A Low-Noise 56Gbps PAM-4 Linear Optical Receiver in 40nm CMOS

A 56Gb/s PAM-4 low-noise linear optical receiver is presented. To reduce the input referred noise (IRN) and improve the sensitivity, the optical receiver front-end comprises of a high-gain narrow-bandwidth transimpedance amplifier (TIA) followed by a two-stage equalizer. The gain tunable TIA and the variable gain amplifier (VGA) with automatic gain control (AGC) loop ensure the linearity across the whole input range. Designed and implemented in 40nm CMOS technology, the receiver accomplishes 1.7μArms IRN, 78dBΩ transimpedance gain and 23GHz bandwidth while consuming 108mW from 1.6V supply. The dynamic range of transimpedance is 40dB, enabling large input overload current of 2.5mA
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and total harmonica distortion (THD) is below 3% with 800mV
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swing at the output.