The world has been in combat with COVID-19 since December 2019. The United States has been paralyzed, with the highest number of cases and more deaths than any other country. However, the disease has devastated almost every nation across the globe, from the Far East to Europe, Latin America, Russia, and India.

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Emerging Blood Gas Monitors: How They Can Help With COVID-19

Remote home monitoring via wearables is rapidly gaining popularity, thanks to ever more complex vital signs recording and data analytics that are embedded into single devices. True system-on-chips (SoCs) push the envelope of power and form factor, while wearables are becoming more common-place, novel health sensing paradigms appear. Non-contact sensing technologies enable vital signs sensing without requiring any physical contact with the human body. This article reviews existing multiple-modality bio-signal recording and processing SoCs, circuit techniques for individual bio-signal readout channels including electrocardiography (ECG), Electroencephalography (EEG), Bio-impedance (BioZ), photoplethysmography (PPG), and non-contact sensing with high user comfort. The state-of-the-art wearable sensor interfaces and systems together with future development trends are provided.

Wearable Multiple Modality Bio-Signal Recording and Processing on Chip: A Review

Electrochemical sensing has been widely applied to a variety of applications involving disease diagnosis due to its ability to measure targets directly, fast response, and high accuracy compared to other detection methods The accelerated uptake of point-of-care (POC) testing underscores the need for portable devices integrated with electrochemical sensing functions Noninvasive electrochemical sensing has also been studied with regard to the analysis of bodily fluids and represents a promising method for long-term tracking of patient health conditions A comprehensive understanding of electrochemical electrode and readout circuitry has led to increasing research on the use of electrochemical sensors for pharmaceuticals, biotechnology, and disease diagnosis applications This article reviews the state-of-the-art electrochemical readout interfaces using CMOS technology for biomarker detection

A Review of CMOS Electrochemical Readout Interface Designs for Biomedical Assays

This paper reports on a low-power readout IC (ROIC) for high-fidelity recording of the photoplethysmogram (PPG) signal. The system comprises a highly reconfigurable, continuous-time, second-order, incremental delta-sigma modulator (I–ΔΣM) as a light-to-digital converter (LDC), a 2-channel 10b light-emitting diode (LED) driver, and an integrated digital signal processing (DSP) unit. The LDC operation in intermittent conversion phases coupled with digital assistance by the DSP unit allow signal-aware, on-the-fly cancellation of the dc and ambient light-induced components of the photodiode current for more efficient use of the full-scale input range for recording of the small-amplitude, ac, PPG signal. Fabricated in TSMC 0.18 μm 1P/6M CMOS, the PPG ROIC exhibits a high dynamic range of 108.2 dB and dissipates on average 15.7 μW from 1.5 V in the LDC and 264 μW from 2.5 V in one LED (and its driver), while operating at a pulse repetition frequency of 250 Hz and 3.2% duty cycling. The overall functionality of the ROIC is also demonstrated by high-fidelity recording of the PPG signal from a human subject fingertip in the presence of both natural light and indoor light sources of 60 Hz.

A 280 μW, 108 dB DR PPG-Readout IC With Reconfigurable, 2nd-Order, Incremental ΔΣM Front-End for Direct Light-to-Digital Conversion

Photoplethysmography (PPG) is a key non-invasive technique to extract vital signs like heart rate (HR), heart rate variability (HRV), and blood oxygen saturation (SpO 2 ). Integrated in smartwatches, health patches and finger clips, PPG sensors are widely used in fitness, glucose, blood pressure, and medical monitoring with good user comfort. Integrating PPG in medical chest patches is interesting for COVID-19 patients since it can yield, next to HR and respiration, also SpO 2 , which traditional ECG-based patches cannot provide. However, measuring PPG/SpO 2 on the chest is challenging due to large motion artifacts, small AC/DC perfusion index (PI $\lt 0.1$%), and ambient light. Therefore, it poses a more stringent requirement on dynamic range (DR $\gt 120$ dB) for the PPG readout circuit, while still requiring low power consumption for long battery life. On-chip pinned-photodiodes (PPDs) have been used as passive integrators, resulting in very low power consumption $(2.63 \mu \mathrm{W})$ for the PPG readout [1]. However, the DR and linearity can be limited by the PPDs’ parasitic capacitors. Direct light-todigital converter (LDC) topologies are proposed in [2 - 4], but their DR is still below 120dB. In [5], a digital-controlled TIA is exploited to control the transimpedance gain, which extends the DR to 130dB while consuming $72 \mu \mathrm{W}$ in the analog front-end (AFE).

A 28μW 134dB DR 2nd-Order Noise-Shaping Slope Light-to-Digital Converter for Chest PPG Monitoring

Recently, biosensors have become widely deployed in consumer wearable devices, e.g., smart watches and wrist bands, to track user health conditions during sport, sleep, and daily activity. However, unlike biosignal acquisition in well-controlled medical settings, signal acquisition in consumer devices inevitably suffers from degraded signal quality due to poor sensor interfaces, motion artifacts, and environmental interferences, such as ambient light and power-line coupling, which can be >60dB stronger than the wanted signals. These challenges result in demanding AFE specifications, even under tight constraints on sensor area, chip size, and battery capacity, which are all necessary for wearable devices. This paper presents a multimodal biosensing SoC that addresses these issues to enable reliable Photoplethysmography (PPG), Electrocardiography (ECG), and Bio-impedance (BIOZ) acquisition under highly variable conditions in wearable devices. It contains a 130dB-DR PPG readout, which is 11dB higher than the state of the art [1], to tolerate strong ambient light; an ECG AFE with a pseudo Right-Leg-Drive (RLD) tolerant of >130V PP common-mode interference (CMI) from power-line coupling, which is 3× higher than the technique presented in [2]; and a BIOZ AFE for body-fat measurement using 1cm2 electrodes rather than the typically >10cm2 electrodes in conventional body-fat meters. The area for the entire PPG/ECG/BIOZ AFE is ~3mm2, which is around 50% smaller than prior AFEs with similar features [3], [4].

Teng-Feng Zou

Papers

26.1 A 4.5mm 2 Multimodal Biosensing SoC for PPG, ECG, BIOZ and GSR Acquisition in Consumer Wearable Devices