A MOVING WINDOW FILTER BASED FREQUENCY ESTIMATOR FOR CAPACITANCE MEASUREMENT

Abstract

A frequency estimation technique is proposed based on moving window filter (MWF) for measurement of unknown capacitance. The proposed frequency locked loop (FLL) utilizes the flat frequency response characteristics of the moving window filter (MWF) in closed loop and adaptive sampling pulse adjustment for capacitance measurement. An operational amplifier (op-amp) based relaxation oscillator generates a square wave whose - fundamental sine wave is extracted by MWF. Then, the fundamental sine wave is tracked by the FLL to estimate its frequency which is inversely proportional to the unknown capacitance. The FLL employs another MWF to track the center frequency and its variation due to capacitance. The MWF offers almost flat frequency response around the center frequency in closed loop. However, the small magnitude and phase errors observed in the flat frequency response had been corrected by adjusting the sampling pulses adaptively. The proposed scheme is simulated and tested by implementing in a field programmable gate array (FPCA). Simulation results and experimental investigation demonstrates the capabilities of the scheme for accurate frequency estimation in the range of 10 33 kHz and capacitance measurement in the range of 50 - 213 pF The same algorithm has been utilized to extend the frequency estimation range to 3.986-- 78.125 kHz using multiple MWF-FLLs and its accuracy is verified through simulation results.