A 30-MHz Wideband 92.7-dB SNR 99.6% Accurate Bioimpedance Spectroscopy IC Using Time-to-Digital Demodulation and Co-Prime Delay-Locked Sampling

The impedance of biological tissues provides valuable physiological information up to tens of megahertz. Conventional bioimpedance readout methods face significant tradeoffs between power consumption and measurement accuracy at higher frequencies. To address these limitations, this article presents a 30-MHz wideband bioimpedance spectroscopy integrated circuit (IC) using time-to-digital (T–D) demodulation. To provide high-accuracy measurement at high frequencies, a novel co-prime delay-locked sampling method is proposed, achieving a 21.6-GHz equivalent sampling rate (with a temporal resolution of 46.3 ps) using a 240-MHz primary clock frequency. To achieve the high-precision delay generation required, a new delay-locked loop (DLL) topology based on a compact phase comparator is introduced. Using these techniques, the IC achieves an average 92.7-dB SNR, 99.6% accuracy with a 0.39% magnitude error and a 0.57° phase error, and consumes 3.18 mW of power at 30 MHz. This IC provides at least three times the bandwidth of prior work while consuming three times less power compared to other megahertz systems.