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 at opposite sides of the second differential pair in the second signal layer. The first differential pair is arranged above the first ground part and 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.