Reduction of common-mode excitation on a differential transmission line bend by imbalance control

Abstract

Asymmetry in a differential transmission line bend generates a large common mode, which leads to signal integrity issues. Herein two methods are proposed to improve the symmetry and reduce the common-mode at the line bend on a printed circuit board. Placing a guard trace near a narrowed inner signal line at the line bend results in a 15-dB reduction of the common mode. Alternatively, employing a stub connected to the inner signal at the bend section results in a more than 20-dB reduction.