Design of transimpedance amplifiers for broadband time-domain optical reflectometer systems

Abstract

The tremendous growth of Internet traffic in recent years had led to the rapid development of broadband optical communication systems. This rapid growth also increases a demand for the equipment for network deployment, monitoring and repair. One of the typically used instruments is based on a technique known as Optical Time-Domain Reflectometry - OTDR. These instruments are used for characterization and fault detection in optical fibers is based on the analysis of the reflections in time domain. The research object of the doctoral dissertation is the design and analysis of an programmable-gain CMOS TIA suitable for modern OTDR applications. In order to compare quantitatively different TIA architectures as well as designs produced using different technologies, the work suggests a quantitative measure - Figure-of-Merit (FOM). After evaluating advantages of different TIA types, the dissertation suggests a novel programmable-gain capacitive feedback TIA architecture with PMOS transistor-based biasing circuit for source follower which allows to implement a low-noise broadband TIA. Based on the suggested architecture and using 0.18 μm CMOS and 0.25 μm BiCMOS technologies, TIAs were designed with 1.0 GHz and 0.9 GHz bandwidths accordingly, 10 kΩ, 25 kΩ, 100 kΩ, 200 kΩ and 500 kΩ discretely adjustable gains, 1.8 and 1.6 pA/ √ Hz noise current spectral densities, 21 mW and 29 mW power consumption at correspondingly 1.8 V and 2.5 V supply voltages and their major characteristics were investigated. The dissertation consists of an introduction, three chapters, general conclusions, a list of references, the author’s publications on the topic of the dissertation and two appendices. The first chapter presents modern TIA architectures, their main parameters, proposed FOM measure and the OTDR requirements for frontend TIAs. The second chapter presents an analysis of the proposed TIA architecture and mathematical models for the transimpedance gain and input-referred noise current spectral density. The third chapter discusses the designed topologies for the proposed TIA architectures and compares the results of the computer simulation with those from the analytical models. The research results of this dissertation are summerized in general conclusions and a comprehensive bibliography with a list of the author’s seven publications on the topic of the dissertation are provided. The results of the dissertation were reported in 7 scientific publications: 3 of them are published in scientific journals referenced in Clarivate Analytics Web of Science database with 2 of them having citation index, 2publications in proceedings of international conferences included in Clarivate Analytics Proceedings database and 2 publications in conference proceedings included in other international databases. The results of the dissertation research were presented in 5 scientific conferences in Lithuania and abroad.