Patent ID: 8384400

Claim:
A capacitance measurement circuit, comprising: an operation amplifier having a first input terminal, a second input terminal and an output terminal; a reference capacitor having a first terminal coupled to the first input terminal of the operation amplifier and a second terminal selectively coupled to a first reference voltage or a second reference voltage; a sensor capacitor having a first terminal coupled to the second input terminal of the operation amplifier and a second terminal selectively coupled to the first reference voltage or the second reference voltage; an approximation unit having an output terminal and an input terminal coupled to the output terminal of the operation amplifier; a conversion unit having an output terminal and an input terminal coupled to the output terminal of the approximation unit; a coupling capacitor having a first terminal coupled to the first input terminal or the second input terminal of the operation amplifier and a second terminal coupled to the output terminal of the conversion unit; a first switch having a first terminal coupled to the second terminal of the reference capacitor and a second terminal coupled to the first reference voltage or the second reference voltage; a second switch having a first terminal coupled to the second terminal of the sensor capacitor and a second terminal coupled to the first reference voltage or the second reference voltage; a third switch having a first terminal coupled to the second input terminal of the operation amplifier and a second terminal selectively coupled to the second reference voltage; a fourth switch having a first terminal coupled to the first input terminal of the operation amplifier and a second terminal selectively coupled to the second reference voltage; a first parasitic capacitor having a first terminal coupled to the first input terminal of the operation amplifier and a second terminal coupled to the second reference voltage; a second parasitic capacitor having a first terminal coupled to the second input terminal of the operation amplifier and a second terminal coupled to the second reference voltage; and a match coupling capacitor having a first terminal coupled to the first input terminal or the second input terminal of the operation amplifier and a second terminal coupled to the second reference voltage.