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| 型号： | 844S012BKI-01LF |
| 厂商： | INTEGRATED DEVICE TECHNOLOGY INC |
| 元件分类： | 时钟产生/分配 |
| 英文描述： | OTHER CLOCK GENERATOR, QCC56 |
| 封装： | 8 X 8 MM, 0.925 MM HEIGHT, ROHS COMPLIANT, MO-220VLLD-2, VFQFN-56 |
| 文件页数： | 9/23页 |
| 文件大小： | 847K |
| 代理商： | 844S012BKI-01LF |
ICS844S012BKI-01 REVISION A APRIL 2, 2010
17
2010 Integrated Device Technology, Inc.
ICS844S012I-01 Data Sheet
CRYSTAL-TO-LVDS/LVCMOS FREQUENCY SYNTHESIZER
Spread Spectrum
Spread-spectrum clocking is a frequency modulation technique for
EMI reduction. When spread-spectrum is enabled, a 32kHz triangle
waveform is used with 0.6% down-spread (+0.0% / -0.6%) from the
nominal output frequency. An example of a triangle frequency
modulation profile is shown in Figure 7A below. The ramp profile can
be expressed as:
Fnom = Nominal Clock Frequency in Spread Off mode
Fm = Nominal Modulation Frequency (30kHz)
δ = Modulation Factor (0.6% down spread)
,
The ICS844S012I-01 triangle modulation frequency deviation will not
exceed 0.7% down-spread from the nominal clock frequency (+0.0%
/ -0.6%). An example of the amount of down spread relative to the
nominal clock frequency can be seen in the frequency domain, as
shown in Figure 7B. The ratio of this width to the fundamental
frequency is typically 0.4%, and will not exceed 0.7%. The resulting
spectral reduction will be greater than 5dB, as shown in Figure 7B. It
is important to note the ICS844S012I-01 5dB minimum spectral
reduction is the component-specific EMI reduction, and will not
necessarily be the same as the system EMI reduction.
Figure 7A. Triangle Frequency Modulation
Figure 7B. 200MHz Clock Output In Frequency Domain
(A) Spread-Spectrum OFF
(B) Spread-Spectrum ON
1
δ
–
(
)Fnom 2Fm δ Fnom t
×
when0 t
1
2Fm
-----------
<<
+
1
δ
–
(
)Fnom 2
– Fm
δ Fnom t
×
when
1
2Fm
----------- t
1
Fm
--------
<<
1/fm
0.5/fm
Fnom
(1 -
δ) Fnom
Frequency
Time
B
A
– 10 dBm
δ = 0.6%
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