Design and Analysis of Low-Distortion Demodulators for Modulated Sensors

Abstract

System-based demodulators in the form of a Kalman and Lyapunov filter have been demonstrated to significantly outperform traditional demodulators, such as the lock-in amplifier, in bandwidth sensitive applications, for example, high-speed atomic force microscopy. Building on their closed-loop architecture, this paper describes a broader class of high-speed closed-loop demodulators. The generic structure provides greater flexibility to independently control the bandwidth and sensitivity to out-of-band frequencies. A linear time invariant description is derived, which allows the utilization of linear control theory to design the demodulator. Experimental results on a nanopositioner with capacitive sensors demonstrate that the realization of arbitrary demodulator dynamics while achieving excellent noise rejection.