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

Low-Phase-Noise CMOS Relaxation Oscillators for On-Chip Timing of IoT Sensing Platforms

The design of low-phase-noise fully integrated frequency references is often a critical aspect in the development of low-cost integrated circuits for communication interfaces, sensing platforms, and biomedical applications. This work first discusses relaxation oscillator topologies and design approaches aimed at minimizing the phase noise; then, a single-comparator low-phase-noise RC relaxation oscillator is proposed, featuring a novel comparator self-threshold-adjustment technique. The oscillator was designed for a 10 MHz oscillation frequency. Electrical simulations performed on a 0.18 μm CMOS design confirmed that the proposed technique effectively rejects the flicker component of the comparator noise, allowing for a 152 dBc/Hz figure of merit at a 1 kHz offset frequency. The standard deviation of the jitter accumulated across 10k oscillation cycles is lower than 4 ns. The simulated current consumption of the circuit is equal to 50.8 μA with a 1.8 V supply voltage. The temperature sensitivity of the oscillation frequency is also notably low, as its worst-case value across process corners is equal to −20.8 ppm/°C from −55 °C to 125 °C.

Machine Learning in Health Promotion and Behavioral Change: Scoping Review

BACKGROUND

Despite health behavioral change interventions targeting modifiable lifestyle factors underlying chronic diseases, dropouts and nonadherence of individuals have remained high. The rapid development of machine learning (ML) in recent years, alongside its ability to provide readily available personalized experience for users, holds much potential for success in health promotion and behavioral change interventions.

OBJECTIVE

The aim of this paper is to provide an overview of the existing research on ML applications and harness their potential in health promotion and behavioral change interventions.

METHODS

A scoping review was conducted based on the 5-stage framework by Arksey and O'Malley and the PRISMA-ScR (Preferred Reporting Items for Systematic Reviews and Meta-Analyses for Scoping Reviews) guidelines. A total of 9 databases (the Cochrane Library, CINAHL, Embase, Ovid, ProQuest, PsycInfo, PubMed, Scopus, and Web of Science) were searched from inception to February 2021, without limits on the dates and types of publications. Studies were included in the review if they had incorporated ML in any health promotion or behavioral change interventions, had studied at least one group of participants, and had been published in English. Publication-related information (author, year, aim, and findings), area of health promotion, user data analyzed, type of ML used, challenges encountered, and future research were extracted from each study.

RESULTS

A total of 29 articles were included in this review. Three themes were generated, which are as follows: (1) enablers, which is the adoption of information technology for optimizing systemic operation; (2) challenges, which comprises the various hurdles and limitations presented in the articles; and (3) future directions, which explores prospective strategies in health promotion through ML.

CONCLUSIONS

The challenges pertained to not only the time- and resource-consuming nature of ML-based applications, but also the burden on users for data input and the degree of personalization. Future works may consider designs that correspondingly mitigate these challenges in areas that receive limited attention, such as smoking and mental health.

Design of a Capacitance-to-Digital Converter Based on Iterative Delay-Chain Discharge in 180 nm CMOS Technology

The design of advanced miniaturized ultra-low power interfaces for sensors is extremely important for energy-constrained monitoring applications, such as wearable, ingestible and implantable devices used in the health and medical field. Capacitive sensors, together with their correspondent digital-output readout interfaces, make no exception. Here, we analyse and design a capacitance-to-digital converter, based on the recently introduced iterative delay-chain discharge architecture, showing the circuit inner operating principles and the correspondent design trade-offs. A complete design case, implemented in a commercial 180 nm CMOS process, operating at 0.9 V supply for a 0-250 pF input capacitance range, is presented. The circuit, tested by means of detailed electrical simulations, shows ultra-low energy consumption (≤1.884 nJ/conversion), excellent linearity (linearity error 15.26 ppm), good robustness against process and temperature corners (conversion gain sensitivity to process corners variation of 114.0 ppm and maximum temperature sensitivity of 81.9 ppm/°C in the -40 °C, +125 °C interval) and medium-low resolution of 10.3 effective number of bits, while using only 0.0192 mm2 of silicon area and employing 2.93 ms for a single conversion.

A readout circuit realizing electrochemical impedance spectroscopy for FET-based biosensors

Electrochemical impedance spectroscopy (EIS) is a useful approach for modeling the equivalent circuit of biosensors such as field-effect transistor (FET)-based biosensors. During the process of sensor development, laboratory potentiostats are mainly used to realize the EIS. However, those devices are normally not applicable for real use-cases outside the laboratory, so miniaturized and optimized instrumentations are needed. Various integrated circuits (IC) are available that provide EIS, but these make developed systems highly dependent on semiconductor manufacturers, including component availability. In addition, these generally do not meet the instrumentation requirements for FET-based biosensors, thus external circuitry is necessary as well. In this work, an instrumentation is presented that performs EIS between 10 Hz and 100 kHz for FET-based biosensors. The instrumentation includes the generation of the excitation signal, the configuration of the semiconductor and the readout circuit. The readout circuit consists of a transimpedance amplifier with automatic gain adjustment, filter stages, a magnitude and a phase detection circuit. Since magnitude and phase are converted to a DC signal, digitization of the results is trivial without further signal processing steps, minimizing the computational load on the microcontroller. The transmission behavior of the magnitude and phase measurement circuits shows a high linearity for sinusoidal signals. Furthermore, the overall system was tested with resistors, whereby the magnitude measurement error (1.7%) and the phase shift error (1.6°) were determined within the working range of the instrumentation. The functionality of the instrumentation is demonstrated using pH-sensitive field-effect transistors (ISFET) in various solutions.Clinical relevance- Based on the electrochemical impedance spectroscopy of FET-based biosensors such as ImmunoFETs, new point-of-care testing (POCT) devices can be developed that e.g. quantitatively detect the concentration of biomarkers with very low detection limits in body fluids. The instrumentation presented in this work can be part of new generation of diagnostic tools featuring innovative sensor technologies.

A Low-Power CMOS Bandgap Voltage Reference for Supply Voltages Down to 0.5 V

A voltage reference is strictly required for sensor interfaces that need to perform nonratiometric data acquisition. In this work, a voltage reference capable of working with supply voltages down to 0.5 V is presented. The voltage reference was based on a classic CMOS bandgap core, properly modified to be compatible with low-threshold or zero-threshold MOSFETs. The advantages of the proposed circuit are illustrated with theoretical analysis and supported by numerical simulations. The core was combined with a recently proposed switched capacitor, inverter-like integrator implementing offset cancellation and low-frequency noise reduction techniques. Experimental results performed on a prototype designed and fabricated using a commercial 0.18 μm CMOS process are presented. The prototype produces a reference voltage of 220 mV with a temperature sensitivity of 45 ppm/°C across a 10–50 °C temperature range. The proposed voltage reference can be used to source currents up to 100 μA with a quiescent current consumption of only 630 nA.

Low-Power Wearable Healthcare Sensors

Medical science has taken great steps to enable us to live longer and healthier lives [...]

Recent progress, challenges, and prospects of fully integrated mobile and wearable point-of-care testing systems for self-testing

The rapid growth of research in the areas of chemical and biochemical sensors, lab-on-a-chip, mobile technology, and wearable electronics offers an unprecedented opportunity in the development of mobile and wearable point-of-care testing (POCT) systems for self-testing. Successful implementation of such POCT technologies leads to minimal user intervention during operation to reduce user errors; user-friendly, easy-to-use and simple detection platforms; high diagnostic sensitivity and specificity; immediate clinical assessment; and low manufacturing and consumables costs. In this review, we discuss recent developments in the field of highly integrated mobile and wearable POCT systems. In particular, aspects of sample handling platforms, recognition elements and sensing methods, and new materials for signal transducers and powering devices for integration into mobile or wearable POCT systems will be highlighted. We also summarize current challenges and future prospects for providing personal healthcare with sample-in result-out mobile and wearable POCT.

High Sensitivity, Humidity-Independent, Flexible NO2 and NH3 Gas Sensors Based on SnS2 Hybrid Functional Graphene Ink

Here, a high sensitivity gas sensing ink based on sulfonated rGO (S-rGO) decorated with SnS₂ is synthesized for room temperature NO₂ and NH₃ detection. This sensing ink demonstrated an excellent sensitivity to ppb-level NO₂ (17% response to 125 ppb) and sub-ppm-level NH₃ (11% response to 1 ppm). The unique absorption properties of SnS₂ improve the sensitivity of S-rGO 4.2 and 55 times to NO₂ and NH₃, respectively. Besides, the superhydrophobicity of the SnS₂ endows the sensor with exceptional immunity to high relative humidity (RH). Furthermore, the sensors exhibit negligible degradation to NO₂ and less than 15% degradation to NH₃ in a wide range of RH from 30 (ambient humidity) to 90%. More importantly, the obtained full-written ink can be applied to common substrates, such as glass, clothes, and paper, and maintain excellent performance after being bent and twisted by 180°.