The effects of reference capacitors on signal transmission through single-ended traces in multi-layer PCBs

In a high-speed multi-layer PCB (printed circuit board) design with multiple logic voltage levels, signal trace placement can be an important issue. Single-ended high-speed signals that use the power layers as reference (return) may suffer increased losses in some frequency ranges due to the displacement current path from the power layer to ground. "Reference" capacitors are recommended as a solution to mitigate this effect. The frequency ranges where the increased losses occur are demonstrated to be ranges containing board distributed resonance frequencies. The effects of the number and locations of reference capacitors on signal transmission are also studied, and reported in this paper.