Timing-Safe Spread Spectrum EMI Reduction

Spread spectrum electromagnetic interference (EMI) reduction is a technique in which the frequency of a clock signal is increased or decreased gradually, and then brought back to its original frequency. By "spreading" electromagnetic energy over a narrow band of the frequency spectrum, the energy spikes of the frequencies and harmonics are smoothed over, hence reducing EMI. The technique is effective when applied to systems where a single master clock acts as the source of the system timing and all other clock and data signals derive their timing from this source. However, it can invite data synchronization problems when attempts are made to use this technique directly on selected independent sub-system clocks.