112-Gb/s PAM-4 Transmitter With Differential Encoding and XOR Driver in 28-nm CMOS

This article presents a 112-Gb/s pulse amplitude modulation 4-level (PAM-4) transmitter (TX) with differential encoding and XOR (exclusive OR) driver in 28-nm CMOS technology. Compared to the TXs using a 4:1 multiplexer (MUX) based on four-way interleaved 1-UI pulse generators, this design utilizes an XOR driver for serialization, which reduces the loading of the four-phase 14-GHz clock and eliminates the use of 1-UI pulse generator circuit to save power consumption. The main innovations of this work include the differential encoder RZ (return-to-zero) retimer, and XOR tailless driver. The simulation results indicate that the energy efficiency for the PAM-4 TX is 1.13pJ/b at 112 Gb/s with a 1-Vppd output amplitude.