A 56-Gbps PAM4 amplitude-rectification-based receiver with threshold adaptation and 1-tap DFE

This paper presents a 56-Gbps four-level pulse amplitude modulation (PAM4) quarter-rate receiver based on amplitude rectification. Compared with the conventional three-comparator structure, the PAM4 signal is converted into a 2-digit gray-code rather than a 3-digit thermometer-code. The amplitude is detected to decode the least significant bit (LSB), which allows the proposed receiver to use significantly less power by reducing the number of comparators. An inverter-based common-mode voltage stabilization circuit (CVSC) is proposed to reduce the effect of common-mode level changes as the amplitude is determined. To minimize the feedback delay, the 2-digit gray-code is fed back to DFE's summer directly. By reducing the digit of the feedback signal, the power will be further reduced as the DFE tap increases. The device consumes 83.5 mW over a 55-nm process.