Effects of power bus stitching on signal integrity and thermal analysis

Ferrite beads and gaps are commonly used to isolate simultaneous switching noise produced on the power/ground planes of the modern digital boards by the switching of complex integrated circuits. The work presented in this paper studies the effectiveness of these components in mitigating the propagation of the high-frequency noise on DC power buses of a very complex multilayer high speed digital board. Two different types of ground plane layouts are compared: single point and multipoint ground layer stitching. S₂₁ measurements on bare boards and eye diagram measurements on full functioning boards show a better degree of isolation in the case of multipoint ground plane stitching. The signal integrity analysis is integrated with a thermal analysis, conducted with infrared thermographies executed on the test boards. Three points are explained in details: 1) plane segmentation improves noise separation; 2) multipoint stitching improves thermal dissipation; 3) power plane segmentation together with ground plane stitching is a good compromise between electrical and thermal demands