Noise Coupling Mechanism Analysis and Mitigation Method for Receiver Sensitivity Improvement in an Optical QSFP Transceiver Module

The increasingly growth of the traffic in data centers demands for high-speed data transition and high bandwidth density. Optical communication is a promising way for the propagation of high-speed signals with less distortions. The quad small form-factor pluggable (QSFP) transceiver module is an essential component converting an electrical signal into an optical signal for point-to-point data transition. Considerable attentions have been paid to the signal integrity (SI) optimization for the optical QSFP transceiver modules with different data rates, where the receiver sensitivity is generally considered to be critical. In this paper, the receiver sensitivity problem of a typical QSFP transceiver module with 10 Gbit/s data rate is studied. It is the first time to demonstrate that the receiver sensitivity improvement is not only related with the SI design, but also connected with the electromagnetic interference (EMI) mitigation inside the DUT. The convential simulation model used for SI analysis with important metal configurations excluded is limited in the ability to identify the coupling between the radiating structures. It is found that the EMI noise induced by the unbalanced PCB routing and the interconnect between the PCB and flexible printed circuit (FPC) has significant contribution to the total noise at the receiver end. The generation of the antenna-mode current is verified and further studied using the full wave simulations. The mitigation method is proposed and confirmed through the measurements to improve the receiver sensitivity.