Patent ID: 8800371

Claim:
An electrostatic force generator, comprising: a capacitive module including a first capacitor and a second capacitor; a differential transformer configured to generate a differential signal in response to a capacitive difference between the first capacitor and the second capacitor; a proportional-integral-derivative (PID) controller configured to generate a first alternative current (AC) signal in response to the differential signal, and to apply the first AC signal to the first capacitor to generate an electrostatic force for achieving a capacitive balance between the first capacitor and the second capacitor; a resonant capacitive-inductive bridge module including a first loop, a second loop, a first variable capacitor and a second variable capacitor, wherein the differential transformer includes two primary windings and a secondary winding, the two primary windings are in the first loop and the second loop, respectively; the first variable capacitor is configured to adjust a total capacitance in the first loop, and the second variable capacitor is configured to adjust a total capacitance in the second loop; a lock-in amplifier module configured to generate an output signal V x in response to the differential signal, wherein the differential signal is demodulated at a RF excitation frequency; and a third variable capacitor configured to set a resonant frequency of the resonant capacitive-inductive bridge module to be equal to the RF excitation frequency.