Patent ID: 7652486
Filing Date: 2010-01-26
Classification: G01P,G01R

Abstract:
1. A capacitance detection circuit for detecting a capacitance change value of a sensor element, the capacitance detection circuit comprising: a C-V circuit, connected to the sensor element, for amplifying the capacitance change value of the sensor element by a predetermined gain based on a reference voltage to generate a detection signal; and a voltage compensation circuit, connected to the C-V circuit, for supplying the reference voltage to the C-V circuit, wherein when the reference voltage fluctuates by a predetermined deviation amount, the voltage compensation circuit reduces the gain relative to the deviation amount; wherein the C-V circuit includes: the sensor element includes: wherein the sensor element and feedback capacitor set a first load capacitance applied to the first input terminal of the operational amplifier; and the voltage compensation circuit includes a plurality of balance capacitors that set a second load capacitance, which is applied to the second input terminal of the operational amplifier, to substantially the same value as the first load capacitance; wherein the plurality of balance capacitors include: a first balance capacitor having a first electrode, which is connected to the second input terminal of the operational amplifier, and a second electrode, which receives the first drive signal; a second balance capacitor having a first electrode, which is connected to the first electrode of the first balance capacitor, and a second electrode, which receives the second drive signal; a third balance capacitor having a first electrode, which is connected to the second input terminal of the operational amplifier, and a second electrode, which receives the reference voltage; and a fourth balance capacitor having a first electrode, which is connected to the second input terminal of the operational amplifier, and a second electrode, which is connected to the second electrode of the third balance capacitor.