A Batteryless Sensor ASIC for Implantable Bio-impedance Applications

TL;DR

This paper introduces a compact, batteryless implantable bio-impedance sensor ASIC that accurately measures tissue impedance wirelessly, facilitating medical diagnostics and monitoring with minimal size and power consumption.

Contribution

It presents a novel 150 nm CMOS ASIC design for implantable bio-impedance measurement, enabling accurate, wireless, and batteryless operation in a miniature form factor.

Findings

Achieves ~1 Ohm resolution in impedance extraction.

Operates accurately from 2 kHz to 2 MHz frequency range.

Successfully validated through ex vivo animal tissue measurements.

Abstract

The measurement of the biological tissue's electrical impedance is an active research field that has attracted a lot of attention during the last decades. Bio-impedances are closely related to a large variety of physiological conditions; therefore, they are useful for diagnosis and monitoring in many medical applications. Measuring living tissues, however, is a challenging task that poses countless technical and practical problems, in particular if the tissues need to be measured under the skin. This paper presents a bio-impedance sensor ASIC targeting a battery-free, miniature size, implantable device, which performs accurate 4-point complex impedance extraction in the frequency range from 2 kHz to 2 MHz. The ASIC is fabricated in 150 nm CMOS, has a size of 1.22 mm x 1.22 mm and consumes 165 uA from a 1.8 V power supply. The ASIC is embedded in a prototype which communicates with, and is powered by an external reader device through inductive coupling. The prototype is validated by measuring the impedances of different combinations of discrete components, measuring the electrochemical impedance of physiological solution, and performing ex vivo measurements on animal organs. The proposed ASIC is able to extract complex impedances with around 1 Ohm resolution; therefore enabling accurate wireless tissue measurements.