A Capacitive Feedback 80 dBΩ 1.1 GHz CMOS Transimpedance Amplifier with Improved Biasing

The work presents the design of an area-efficient low-noise high-performance CMOS transimpedance amplifier for optical time-domain reflectometers. The proposed solution is based on a low-noise capacitive feedback structure and shows a gain of 83/80 dBΩ with the bandwidth reaching 1.1 GHz and average input-referred noise current density below $1.8 \mathrm{pA}/\sqrt{\mathrm{Hz}}$ in the presence of a 0.7 pF total input capacitance. The noise-efficient feedback structure allows addressing noise problem of conventional feed-forward or resistive feedback devices with the total power consumption around 21 mW while running at 1.8 V power supply. A more accurate design methodology is proposed based on explicit modeling of the biasing circuits and decoupling capacitor and modifications to the reference design are suggested including circuits for PMOS-based biasing and DC current elimination.