A Low Noise Transimpedance Amplifier for 2.5 Gb/s Optical Communications

The paper presents a low-noise transimpedance amplifier (TIA) for 2.5Gb/s optical communications using 0.35 mu m BiCMOS technology. For the gain boosting, Cherry-Hooper amplifier is introduced for the second stage amplification. Also a unique method for eliminating the DC current of the input photodiodes is proposed. In order to reduce the input equivalent noise current, a detailed mathematical analysis of the proposed TIA on noise optimization is given. Using this approach, the TIA achieves a constant gain of 70dB Omega from 50kHz to 2.7kHz when connected to a 0.6pF load at the input. The equivalent input current noise is 2.4pA/root Hz up to 1.6GHz. The amplifier remains linear up to 2mA and can withstand photodiode input DC currents up to 1mA. The typical power consumption of the amplifier is 73mW including the output buffer. The die size is 30mil x 50mil.