Method and apparatus for increased routing density on printed circuit boards with differential pairs

Abstract

A method and apparatus for decreasing crosstalk between conductors, particularly differential pairs, that are routed in high-density patterns on printed circuit boards system. In one embodiment of the invention, a single-ended conductor is divided at a first point into two single-ended conductors of equal width, with the two single-ended conductors being routed around and alongside a differential pair of conductors. Equal and opposite noise is coupled onto each branch of the single-ended signal from each side of the differential pair. The two single-ended conductors are rejoined at a second point to form a combined single-ended conductor. Signals traveling along the two separate paths of the single-ended are combined at the second point and noise carried in the respective signals is cancelled. Noise coupled into the differential pair from the two single-ended paths is eliminated at the receiving end as common mode noise. In other embodiments of the present invention, the single-ended conductors and the differential pairs are oriented between two planes in stripline or dual stripline configurations. The method and apparatus of the present invention can be implemented in numerous media, such as vias and cables (including flex and ribbon).