A 112-Gb/s PAM-4 Transmitter With a 2-Tap Fractional-Spaced FFE in 65-nm CMOS

This letter presents a 112-Gb/s four-level pulse amplitude modulation (PAM-4) transmitter with a 2-tap fractional-spaced feed-forward equalizer (FFE) implemented in a 65-nm CMOS process. The tap delay is adjusted by a coarse-fine capacitor array-based delay cell located in the clock path. Dynamic latches, pseudo-AND2s, and bandwidth-enhanced 4:1 MUXs are employed to guarantee an adequate timing margin and a sufficient bandwidth for the 112-Gb/s design. The measurement results show that the fractional-spaced FFE can significantly optimize the eye opening. The fabricated PAM-4 transmitter achieves a maximum data rate of 112 Gb/s with an energy efficiency of 2.17 pJ/bit.