A high dynamic range wideband CMOS phase angle detector for bioimpedance spectroscopy

A power-efficient wideband zero-crossing phase angle detector for bioelectrical impedance measurement is described. The detector consists of a pair of instrumentation amplifiers, two identical limiting amplifiers, and digital circuitry that compensates for offset errors introduced by the analog blocks. Designed in a 0.35-μm CMOS process and at a 2-V supply, the proposed phase detector measures the phase difference between two signals with amplitudes in the range of 25 μV to 25 mV over a frequency interval from 1 kHz to 1 MHz, with a typical error of less than 0.4° at the highest frequencies.