A Differential Push-Pull Voltage Mode VCSEL Driver in 65-nm CMOS

Improving power-conversion efficiency (PCE) of VCSEL drivers is paramount to improve the overall energy efficiency of the entire optical link for high-performance computing and data centers. VCSEL diodes are normally driven single-ended with pseudo-differential current-mode drivers to maintain signal integrity. However, such conventional drivers consume significant power and are often unable to compensate for supply switching noise due to package parasitics at high data-rates. We propose a differential push-pull voltage-mode VCSEL driver to mitigate bondwire parasitics, reduce power consumption, and leverage CMOS process scaling to its maximum advantage. A proof-of-concept prototype in 65-nm CMOS process achieves the highest ever-reported PCE of 18.7 % for VCSEL drivers when normalized to VCSEL slope efficiency. It uses an asymmetric 3-tap rise and fall-based pre-emphasis to achieve a total energy/bit of 1.52 pJ/b at 16 Gb/s with an average optical power output of 1.34 dBm, OMA of 2.1 dBm, and extinction ratio of 5.92 dB.