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

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....

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Bibliographic Details
Published in:IEEE transactions on biomedical circuits and systems 2020-10, Vol.14 (5), p.997-1007
Main Authors: Wu, Yu, Jiang, Dai, Habibollahi, Maryam, Almarri, Noora, Demosthenous, Andreas
Format: Article
Language:English
Subjects:
Bioimpedance
Biological properties
Biomedical measurement
Circuits
CMOS
comparator
Comparators
Current measurement
Demodulation
Electrical properties
Gain
Impedance
impedance demodulation
implantable devices
Implants
Phase detectors
Power consumption
time-to-digital conversion
Tissue analysis
Tissues
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Summary: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 ({{\boldsymbol{f}}_{{\boldsymbol{clk}}} = 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.
ISSN:1932-4545
1940-9990
DOI:10.1109/TBCAS.2020.3012057