UC Berkeley

Light-to-digital converters are critical in bio-signal acquisition systems such as photoplethysmography (PPG) and fluorescence sensors. These applications demand converters with low input-referred noise (IRN) and high dynamic range (DR) to detect low-level signals from sensing targets in the presence of large varying background levels. Typically, noise performance is limited by the operational transconductance amplifier (OTA) in the capacitive transimpedance amplifier (CTIA) and kT/C noise sampled on the feedback capacitor. kT/C noise is commonly canceled through correlated double sampling, which suffers from noise folding of the high frequency OTA noise. This work presents a four-channel light-to-digital converter IC that utilizes multisample line fitting to suppress kT/C noise and noise folding. A power-efficient gain-boosted folded-cascode OTA topology is employed within the CTIA to further reduce the dominant noise during integration. Compared to recent light-to-digital converter designs, the fabricated IC achieves the lowest IRN of $12.9 \text{fA} / \text{rtHz}$, the best power efficiency of $0.646 \text{fA}^{2} \cdot ~\mathrm{W} / \text{Hz}$, and a high DR of 119.4 dB.