Crosstalk analysis for varying degree of in-pair coupling in coupled differential pairs

Differentially-routed traces on printed circuit boards typically incorporate loose in-pair coupling when compared to the coupling between the traces and the ground planes. Loose coupling facilitates in-pair skew correction without affecting the differential-mode impedance. However, practical channels combine printed circuit boards with other components that have different degrees of in-pair coupling which could affect the crosstalk among adjacent pairs. This paper examines the effects of different degrees of in-pair coupling on near end crosstalk in the absence of in-pair skew. The analysis will help printed circuit board designers to choose the desired degree of in-pair coupling to achieve targeted near end crosstalk performance.