A 79 dBΩ 1.2 GHz Low-Noise Single-Ended CMOS Transimpedance Amplifier for High-Performance OTDR Applications

Abstract

The paper discusses the design methodology for a low-cost high-gain CMOS transimpedance amplifier for optical time-domain reflectometers. The circuit is implemented using 0.18 µm CMOS technology and employs a noise-efficient capacitive feedback structure to address the noise problem of conventional design approaches such as feed-forward or resistive feedback architectures. The simulation results show a gain of 82/79 dBΩ with 3-dB bandwidth of 1.2 GHz and average input-referred noise current density below 1.8 pA/sqrt(Hz) in the presence of a 0.7 pF total input capacitance. The circuit including the output buffer consumes around 21 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.