An 80-Gb/s PAM-4 Simultaneous Bidirectional Transceiver With Hybrid Adaptation Scheme

This brief presents a simultaneous bidirectional (SBD) transceiver with four-level pulse amplitude modulation (PAM-4), employing a novel hybrid adaptation scheme. The possibility of extending bandwidth is explored by applying PAM-4 signaling to SBD. Furthermore, a mismatch compensation method for a hybrid circuit is proposed, which is essential for removing the outbound signal in SBD. The hybrid adaptation is easily implemented by applying the locked condition of the Mueller Müller phase detector (MMPD) with the data level adaptation. By sharing one error sampler with MMPD and adaptation engine, the presented SBD transceiver is efficient in terms of clocking power consumption and bandwidth of a receiver front-end. A wide linear range hybrid and a data alignment technique guarantee the robust PAM-4 SBD operation. Fabricated in the 28-nm CMOS, the 80-Gb/s SBD transceiver achieves a bit error rate (BER) of less than $10^{-12}$ with an energy efficiency of 2.65 pJ/b.