Backplane with power plane having a digital ground structure in signal regions

1. A modular router comprising:

at least two line cards to receive and transmit packets external to the router;

an electrical backplane having slots for each of the line cards, each slot comprising at least one power connector region and at least one high-speed connector region, the power connector region supplying operating power to the line card in that slot from power planes embedded in the backplane, the high-speed connector region providing electrical connections from the line card in that slot to high-speed signaling traces in the backplane, the electrical connections passing through at least one of the power planes through clearances in a conductive plane section that is electrically connected to digital ground and not to a power supply section of that power plane.

2. The modular router of claim 1 , each of the power planes having a thickness at least as thick as an equivalent layer of three-ounce copper.

3. The modular router of claim 1 , further comprising a plurality of digital ground plane layers, wherein the electrical connection clearances in the first conductive plane section are of a size that allows high-speed signaling to be routed through the power planes with approximately the same impedance as where the high-speed signaling electrical connections pass through the digital ground plane layers.

4. The modular router of claim 1 , wherein the conductive plane section completely surrounds each high-speed electrical connection in the high-speed connector region, the conductive plane section separated from each high-speed electrical connection by a respective one of the clearances.

5. A method of fabricating high-speed signal paths in an electrical backplane, the method comprising:

embedding multiple power planes in the backplane, the multiple power planes having the capability to power components connected to the backplane through at least one power connector region;

routing a group of high-speed signals through the multiple power planes in a high-speed connector region comprising a plurality of conductive high-speed signaling throughholes and at least one conductive digital ground throughhole;

for each power plane, forming a clearance between a first conductive plane section in the high-speed connector region and a power supply section of the power plane;

for each first conductive plane section, forming a clearance between the first conductive plane section and each of the high-speed signaling throughholes in the high-speed connector region; and

for each first conductive plane section, connecting the conductive plane section to at least one of the digital ground throughholes.

6. The method of claim 5 , further comprising setting the clearance between the first conductive plane section and each of the high-speed signaling throughholes such that the impedance of each high-speed signaling throughhole is approximately equal in the power plane region of the backplane as in other layer regions of the backplane.

7. The method of claim 5 , further comprising grouping the power planes together between digital ground planes.

8. The method of claim 7 , further comprising arranging four power planes to function as a first primary power plane, a first primary power return plane, a second primary power plane, and a second primary power return plane.

9. The method of claim 5 , further comprising, for at least one digital ground throughhole connected to the first conductive plane section of a power plane, also connecting that digital ground throughhole to the digital ground planes.