Time Stamp – A Novel Time-to-Digital Demodulation Method for Bioimpedance Implant Applications

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Time Stamp – A Novel Time-to-Digital Demodulation Method for Bioimpedance Implant Applications

Wu, Y; Jiang, D; Habibollahi, M; Almarri, N; Demosthenous, A; (2020) Time Stamp – A Novel Time-to-Digital Demodulation Method for Bioimpedance Implant Applications. IEEE Transactions on Biomedical Circuits and Systems , 14 (5) pp. 997-1007. 10.1109/TBCAS.2020.3012057. Green open access

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Abstract

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 ( fclk = 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.

Type:	Article
Title:	Time Stamp – A Novel Time-to-Digital Demodulation Method for Bioimpedance Implant Applications
Open access status:	An open access version is available from UCL Discovery
DOI:	10.1109/TBCAS.2020.3012057
Publisher version:	https:/doi.org/10.1109/TBCAS.2020.3012057
Language:	English
Additional information:	This version is the author accepted manuscript. For information on re-use, please refer to the publisher’s terms and conditions.
Keywords:	Demodulation, Bioimpedance, Impedance, Current measurement, Gain, Implants, Biomedical measurement
UCL classification:	UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Engineering Science > Dept of Electronic and Electrical Eng
URI:	https://discovery.ucl.ac.uk/id/eprint/10112478