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W180 Datasheet(PDF) 4 Page - Cypress Semiconductor

Part No. W180
Description  Peak Reducing EMI Solution
Download  10 Pages
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Manufacturer  CYPRESS [Cypress Semiconductor]
Direct Link  http://www.cypress.com
Logo CYPRESS - Cypress Semiconductor

W180 Datasheet(HTML) 4 Page - Cypress Semiconductor

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W180
Document #: 38-07156 Rev. *B
Page 4 of 10
Spread Spectrum Frequency Timing
Generation
The device generates a clock that is frequency modulated in
order to increase the bandwidth that it occupies. By increasing
the bandwidth of the fundamental and its harmonics, the ampli-
tudes of the radiated electromagnetic emissions are reduced.
This effect is depicted in Figure 2.
As shown in Figure 2, a harmonic of a modulated clock has a
much lower amplitude than that of an unmodulated signal. The
reduction in amplitude is dependent on the harmonic number
and the frequency deviation or spread. The equation for the
reduction is:
dB = 6.5 + 9*log10(P) + 9*log10(F)
Where P is the percentage of deviation and F is the frequency
in MHz where the reduction is measured.
The output clock is modulated with a waveform depicted in
Figure 3. This waveform, as discussed in “Spread Spectrum
Clock Generation for the Reduction of Radiated Emissions” by
Bush, Fessler, and Hardin produces the maximum reduction
in the amplitude of radiated electromagnetic emissions.
Figure 3 details the Cypress spreading pattern. Cypress does
offer options with more spread and greater EMI reduction.
Contact your local Sales representative for details on these
devices.
SSFTG
Typical Clock
Frequency Span (MHz)
Center Spread
Spread
Spectrum
Enabled
EMI Reduction
Spread
Spectrum
Non-
Frequency Span (MHz)
Down Spread
Figure 2. Clock Harmonic with and without SSCG Modulation Frequency Domain Representation
MAX.
MIN.
Figure 3. Typical Modulation Profile


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