High-speed USB PCB Layout Recommendations.pdf

High-speed USB PCB Layout mendations
Introduction When two microstrips run parallel to each other cross-cou-
pling occurs. The space between the microstrips (S) as relat-
High-speed USB operates at 480 Mbps with 400-mV signal- ed to their height above a plane (H) affects the amount of
ing. For patibility, devices that are high-speed cross-coupling that occurs. The amount of cross-coupling in-
capable must also be able municate with existing full- creases as the space between the microstrips is reduced. As
speed USB products at 12 Mbps with signaling. High- cross-coupling increases the microstrips’ impedances de-
speed USB hubs are also required to talk to low-speed prod-
crease. Differential impedance, Zdiff, is measured by measur-
ucts at Mbps. Designing printed circuit boards (PCBs) that ing the impedance of both microstrips and summing them.
meet these requirements can be challenging.
High-speed USB is defined in the Universal Serial Bus Spec-
ification Revision , located at . The or- WWS
ganization that oversees the specification is the USB Imple-
menters Forum. The USB-IF requires that all devices receive T
testing to pliance to the specification and to ensure
ε
interoperability with other devices. Cypress mends that r H
designers pre-test their products for pliance before
attending a pliance Workshop.
This application note details guide