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A state-of-the-art low-noise transimpedance amplifier (TIA) for 2.5 Gb/s family is presented using IBM 0.13-µm CMOS technology. This TIA woul d be a pa rt of a homod yne detector in a quantum ke y distribution (QKD) sy stem. In this work a thorough design methodology based on a novel analytical noise optimization is presented. Also a unique method for eliminating the DC current o f the input photodiodes (PDs) is proposed. The post-layout simulation results show bandwidth of 52 kHz to 1.9 GHz, average input referred noise of 1.93 pA/Hz, and transimpedance gain of 80 db while dissipating 12 mW from a 1.5 V power supply, including the output buffer.

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This paper reports on design and measurement results of a state of the art low-noise and high-gain transimpedance amplifier (TIA) implemented in 0.18 μm TSMC CMOS technology. Thorough design methodology for high gain and low power TIA design for 2.5 Gb/s optical communication circuits family is presented. A noiseless capacitive feedback is proposed and implemented as a noise efficient feedback network for TIA circuits. Besides, analytical noise calculations in this family of TIA circuits are presented and optimum noise criteria are derived. The saturation and instability problem of TIA circuits resulted from DC dark current of the input photodiodes (PDs) is addressed and a circuit level solution is presented. The measurement results of 0.18 μm chip shows bandwidth of 52 kHz to 1.62 GHz, and transimpedance gain of 75.5 dB while dissipating 26.3 mW from a 2.2 V power supply, including the output buffer. Taking advantage of proposed capacitive feedback network and optimum noise criteria, noise measurement results show average input referred current noise of 3.18 pA/Hz for this TIA in the bandwidth of operation. Index Terms-Current-input circuits, low-noise circuits, optical communications, transimpedance amplifiers I. INTRODUCTIONECENTLY, transimpedance amplifiers are being used in a very wide range of applications such as optical communications (families of 2.5, 10, 25,... Gb/s), mechanical sensors, biosensors, and other specific bio-applications like DNA sequencing, and impedance spectroscopy [1][2][3][4]. This broad range of applications results in different sets of constrains for a circuit designer when designing a TIA. While in high speed families of optical communication circuits the main goal is pushing the bandwidth of TIA higher in GHz range [4], bio-application TIAs usually stay in much lower frequency ranges but at the same time demand better noise performances and lower power consumption for chronic/long-term implantable versions [1][2][3]. So, the first question to be addressed in a TIA design is which application