US Patent 8013255 Printed circuit board with high density differential pairs

An exemplary PCB includes a first reference layer, a first signal layer, and a second signal layer in that order. A first differential pair is arranged in the first signal layer in an edge-coupled structure referencing the first reference layer. A second differential pair is arranged in the second signal layer in edge-coupled structure. A first ground part and a second ground part are symmetrically arranged in the second signal layer and at opposite sides of the second differential pair. The first differential pair is arranged above the first ground part such that a projection of the first differential pair onto the second signal layer having an area coincident with the first ground part. The second differential pair references the first and second ground parts.