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參數資料
| 型號： | W42C32 |
| 廠商： | Cypress Semiconductor Corp. |
| 英文描述： | Spread Spectrum Frequency Timing Generator |
| 中文描述： | 擴頻頻率定時發生器 |
| 文件頁數： | 4/8頁 |
| 文件大小： | 131K |
| 代理商： | W42C32 |
W42C32-05
4
Spread Spectrum Frequency Timing
Generation
The benefits of using Spread Spectrum Frequency Timing
Generation are depicted in
Figure 2
. An EMI emission profile
of a clock harmonic is shown.
Contrast the typical clock EMI with the Cypress spread spec-
trum clock. 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 Cypress
’
s
Spread Spectrum Frequency Timing Generator (SSFTG), the
peak energy is much lower (at least 8 dB) because the energy
is spread out across a wider bandwidth.
Modulating Waveform
The shape of the modulating waveform is critical to EMI reduc-
tion. The modulation scheme used to accomplish the maxi-
mum reduction in EMI is shown in
Figure 3
. The period of the
modulation is shown as a percentage of the period length
along the X axis. The amount that the frequency is varied is
shown along the Y axis, also shown as a percentage of the
total frequency spread.
Cypress frequency selection tables express the modulation
percentage in two ways. The first method displays the spread-
ing frequency band as a percent of the programmed average
output frequency, symmetric about the programmed average
frequency. This method is always shown using the expression
f
Center
±
X
MOD
% in the frequency spread selection table.
The second approach is to specify the maximum operating
frequency and the spreading band as a percentage of this fre-
quency. The output signal is swept from the lower edge of the
band to the maximum frequency. The expression for this ap-
proach is f
MAX
–
X
MOD
%. Whenever this expression is used,
Cypress has taken care to ensure that f
MAX
will never be ex-
ceeded. This is important in applications where the clock
drives components with tight maximum clock speed specifica-
tions.
SSFTG
Typical Clock
5dB/div
A
Figure 2. Typical Clock and SSFTG Comparison
100%
80%
60%
40%
20%
0%
–
20%
–
40%
–
60%
–
80%
–
100%
1
2
3
4
5
6
7
8
9
1
1
2
3
4
5
6
7
8
9
1
Time
F
Figure 3. Modulation Waveform Profile
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相關代理商/技術參數 |
參數描述 |
|---|---|
| W42C32-05 | 制造商:CYPRESS 制造商全稱:Cypress Semiconductor 功能描述:Spread Spectrum Frequency Timing Generator |
| W42C32-05MG | 制造商:Cypress Semiconductor 功能描述:PREMIS EMI REDUCTION SSCGS |
| W42C32-05MGT | 制造商:Cypress Semiconductor 功能描述:DRIVER-CLOCK DRIVER |
| W42C70-01G | 制造商:未知廠家 制造商全稱:未知廠家 功能描述:IC-SM-ZERO DELAY BUFFER |
| W42WUM/EGW | 制造商:Kingbright Corporation 功能描述:LED Bi-Color Green/Red 565nm/627nm 2-Pin |
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