In this article, we present the design and analysis of a 785-nW multimodal sensor interface IC for ozone pollutant sensing and correlated cardiovascular disease monitoring based on electrocardiography (ECG) and photoplethysmography (PPG). The proposed hybrid dc offset current cancellation (DCOC) along with a 4- MΩ gain-regulated cascode transimpedance amplifier (RGC-TIA) enable PPG readout power reduction by 37×, compared with the state-of-the-art PPG sensor interfaces. The ozone sensing channel proposes an adaptive architecture to enable low V _DD operation, achieving a 300× power reduction, compared with the state-of-the-art gas sensing readouts. The ozone sensing channel's performance was also verified using custom resistive metal-oxide sensors for concentrations from 50 to 900 ppb. The sensor interface IC is fabricated in a 65-nm CMOS, integrating a 165-nW voltage-mode ECG channel, a 532-nW current-mode PPG channel, 76-nW resistive-mode ozone channel, and 12.6-nW peripheral circuits, all at 0.6 V. The total system power consumption including the LED and a custom digital readout IC is 10.98- 15.51 μW, which is 41×- 57× less than prior ozone/CVD joint monitoring sensor interface systems.

This paper presents a 1.05 MHz, on-chip RC relaxation oscillator (ROSC) with a temperature coefficient (TC) of 2.5 ppm/°C and an absolute variation of 100 ppm over the body-compatible range of 0-40°C. The TC increases to 4.3 ppm/°C over the range from -15 °C to 55 °C. The high temperature stability is achieved using a PTAT current reference and a TC-tunable resistor bank for first-order frequency error compensation along with a digital frequency compensation (DFC) block using a single-bit temperature sensor for second-order compensation. A measured RMS period jitter of 160 ps is achieved with a high-speed comparator. The active power consumption of the ROSC is 69 μW with a 1-V supply, and the leakage power consumption is 110 nW, while power gated. The ROSC achieves a fast startup time of 8 μs by employing a voltage buffer to quickly stabilize the voltage reference.

This paper presents a tri-modal self-adaptive photoplethysmography (PPG) sensor interface IC for concurrently monitoring heart rate, SpO ₂ , and pulse transit time, which is a critical intermediate parameter to derive blood pressure. By implementing a highly-reconfigurable analog front-end (AFE) architecture, flexible signal chain timing control, and flexible dual-LED drivers, this sensor interface provides wide operating space to support various PPG-sensing use cases. A heart-beat-locked-loop (HBLL) scheme is further extended to achieve time-multiplexed dual-input pulse transit time extraction based on two PPG sensors placed at fingertip and chest. A self-adaptive calibration scheme is proposed to automatically match the chip's operating point with the current use case, guaranteeing a sufficient signal-to-noise ratio for the user while consuming minimum system power. This paper proposes a DC offset cancellation (DCOC) approach comprised by a logarithmic transimpedance amplifier and an 8-bit SAR ADC, achieving a measured 38 nA residue error and 8.84 μ A maximum input current. Fabricated in a 65nm CMOS process, the proposed tri-modal PPG sensor interface consumes 2.3–5.7 μ W AFE power and 1.52 mm ² die area with 102dB (SpO ₂ mode), 110–116 dB (HR & PTT mode) dynamic range. A SpO ₂ test case and a HR & PTT test case are both demonstrated in the paper, achieving 18.9 μ W and 43.7 μ W system power, respectively.