Spread Spectrum Clocking Comes to USB
Systems engineers need every weapon at their disposal when electromagnetic interference (EMI) raises its ugly head in USB designs. Passive measures such as ferrite beads or capacitors offer certain benefits, but can adversely affect signal quality and cause USB compliance failure. Implementing spread spectrum clocking (SSC) in USB devices has so far proven difficult, and most engineers have written it off as a means of limiting EMI.
The benefits of SSC are too valuable to be dismissed so quickly, however, especially in a market that continues to demand ever-greater performance, portability, and compatibility in ever-shorter product cycles. This paper challenges assumptions about SSC for USB and explains how, if properly implemented, SSC can recapture its place in the engineer's toolkit.