IEEE Trans Biomed Circuits Syst. 2020 Oct;14(5):997-1007. doi: 10.1109/TBCAS.2020.3012057. Epub 2020 Jul 27.
Bioimpedance analysis is a noninvasive and inexpensive technology used to investigate the electrical properties of biological tissues. The analysis requires demodulation to extract the real and imaginary parts of the impedance. Conventional systems use complex architectures such as I-Q demodulation. In this paper, a very simple alternative time-to-digital demodulation method or 'time stamp' is proposed. It employs only three comparators to identify or stamp in the time domain, the crossing points of the excitation signal, and the measured signal. In a CMOS proof of concept design, the accuracy of impedance magnitude and phase is 97.06% and 98.81% respectively over a bandwidth of 10 kHz to 500 kHz. The effect of fractional-N synthesis is analysed for the counter-based zero crossing phase detector obtaining a finer phase resolution (0.51˚ at 500 kHz) using a counter clock frequency ( f = 12.5 MHz). Because of its circuit simplicity and ease of transmitting the time stamps, the method is very suited to implantable devices requiring low area and power consumption.
生物阻抗分析是一种用于研究生物组织电特性的非侵入性和低成本技术。该分析需要解调以提取阻抗的实部和虚部。传统系统使用复杂的架构，如 I-Q 解调。在本文中，提出了一种非常简单的替代时间数字解调方法或“时间戳”。它仅使用三个比较器来在时域中识别或标记激励信号和测量信号的交点。在 CMOS 概念验证设计中，在 10 kHz 至 500 kHz 的带宽内，阻抗幅度和相位的精度分别为 97.06%和 98.81%。基于计数器的过零相位检波器分析了分数 N 合成的影响，通过计数器时钟频率（f = 12.5 MHz）获得了更精细的相位分辨率（500 kHz 时为 0.51˚）。由于其电路简单且易于传输时间戳，该方法非常适合需要低面积和功耗的植入式设备。
