Systematic Crosstalk Reduction Methods towards PCIe 7.0 PAM4 Transmission on Lopro FPIO Connectors

Crosstalk has emerged as a critical challenge in 5G/6G-connector data links and led to severe inter-channel interference in high-speed communication performance. In this work, we develop a systematic signal integrity pathfinding method to improve the 4-port differential S-parameters performance and result in enhancing the Pulse Amplitude Modulation 4-level (PAM4) eye diagram quality. This method includes anti-nodal airbridge placement and lateral scaling of the spacing between differential pairs. When applied to the Peripheral Component Interconnect Express (PCIe) Low-profile Fast-Pass Input/Output (Lopro FPIO) connectors, the approach effectively mitigates differential signal insertion loss and reduces crosstalk degradation to meet the PCIe 6.0 specifications. The crosstalk of near-end crosstalk (NEXT) and far-end crosstalk (FEXT) improves by 32 dB and 30 dB respectively at the first resonant frequency (12.75GHz). For PCIe 6.0 at 64-GT/s PAM4 signaling, this pathfinding method demonstrates improvements of 15% in average eye height (EH) and 9% in average eye width (EW). At 128-GT/s PAM4, the enhancements reach 175% for average EH and 75% for average EW, providing a viable solution for the next-generation PCIe 7.0 applications.