Design and verification of reconfigurable finite impulse response filters and its application to bio-impedance measurement system

Abstract

This dissertation proposes sinusoidal signal generators (SSGs) and polar demodulators for bio-impedance measurement system which supports a frequency range from 1 kHz to 2048 kHz. The proposed SSGs use reconfigurable finite impulse response (FIR) filters to achieve high linearity. Design and verification of various FIR filters were performed to determine the most suitable FIR filter for the proposed SSGs. In particular, an SSG based on a constant-gain FIR filter consumes 5.1 mW and achieves a total harmonic distortion less than 0.2% using a simple digital-to-analog converter and a low-speed clock. Two self-sampling schemes and a reconfigurable time-to-digital converter (TDC) are proposed for the low-power design of polar demodulators. These self-sampling schemes extract the magnitude of the impedance by reusing signals in the phase measurement circuits. The TDC is designed to handle a wide input-time range and to improve the time resolution without increasing the clock speed.