Spread Spectrum Clocks are devices that actively suppress emissions. By spreading or modulating the clock signal, the peak energy of the clock signal is distributed. The emission peaks are lowered by a predictable amount so that the end product can pass EMI certification limits. Signal integrity is not affected by using onsemi Spread Spectrum Clocks. In Figure A, an un-modulated 40 MHz clock signal is shown. All pulses are of the same width. Below, the energy peaks at 40 MHz and at the 80 MHz and 120 MHz harmonics. In Figure B, a modulated 40 MHz clock signal is shown. Notice that the widths of the pulses for the spread clock vary. That is, at a given moment users may get 39 MHz or 41 MHz, but on average the signal will still exhibit a frequency of 40 MHz. Now, the energy peaks have been lowered at the 40 MHz and at the harmonics. This is the essence of Spread Spectrum technology. Should a certification require emissions below 35 dB, certification would fail using an un-modulated signal, but would pass using a modulated signal.