Power supply noise-induced performance degradation in transmitter: An analysis of eye height and vertical eye closure at 106.25 Gbps data rate

This paper investigates the adverse effects of Switched Mode Power Supply (SMPS) noise, particularly its switching frequency, on the transmitter’s electrical output jitter and noise characteristics within a high-speed 106.25 Gbps PAM4 chip-to-module (C2M) SerDes channel in a high-density router. For the specified channel, IEEE 802.3ck stipulates two essential transmitter parameters: Eye Height (EH $\ge 10$ mV) and Vertical Eye Closure (VEC $\le 12$ dB). Ensuring compliance with these parameters is crucial for the product to meet the standard.However, when switched at a nominal 416 KHz frequency, the power supply induced significant spur at the fundamental frequency and its harmonics leading to a high transmitter output integrated jitter close to 1.8ps, against the desired 600fs in the frequency range of interest. This excessive jitter resulted in catastrophic failure of both EH and VEC. This paper provides a summary of the technical challenges, key findings, and decisions taken during the debug to make the product spec compliant in the end.