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参数资料
| 型号： | W149H |
| 英文描述： | CPU System Clock Generator |
| 中文描述： | CPU系统时钟发生器 |
| 文件页数： | 4/15页 |
| 文件大小： | 151K |
| 代理商： | W149H |
W149
4
Spread Spectrum Clocking
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 am-
plitudes of the radiated electromagnetic emissions are re-
duced. This effect is depicted in
Figure 3
.
As shown in
Figure 3
, 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 4
. 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. The
deviation selected for this chip is either
–
0.5% or ±0.5% of the
selected frequency.
Figure 4
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.
Spread Spectrum clocking cannot be deactivated on the
W149.
Figure 3. Clock Harmonic with and without SSCG Modulation Frequency Domain Representation
SSFTG
Typical Clock
Frequency Span (MHz)
Center Spread
A
MAX (+0.5%)
MIN (
–
0.5%)
1
2
3
4
5
6
7
8
9
1
1
2
3
4
5
6
7
8
9
1
F
Figure 4. Typical Modulation Profile
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相关代理商/技术参数 |
参数描述 |
|---|---|
| W149HT | 制造商:Cypress Semiconductor 功能描述: |
| W14B | 制造商:NSC 制造商全称:National Semiconductor 功能描述:14 Lead Ceramic Flatpack NS Package Number W14B |
| W14B20001-AZZ00-000 | 制造商:Carling Technologies 功能描述:W-SERIES ROCKER SWITCH - Bulk |
| W14B2GJJ1-A79XX-100-XBA1 | 制造商:Carling Technologies 功能描述:W-SERIES ROCKER SWITCH - Bulk |
| W14B2GJJ1-A79XX-100-XCS1 | 制造商:Carling Technologies 功能描述:W-SERIES ROCKER SWITCH - Bulk |
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