Patent ID: 9182433
Filing Date: 2015-11-10
Classification: G01N,G01R

Abstract:
1. A detection circuit for a capacitive sensor including a pair of sense capacitors with capacitances having a difference responsive to a physical quantity, first ends of the sense capacitors being connected together to provide a common terminal, second ends of the sense capacitors being configured to provide separate detection terminals, the detection circuit comprising: a drive signal generation circuit capable of generating and applying a drive signal to the common terminal, the drive signal varying between a first level and a second level; a fully differential sense amplifier having inverting and non-inverting input terminals respectively connected to the detection terminals, the sense amplifier being capable of outputting a differential voltage according to the difference between the capacitances of the sense capacitors; and a common-mode voltage control circuit capable of controlling an input common-mode voltage of the sense amplifier to a predetermined voltage, wherein the common-mode voltage control circuit includes a feedback amplifier, a pair of feedback capacitors, and a voltage switch circuit, the feedback amplifier outputs a feedback voltage according to a difference between the input common-mode voltage and the predetermined voltage, the feedback capacitors have first ends respectively connected to the detection terminals and have second ends connected together, the voltage switch circuit applies a preset voltage to the second ends of the feedback capacitors to charge the feedback capacitors during the first level of the drive signal and applies the feedback voltage instead of the preset voltage to the second ends of the feedback capacitors during the second level of the drive signal, and the preset voltage has a voltage value between the predetermined voltage and a limit voltage outputtable by the feedback amplifier in a voltage direction in which the second level exists relative to the first level.