Effect of shield insertion on reducing crosstalk noise between coupled interconnects

Placing shields around a victim signal line is a common way to enhance signal integrity while minimizing delay uncertainty. For two coupled interconnects with a shield between the lines, the coupling noise can produce a peak noise of 15% of V_dd in a 0.18 μm CMOS technology. A pseudo-2π RC model is used to develop an analytic estimate of the peak noise for shielded interconnects. The peak noise model is accurate within an average error of 4.4% as compared to SPICE. The effects of the shield width, length, separation between the shield and the signal, and the number of connections tieing the shield to ground on the overall crosstalk noise are described in this paper. Based on the peak noise model, a minimum number of ground connections for a target shield line with noise constraints is obtained. Inserting a shield line between two coupled interconnects is shown to be more effective in reducing crosstalk noise than increasing the physical separation.