From cell phones to scanners, PDAs to printers, and video game consoles to voice recorders, USB ports are everywhere. With the release of high-speed USB 2.0, more and more manufacturers are incorporating USB ports into all types of devices.

With these advances also comes the increased problem of electromagnetic interference (EMI) and additional challenges meeting FCC compliance. Traditional “passive” methods of reducing EMI in USBs—such as Common Mode Chokes (CMCs)—have been popular. However, they are not as effective as “active” measures—such as spread spectrum clocking (SSC)—in preserving signal integrity and saving valuable printed circuit board space. Despite USB compliance standards and tests imposing very tight timing and frequency domain limits, SSC has become a viable alternative for USB applications.