A Scalable 32–56 Gb/s 0.56–1.28 pJ/b V oltage-Mode VCSEL-Based Optical Transmitter in 28-nm CMOS

Abstract

An optical transmitter (TX) data path is demonstrated in 28-nm CMOS which drives an 850-nm vertical- cavity surface-emitting laser (VCSEL) up to 56 Gb/s non- return-to-zero (NRZ). A dc-coupled single-ended voltage-mode driver employs area- and energy-efficient equalization techniques including slew-rate-based pulse-shaping at <40 Gb/s, active shunt peaking, and a three-tap feed-forward equalizer (FFE) at ≥40 Gb/s, for an optimum TX optical eye. At a 56 Gb/s data rate, the energy efficiency of 1.28 pJ/b from a 1.15 V supply is measured which is >2× more energy- and area-efficient than optical TXs reported to date. The highly digital circuit architec- ture enables the supply scalability to 0.7 and 0.85 V to operate the TX at 32 and 40 Gb/s at 0.56 and 0.77 pJ/b, respectively, which is ≥4× more energy-efficient than the prior art.