Patent ID: 8253509

Claim:
A printed circuit board comprising: a signal layer comprising a pair of differential transmission lines; and a ground layer adjacent to the signal layer, comprising a first void, a second void, a third void, and a common mode filter, wherein the first void and the second void are respectively arranged at opposite sides of a projection of the pair of differential transmission lines on the ground layer, and are bridged via the third void, and wherein the common mode filter comprises: a first filter portion positioned in the first void; and a second filter portion positioned in the second void; wherein each of the first and second filter portions comprises a first and a second coils arranged side by side along a direction parallel to the projection of the pair of differential transmission lines; and wherein the third void communicates with the first and second voids, each the first and second coils of the first and second filter portions are arranged at opposite sides of the third void and non-symmetrical along the third void, one end of the third void is defined between two points where the first and second coils in the first void are connected to the ground layer, the other end of the third void is defined between two points where the first and second coils in the second void are connected to the ground layer.