US Patent 7880094 Differential signal layout printed circuit board

A positive differential signal trace and a negative differential signal trace are formed on different layers of a printed circuit board. A first ground trace is formed on the layer on which the positive differential signal trace is formed, and a second ground trace is formed on the layer on which the negative differential signal trace is formed. An insulation layer is positioned between the two layers and has a predetermined thickness. A differential mode impedance and a common mode impedance of differential signals are dependent on the predetermined thickness of the insulation layer, width and thickness of each differential signal trace, and a space between each differential signal trace and the corresponding ground trace formed on the same layer.