A Batteryless Sensor ASIC for Implantable Bio-Impedance Applications

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 × 1.22 mm and consumes 165 μA 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 Ω resolution; therefore enabling accurate wireless tissue measurements.

CMOS Interfaces for Internet-of-Wearables Electrochemical Sensors: Trends and Challenges

“…When the stimulus is applied as a voltage, imposed between the reference electrode and the working electrode, the current flowing through the working electrode is acquired. Current stimulation is not common in EIS systems but is frequently used in bio-impedance measurement devices [178][179][180], where it is not important to set a precise DC bias. The most popular approach for the development of compact EIS systems is using voltage stimulation combined with FRA operating principles.…”

“…Due to the need for sweeping the frequency across intervals several decades wide, classical RC or LC oscillators are not adequate for generating the stimulus. The preferred solution is synthesizing the sinusoid by means of a conventional R-2R [181] or resistor-string [179] DAC, starting from a set of samples.…”

“…In Ref. [179], a Gm-C filter that relies on external capacitors is employed, whereas an external filter/amplifier is used in [182]. An alternative solution, corresponding to multiplying the EIS interface response by a discretized sinusoidal reference, is proposed in [181].…”

Mixed-level simulation tool for design optimization of electrical impedance spectroscopy systems

“…Since the tool is intended to help design integrated circuit systems, the Cadence platform was chosen. We have developed a library of high-level and low-level mod-Brought to you by | Stockholm University Library Authenticated Download Date | 2/4/19 3:32 PM els of the mainly used blocks for impedance spectroscopy from the literature [4][5][6]. For high-level models we use Verilog-AMS, which is a derivative of the Verilog hardware description language that enables designers to create analog and mixed-signal modules containing high-level behavioral descriptions of the system blocks.…”

A Novel Passive Method for the Assessment of Skin-Electrode Contact Impedance in Intraoperative Neurophysiological Monitoring Systems

“…The common method for measuring the electrode-tissue impedance consists of injecting a known AC current 14 (usually a square wave) and measuring the differential voltage between the electrodes 6,15 ; this methodology is applied to measure bio-impedance in general. For example, Zamani et al 16 present a bio-impedance measurement system for cardiac tissues, and Rodriguez et al 17 describe a wireless sensor suitable for implantable devices. Multifrequency analysis can be found in the literature, applied for example to cardiac tissues 18 , in order to extend the analysis of the impedance to the range of frequencies of the measured signals.…”