0.41-pJ/b/dB Asymmetric Simultaneous Bidirectional Transceivers With PAM-4 Forward and PAM-2 Back Channels for 5-m Automotive Camera Link

This paper presents asymmetric simultaneous bidirectional (SBD) transceivers for the next-generation automotive camera link. To realize the SBD operation with the PAM-4 signaling, the proposed wide linear range (WLR) hybrid excludes the voltage-dependent non-linear transconductance (gm) of active elements. A two-step hybrid strategy suppressing the PAM-4 forward channel (FC), including the FFE, is utilized for low power and design simplicity. A Σα hybrid removes only four primary DC levels, and 2^nd order gm-capacitor (gmC) low-pass filter (LPF) filters out residual/echoes from the hybrid/channel. An echo canceller (EC) technique is also employed to further reduce the reflections of the PAM-2 back channel (BC). The highly asymmetric SBD transceivers with 12-Gb/s PAM-4 FC and 125-Mb/s PAM-2 BC achieve BER<10^-12 over 5-m cable (15.9 dB loss). Prototype chips fabricated in 40-nm technology consume 78.4 mW, exhibiting an FoM of 0.41 pJ/b/dB.