A 52-Gb/s Sub-1-pJ/bit PAM4 Receiver in 40-nm CMOS for Low-Power Interconnects

Abstract

This article presents a quarter-rate source-synchronous PAM-4 receiver for energy-efficient chip-to-module communication. A novel single-stage multiple peaking continuous-time linear equalizer (MP-CTLE) using feedback enabled multiple peaking scheme for both high-frequency equalization (HF-EQ) and low-frequency equalization (LF-EQ) is proposed to improve the BER performance and overall energy efficiency. The LF-EQ of the MP-CTLE eliminates the need for many DFE taps in SR/VSR applications to save power and area. A 1-tap feedforward equalizer (FFE) is used to further compensate for the high-frequency loss. We also use a ring oscillator based wide bandwidth phase-locked loop (WBW-PLL) as the multiphase clock generator (MPCG) in the clock and data recovery loop to save power with acceptable phase accuracy. Fabricated in 40-nm CMOS technology, the prototype receiver chip achieves error-free operation up to 52 Gb/s PAM-4 with superior bit efficiency of 0.126pJ/bit/s/dB while compensating 7.3-dB channel loss at 13GHz. With the proposed single-stage MP-CTLE, the receiver extends the error-free operation from PRBS-7 to PRBS-9. The BER bathtub curve at $10^{-6}$ is improved from 0.018 UI to around 0.1 UI.