A $4\times45$ Gb/s Two-Tap FFE VCSEL Driver in 14-nm FinFET CMOS Suitable for Burst Mode Operation

This paper presents a high-swing vertical-cavity surface-emitting laser (VCSEL) driver with two-tap feed-forward equalizer (FFE) in 14-nm FinFET CMOS technology. The design features a standby mode with power-ON time below 10 ns and 86% of power saving. Based on system-level simulations, the impact of the driver swing, tap delay, and weight on the optical eye-opening is studied and it is shown that the FFE combined with high-swing driving can improve the output eye at rates beyond two times the bandwidth of the VCSEL. By applying an extra supply, the output stage is optimized to provide high swing (0.65 V) without suffering from the slow response of a transistor in the triode region. In addition, the bias and modulation currents can be adjusted to accommodate different VCSELs. The designed circuit is tested with two VCSEL types. It is bonded to common-cathode 20 and 18 GHz VCSELs, and in both the cases, data transmission at 45 Gb/s with bit error rate lower than 10−12 is measured. The total power dissipation is below 100 mW, providing a power efficiency of better than 2.11 pJ/bit. To the best of our knowledge, this design is the fastest VCSEL driver in any CMOS technology, which is also capable of burst mode operation.