100Gb/s PAM-4 VCSEL Driver and TIA for Short-Reach 400G-1.6T Optical Interconnects

This paper presents a chipset of multi-channel vertical-cavity-surface-emitting laser (VCSEL) driver and trans-impedance amplifier (TIA) in a 180-nm SiGe BiCMOS. Targeting 400G-1.6T short-reach applications, the high-speed linear gain is developed for the four four-level pulse amplitude modulation (PAM-4). The VCSEL driver employs a second-order continuous-time linear equalizer to compensate for non-linear input channel loss, while exploiting an RC-degenerated output stage with inductive shunt peaking to extend the bandwidth. The TIA adopts the resistive feedback topology along with a series-peaking inductor to improve its input bandwidth. Experimental results show the VCSEL driver operates up to 100 Gb/s with 280-mVpp PAM-4 modulated swing. The TIA achieves $61.5-\text{dB}\Omega$ trans-impedance gain, 36-GHz BW, and $16-\text{pA}/\surd \text{Hz}$ averaged input-referred noise.