A Wireless Injectable Device for Multimodal Animal Physiological Monitoring

This paper presents a wireless multimodal physiological monitoring application-specific integrated circuit (ASIC) fabricated in the 180 nm process and assembled in an injectable device to measure photoplethysmography (PPG), electrocardiography (ECG), and subcutaneous body temperature of animals. The device miniaturization is achieved by a shared receiver (Rx) coil and inductive link for both wireless power transfer (WPT) and data communication. An optimized folded Lshape Rx coil enhances the quality $(Q)$ factor, coupling with the transmitter (Tx) coil without increasing the device size. To facilitate WPT, the ASIC alternates between recording and lowpower sleep modes, achieving $2.54 \mu \mathrm{~W}$ ultra-low power consumption on average. The ECG analog frontend (AFE) amplifies the ECG signal with an adjustable gain of 45-80 dB and an input-referred noise (IRN) of $0.99 \mu \mathrm{~V}_{\mathrm{Rms}}$, while the PPG AFE achieves an IRN of 30.8 pArms. The temperature AFE provides a $27-47^{\circ} \mathrm{C}$ sensing range with $0.02{ }^{\circ} \mathrm{C}$ inaccuracy. The AFE outputs are sequentially quantized by a 10-bit analog-to-digital converter (ADC) with 54.7 dB signal-to-noise-and-distortion ratio (SNDR). For reliable data transmission, the ASIC employs a memoryassisted backscatter scheme, storing data in an 8 Mb memory chip and transmitting it when the inductive link is stable. The ASIC functionality has been validated in vivo on anesthetized rats.