W48S101-04 Datasheet, PDF (4/12 Pages) Cypress Semiconductor – Spread Spectrum Motherboard Frequency Generator

PRELIMINARY
W48S101-04
Spread Spectrum Clock Generation
The benefits of using Spread Spectrum Clock Generation are
depicted in Figure 3. An EMI emission profile of a clock har-
monic is shown.
Contrast the typical clock EMI with the Cypress Spread Spec-
trum Clock Generation. Notice the spike in the typical clock.
This spike can make systems fail quasi-peak EMI testing. The
FCC and other regulatory agencies test for peak emissions.
With the Cypress clock, the peak energy is much lower (at
least 8 dB) because the energy is spread out across a wider
bandwidth.
5dB/div
SS FTG
Typical C lock
MAX (+0.5%)
-SS% ^{Frequency Span (MHz)} +SS%
Figure 3. Typical Clock and SSCG Comparison
MIN (–0.5%)
Figure 4. Typical Modulation Profile
4