A low-power dual-mode 20-Gb/s NRZ and 28-Gb/s PAM-4 voltage-mode transmitter

A dual-mode NRZ/PAM-4 differential low-swing voltage-mode transmitter employs a quarter-rate output multiplexing architecture for low-power operation. In NRZ mode, 2-tap feedforward equalization is realized with analog replica-bias tap control that is configurable in high-performance controlled-impedance or energy-efficient impedance-modulated settings. This analog control also allows for efficient generation of the middle levels in PAM-4 operation. Fabricated in GP 65nm CMOS, the transmitter supports an output swing range of 100–400mV P pd with up to 12dB of equalization in NRZ mode and achieves energy efficiencies of 1.48 and 0.91pJ/b at 20-Gb/s NRZ and 28-Gb/s PAM-4 data rates. Operation in the NRZ energy-efficient impedance-modulation setting allows for power savings of up to 32% relative to the controlled-impedance setting.