Inductor-less low-noise CMOS transimpedance amplifier for OTDR applications

Abstract

The paper reports on the design of a low-cost high-gain CMOS transimpedance amplifier for optical time-domain reflectometers. The circuit is implemented using 180 nm TSMC technology and employs a noise-efficient capacitive feedback structure to address the noise problem typical for conventional design strategies with resistive feedback. The simulation results show a gain of 72.5 dBΩ with 3-dB bandwidth of 1 GHz and average input-referred noise current density below 5 pA√Hz in the presence of a 0.7 pF total input capacitance. The circuit including the output buffer consumes <20 mW while running from 1.8 V power supply. Several circuit-level modifications to the reference topology are introduced to address the issues such as DC current elimination, voltage headroom problems and typical parasitic capacitances in commercial CMOS technology.