参数资料
型号: ICS8427BK-02
厂商: INTEGRATED DEVICE TECHNOLOGY INC
元件分类: XO, clock
英文描述: 700 MHz, OTHER CLOCK GENERATOR, QCC32
封装: 5 X 5 MM, 0.75 MM HEIGHT, MO-220, VFQFN-32
文件页数: 4/19页
文件大小: 280K
代理商: ICS8427BK-02
8427BY-02
www.icst.com/products/hiperclocks.html
REV. A MARCH 4, 2005
12
PRELIMINARY
Integrated
Circuit
Systems, Inc.
ICS8427-02
700MHZ, LOW JITTER
LVCMOS/CRYSTAL-TO-LVHSTL FREQUENCY SYNTHESIZER
Spread-spectrum clocking is a frequency modulation tech-
nique for EMI reduction. When spread-spectrum is enabled, a
30KHz triangle waveform is used with 0.5% down-spread
(+0.0% / -0.5%) from the nominal 200MHz clock frequency.
An example of a triangle frequency modulation profile is shown
in
Figure 5A below. The ramp profile can be expressed as:
Fnom = Nominal Clock Frequency in Spread OFF mode
(200MHz with 16.66MHz IN)
Fm = Nominal Modulation Frequency (30KHz)
δ = Modulation Factor (0.5% down spread)
(1 -
δ) fnom + 2 fm x δ x fnom x t when 0 < t <
,
(1 -
δ) fnom - 2 fm x δ x fnom x t when
< t <
1
2 fm
1
2 fm
1
fm
The ICS8427-02 triangle modulation frequency deviation will
not exceed 0.6% down-spread from the nominal clock fre-
quency (+0.0% / -0.5%). 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 5B. The ratio of this
width to the fundamental frequency is typically 0.4%, and will
not exceed 0.6%. The resulting spectral reduction will be
greater than 7dB, as shown in Figure 5B. It is important to
note the ICS8427-02 7dB minimum spectral reduction is the
component-specific EMI reduction, and will not necessarily
be the same as the system EMI reduction.
FIGURE 5B. 200MHZ CLOCK OUTPUT IN FREQUENCY DOMAIN
(A) SPREAD-SPECTRUM OFF
(B) SPREAD-SPECTRUM ON
FIGURE 5A. TRIANGLE FREQUENCY MODULATION
SPREAD SPECTRUM
Δ 10 dBm
δ = .4%
B
A
Fnom
(1 -
δ) Fnom
0.5/fm
1/fm
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