Patent ID: 9110114
Filing Date: 2015-08-18
Classification: G01D,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 first feedback capacitors, a second feedback capacitor, 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 first feedback capacitors have first ends respectively connected to the detection terminals and have second ends connected together, the second feedback capacitor has a first end connected to the second ends of the first feedback capacitors, the voltage switch circuit applies the predetermined voltage or a first preset voltage to the second ends of the first feedback capacitors to charge the first feedback capacitors during the first level of the drive signal, the first preset voltage has a voltage value existing in a voltage direction in which the second level exists relative to the first level with respect to the predetermined voltage, the voltage switch circuit applies a second preset voltage to the second ends of the first feedback capacitors and applies the predetermined voltage to a second end of the second feedback capacitor to charge the second feedback capacitor during the second level of the drive signal, and then applies the feedback voltage to the second end of the second feedback capacitor instead of the application of the second preset voltage and the predetermined voltage, and the second preset voltage has a voltage value existing in a voltage direction in which the first level exists relative to the second level with respect to the predetermined voltage.