56Gbaud Linear PAM4 Transimepedance Amplifier and VCSEL Driver in 55nm BiCMOS Technology

A linear 56Gbaud PAM4 transimpedance amplifier (TIA) and a VCSEL-based driver are presented in this paper. It can meet the requirements of emerging 400G Ethernet. The equalizer technique is both adopted in TIA and driver to extend bandwidth. The AGC in TIA can provide 33.4dB gain control range and it accommodates input currents from 35uApp up to 2 mApp. To improve its linearity, the driver adopts feedforward equalizer(FFE) to decrease its group delay peak-peak value. By using advanced SiGe BiCMOS technology, the operating bits rates of each channel in TIA and driver can be up to 112Gbps.