A Multi-Channel 133-dB DR PPG/ECG SoC for Smart Wearable Devices

Real-time monitoring of multimodal vital signs including electrocardiography (ECG) and photoplethysmography (PPG) on wearable devices are attracting increasing interests. Motion artifacts, ambient light interference and sensor-skin contact variability affect signal quality significantly, demanding a multi-channel sensor interface chip with high dynamic range yet low power. A PPG/ECG interface chip is proposed for robust signal optimization. Time-division multiplexing, ambient double sampling and DC current compensation together enhance the dynamic range. Fabricated in a 0.18μm process, the chip features a 5.63-pArms direct digitized input-referred noise for PPG readout and 365-nVrms for ECG. A cross-scale dynamic range of 133dB is achieved, providing saturation-free usage for sport wearable devices such as smart watches and rings.