Passive transmission line equalization using circuit-board thru-holes

A method of tuning the impedance characteristics of a high-speed signaling trace embedded in a multi-conductive-layer circuit board, the method comprising:

• routing the high-speed signaling trace across the board between upper and lower ground planes, the trace separated from the upper and lower ground planes by a dielectric material of a substantially uniform thickness along the length of the trace;
• at the ends of the trace, connecting the trace respectively to first and second signaling thru-holes used to inject signals at one end of the trace and receive signals at the other end of the trace, each thru-hole having a conductive liner that passes through respective clearances in a plurality of conductive planes, including the upper and lower ground planes;
• placing a first conductive pad on a first selected one of the conductive planes, the first pad having a clearance separating that pad from the remainder of the selected conductive plane;
• and
• passing the first signaling thru-hole through the selected conductive plane in an alignment that intersects the first conductive pad.

An electrical router backplane comprising:

• multiple high-speed signaling layers, each high-speed signaling layer comprising a plurality of high-speed differential trace pairs with an individual trace width of approximately 7 to 9 mils and a differential trace spacing of 15 to 20 mils, sandwiched between layers of a dielectric material, each trace having a conductive pad at each end;
• a plurality of ground planes, including ground planes interposed respectively between the high-speed signaling layers, the trace-to-ground-plane spacing related to the differential trace spacing and the individual trace width such that the impedance of individual high-speed differential traces is marginally more differential than single-ended;
• a plurality of signaling thru-holes, each having a conductive liner electrically connected to and passing through a conductive pad at one end of a high-speed differential trace, respectively;
• and
• conductive pads at the respective locations of the signaling thru-holes on a plural subset of the ground planes, each separated by a clearance from the remainder of the ground plane they reside on, the signaling thru-holes electrically connected to and passing through the conductive pads at their respective locations.