A Novel Capacitive Detection Scheme With Inherent Self-Calibration

This paper reports a novel capacitive detection method, called the sideband-ratio (SBR) detection, which is robust to variations of such critical parameters as the nominal capacitance, frequency, and amplitude of the probing voltage and gain of the transimpedance amplifier. The approach constructively utilizes the inherent nonlinearity of parallel-plate sense capacitors in order to measure the amplitude of sinusoidal motion. In the case of parallel-plate detection signal, multiple harmonics exist and each carry information about the amplitude of mechanical motion. The SBR method robustly extracts the amplitude of motion from the ratio of multiple sidebands. This paper presents theoretical background and analysis of this nonlinear measurement method. A real-time measurement algorithm is implemented in software and simulated. Feasibility of the developed approach is demonstrated experimentally.