Common mode rejection in differential pairs using slotted ground planes
AssigneeTexas Instruments Incorporated
InventorsGregory Eric Howard, Leland Swanson
Life of this patent
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Abstract
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.
Claims26
A substrate comprising:
- a differential pair transmission line;
- an equi-potential plane with slots formed in the equi-potential plane, wherein the slots lie beneath the differential pair transmission line and are disposed perpendicularly to the differential pair transmission line's orientation;
- and
- a dielectric layer positioned between the differential pair transmission line and the slotted equi-potential plane, the dielectric layer to electrically insulate the differential pair transmission line from the equi-potential plane.
A semiconductor chip comprising:
- a substrate comprising:
- a differential pair transmission line;
- an equi-potential plane with slots formed in the equi-potential plane, wherein the slots lie beneath the differential pair transmission line and are disposed perpendicularly to the differential pair transmission line's orientation;
- a dielectric layer positioned between the differential pair transmission line and the slotted equi-potential plane, the dielectric layer to electrically insulate the differential pair transmission line from the equi-potential plane;
- and
- the semiconductor chip further comprising a package to hold the substrate, the package comprising a pad coupled to a pin on the package, the pad to provide electrical connectivity between the pin and the differential pair transmission line.
A method for forming a slotted ground plane comprising:
- forming an equi-potential plane;
- forming slots in the equi-potential plane, such that the slots run perpendicular to a differential pair transmission line;
- forming a dielectric layer on the equi-potential plane;
- and
- forming the differential pair transmission lines on the dielectric layer.
Dependencies are inferred from the claim text.