A Linear Inductorless SiGe BiCMOS TIA With <2% THD for 64-GBaud Coherent Optical Receivers

This letter presents the design methodology and implementation of a 64-GBaud (128-Gb/s) linear differential transimpedance amplifier (TIA) for high-speed coherent optical links. By employing a two-stage topology of a common-base (CB) input stage and a shunt-feedback (SFB) amplification stage, the TIA core generates a high-frequency peaking itself, which efficiently extends TIA's bandwidth (BW) without compromising the noise performance. The TIA achieves a measured maximum transimpedance gain (ZT) of 72 dBSt with -3-dB BW > 67 GHz, gain dynamic range of 30 dB, input reference noise (IRN) current root density <25.8 pA/ Hz, and total harmonic distortion (THD) <2% for 600-mVpp output swing at 3.2-mApp input photodiode (PD) current. With the pseudorandom bit sequence (PRBS) length of 231-1, the TIA is further demonstrated to operate up to 64-GBaud PAM4 eye diagram. The TIA occupies a total area of 1.09 mm2 and dissipates 336.6 mW from a 3.3-V voltage supply.