A High-Output-swing 64-Gb/s PAM-4 Transmitter with a 4-Tap Hybrid FFE in 28-Nm CMOS.

This article presents a high -output -swing 64-Gb/s four -level pulse amplitude modulation (PAM -4) transmitter, in which a 4 -tap hybrid feed -forward equalizer (FFE) employing both fractionally -spaced preemphasis (FS -PE) and baud -spaced de -emphasis (BS -DE) is proposed. The PE technique enlarges the output swing by directly stacking pre -distortion pulses, and naturally consumes less power as it boosts only the desired symbols. The FS -based pre/post1 taps equalize the high -frequency loss, provide a wide compensation range beyond the Nyquist frequency, and realize a flexible equalization capability, while the BS -DE -based post2 tap compensates for the low -frequency channel loss. Fabricated in a 28-nm CMOS process, the 64-Gb/s transmitter obtains a differential output swing of 1.4 Vppd with an energy efficiency of 1.53 pJ/bit.