A CMOS low-power polar demodulator for electrical bioimpedance spectroscopy using adaptive self-sampling schemes

A CMOS integrated low-power polar demodulator for electrical bioimpedance spectroscopy is proposed. This polar demodulator extracts magnitude and phase of tissue's impedance. Two adaptive self-sampling schemes, namely zero-time sampling (ZTS) and peak-time sampling (PTS), are proposed to efficiently extract the magnitude of impedance. Since ZTS scheme reuses clock signals used in the XOR-based phase-extracting circuit, low-power consumption is achieved. When ZTS scheme is used, magnitude error increases as frequency of the injected sinusoidal signal increases. Instead of ZTS scheme, PTS scheme is used when the signal above 100 kHz is injected. Targeting 1-kHz to 2.048-MHz frequency range, the proposed demodulator designed in a 0.25-im CMOS process consumes 10.3 mW at its maximum with magnitude and phase errors of 1.0% and 1.3°, respectively.