A Shunt-Feedback TIA with Common-Base Variable Gain Input Stage for 128-GBaud Coherent Communication

We present a fully differential linear transimpedance amplifier − (TIA) with a common-base (CB) variable gain circuit as the input stage of a shunt-feedback (SFB) TIA circuit. A quad channel TIA chip is fabricated in 55-nm SiGe BiCMOS technology, and shows measured transimpedance gain of 70 $\text{dB}\Omega,$ 42-dB gain dynamic range, and 80-GHz bandwidth. An intradyne coherent receiver (ICR) with this TIA shows measured result of greater than 75-GHz bandwidth of O/E response. To the authors' knowledge, this is the highest bandwidth among the reported differential TIAs with the variable gain function. An experimental transmission evaluation of 128-GBaud single polarization 16 quadrature amplitude modulation (SP-16QAM) is implemented and an error vector magnitude (EVM) of 13.2% is observed.