USB设计指南

High-speed USB PCB Layout RecommendationsHigh-speed USB PCB Layout Recommendations
Introduction
High-speed USB operates at 480 Mbps with 400-mV signaling. For backwards compatibility, devices that are high-speed capable must also be able to communicate with existing fullspeed USB products at 12 Mbps with 3.3V signaling. Highspeed USB hubs are also required to talk to low-speed products at 1.5 Mbps. Designing printed circuit boards (PCBs) that meet these requirements can be challenging. High-speed USB is defined in the Universal Serial Bus Specification Revision 2.0, located at http://www.usb.org. The organization that oversees the specification is the USB Implementers Forum. The USB-IF requires that all devices receive testing to show compliance to the specification and to ensure interoperability with other devices. Cypress recom