capacitor is constituted by interposing a capacitance-adjusting film having predetermined temperature characteristics between a pair of feedback electrodes that are arranged facing each other and being spaced apart, said sensor unit includes a pair of detecting electrodes arranged on the same plane of a substrate facing each other and being spaced apart, a moisture-sensitive film having temperature characteristics provided on the substrate so as to cover said pair of detecting electrodes and to cover the distance between said pair of detecting electrodes, and a pair of reference electrodes arranged on the same plane of said substrate facing each other and being spaced apart, and said feedback capacitor includes a pair of said feedback electrodes arranged on the same plane of said substrate facing each other and being spaced apart, and said capacitance-adjusting film provided on said substrate so as to cover said pair of feedback electrodes and to cover the distance between said pair of feedback electrodes.