A 44 Gbps PAM-4 Transmitter with Resistance Feedback 4:1 MUX in 65nm CMOS

This paper presents a power-efficient four-level pulse amplitude modulation (PAM-4) transmitter with 4-tap feed-forward equalizer (FFE) SST driver. A resistance feedback 4:1 MUX is proposed to overcome the bandwidth limit in the last MUX node. The bandwidth is improved more than twice and the jitter is reduced from 7.07ps to 381fs. An absolute delay-based clock distribution network is designed to ensure the timing of the 4:1 MUX. The PAM-4 transmitter is fabricated in 65nm CMOS process and occupies 1.53mm×1.35mm. It delivers a 1.2Vppd PAM-4 signal with RLM of 99% under 1.2V supply and achieves an energy efficiency of 2.27pJ/bit at 44Gbps.