Adaptive Cancellation of Parasitic Coupling

Abstract

This paper reports a signal processing technique that adaptively identifies a finite-impulse-response (FIR) model of the parasitic coupling between the input ports and the output ports of a microelectromechanical resonator. The identified model is used as a feedforward filter to reduce the severity of the parasitic coupling by subtracting the filtered input port signal from the resonator’s output port signal. The compensated signals reveal the resonator’s motional response, which was previously obscured by the coupling, so that modal frequency and quality factor measurements can be performed. The experimental results also show that the adaptive filter tracks changes in the parasitic coupling during turn-on and warm-up periods. More than 30 dB of suppression of the parasitic coupling is achieved over a broad frequency band. The adaptive FIR filter is implemented on the signal processing equipment that is used to gather resonator stimulus-response data so no modifications to the resonator or its buffer electronics are required.