Improving Signal Integrity by Reducing Mode Conversion in Differential Pairs on a Meshed Ground in Flexible Printed Circuit Boards

Abstract

Asymmetry in a differential pair leads to deterioration of signal integrity. Differential pairs on a meshed ground often encounter asymmetry in return current paths. In this paper, we propose an offset mesh as an improved mesh structure that offsets asymmetry between a solid region and an aperture region. The offset mesh mitigates the asymmetry in the conventional mesh structure without additional design elements. The proposed structure has been verified to be effective in reducing mode conversion, intra-pair and inter-pair skews, and characteristic impedance variation in the time and frequency domains. This enables high-density routing of differential pairs.

Keywords

• differential pairs
• flexible printed circuit boards
• impedance
• inter-pair skew
• intra-pair skew
• meshed ground
• mode conversion