A DAC-Based 28Gb/s PAM4 Transmitter for Serial Link System

This paper presents a DAC-Based transmitter for serial link system. To balance speed and accuracy, the 7b DAC i s divided into 4 binary and 3 thermometer. To improve output impedance matching and reduce return loss, the CML driver is use d in the DAC unit cell. In addition, the quarter-rate 4:1MUX is used in the last stage of multiplexer, which is based on a 1UI pulse generator, reduces the design complexity of the clock circuit. T he DAC-Based TX implements serial 28Gb/s PAM4 output on 65 nm CMOS technology with differential output of 617 mVpp. At t he Nyquist frequency of 6.89GHz, SNDR=38.15dB, SNR=42.01d B, SFDR=40.44dBc, THD=-40.44dB. It consumes 152mW at 1.2 V supply voltage.