A 20/40 Gb/s NRZ/PAM4 Dual-mode Transmitter with 3-Tap FFE in 65 nm CMOS

This paper introduces a dual-mode transmitter that supports NRZ/PAM4 at a rate of 20/40 Gb/s. The 4:1 serializer consisted by latch and MUX synthesizes low-speed 5 Gb/s NRZ signals into 20 Gb/s NRZ signals. Three-tap feed-forward equalizer (FFE), which is realized by the source level capacitance degeneration delay unit calibrated by load resistance and source capacitance, and multiplier-adder, pre-emphasizes the high-speed NRZ/PAM4 signals to enhance the high-frequency components. The entire sending end circuit consumes 343.2 mW at 40 Gb/s with PAM4 mode and 296.2 mW at 20 Gb/s with NRZ mode at the supply voltage of 1.2 V.