Common mode rejection in differential pairs using slotted ground planes

摘要

In high-speed semiconductor packaging, differential pair transmission lines 605 are used to receive incoming signals carried using differential signaling. Common mode noise can decrease the frequency at which these signals are clocked. The use of slots 620 formed in the ground (or power plane) 609 of the substrate and lying perpendicularly (and equally spaced) underneath the differential pair 605 improves the common mode rejection of the differential pair 605 by increasing the common mode impedance without affecting the differential mode impedance. The use of slots 620 does not require modifications to the packaging, and only minor modifications to the substrate.