Circuit and method for sensing a differential capacitance

摘要

A circuit for sensing a differential capacitance includes a charge-storing circuit to generate a first output voltage and a second output voltage related to capacitances at two terminals of the differential capacitance, respectively, an operational amplifier to amplify the difference between the first and second output voltages to generate a sensing value, a first sampling capacitor having one terminal connected to the negative input terminal and the other terminal receiving the first or second output voltage, and a second sampling capacitor having one terminal connected to the negative input terminal and the other terminal switched to the output terminal of the operational amplifier. The second sampling capacitor stores a non-ideal error value to offset the non-ideal effect of the operational amplifier imparted on the sensing value.

主权项

1. A method for sensing a differential capacitance, comprising steps of:
A.) switching switches to make two terminals of the differential capacitance get connected to a high-voltage source or a low-voltage source or perform charge transfer; B.) storing charges transferred from the differential capacitance to generate a first output voltage and a second output voltage related to capacitances at the two terminals of the differential capacitance; C.) simultaneously resetting a first sampling capacitor and storing a non-ideal error value at a negative input terminal of an operational amplifier into a second sampling capacitor; D.) sampling the first output voltage with the first sampling capacitor; E.) sampling the second output voltage with the first sampling capacitor; and F.) connecting the second sampling capacitor between the negative input terminal and an output terminal of the operational amplifier to generate a sensing value related to a difference between the first and second output voltages.