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參數資料
| 型號： | W48S87 |
| 廠商： | Cypress Semiconductor Corp. |
| 英文描述： | Spread Spectrum 3 DIMM Desktop Clock |
| 中文描述： | 擴頻3個DIMM桌面時鐘 |
| 文件頁數： | 4/19頁 |
| 文件大小： | 248K |
| 代理商： | W48S87 |
W48S87-72
4
Spread Spectrum Generator
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 1
.
As depicted in
Figure 1
, 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 num-
ber and the frequency deviation or spread. The equation for
the reduction is
dB = 6.5 + 9*log
10
(P) + 9*log
10
(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 2
. 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 ±0.5% of the center frequen-
cy.
Figure 2
details the Cypress spreading pattern. Cypress
does offer options with more spread and greater EMI reduc-
tion. Contact your local Sales representative for details on
these devices.
Spread Spectrum clocking is activated or deactivated by se-
lecting the appropriate values for bits 1
–
0 in data byte 0 of the
I
2
C data stream. Refer to
Table 4
for more details.
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66
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6SUHDG
6SHFWUXP
(QDEOHG
(0, 5HGXFWLRQ
6SHFWUXP
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66
Figure 1. Clock Harmonic with and without SSCG Modulation Frequency Domain Representation
Figure 2. Typical Modulation Profile
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
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相關代理商/技術參數 |
參數描述 |
|---|---|
| W48S87-04 | 制造商:CYPRESS 制造商全稱:Cypress Semiconductor 功能描述:Spread Spectrum 3 DIMM Desktop Clock |
| W48S87-72 | 制造商:CYPRESS 制造商全稱:Cypress Semiconductor 功能描述:Desktop/Notebook Frequency Generator |
| W48S87-72H | 制造商:Cypress Semiconductor 功能描述:Logic and Timing, Clock Generation, Desktop/Notebook Frequency Generator |
| W48S87-72XT | 制造商:Rochester Electronics LLC 功能描述:- Tape and Reel |
| W49 | 制造商:CERAMATE 制造商全稱:CERAMATE 功能描述:3-Phase Motor Driver for CD-ROMs |
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