Fully integrated CMOS avalanche photodiode and distributed-gain TIA for CW-fNIRS

This paper introduces a CMOS silicon avalanche photodiode (SiAPD) integrated on-chip with an optical trans-impedance amplifier (TIA) to be used in a fNIRS photo-receiver front-end. Proposed SiAPD has the avalanche gain of 200 with the depletion layer thickness of greater than 40μm, its breakdown voltage is 6V and its photon absorption efficiency is 95% and 40% at 700nm and 900nm respectively. The proposed TIA also has a low power consumption (4mW), high transimpedance gain (up to 250MV/A), tunable BW (100KHz-1MHz) and very low input and output noise (280fA/√Hz and 1.5mV/√Hz) all the essential requirements for fNIRS photoreceiver front-end. This circuit is developed using 0.35 CMOS technology and the measurement results verifying the efficiency and preference of this design comparing to the similar available circuits.