ICS84314AY-02LF 查看數據表（PDF） - Integrated Circuit Systems

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ICS84314AY-02LF

700MHZ, CRYSTAL-TO-3.3V/2.5V LVPECL FREQUENCY SYNTHESIZER W/FANOUT BUFFER

Integrated Circuit Systems 

Integrated

Circuit

Systems, Inc.

PRELIMINARY

ICS84314-02

700MHZ, CRYSTAL-TO-3.3V/2.5V LVPECL

FREQUENCY SYNTHESIZER W/FANOUT BUFFER

SPREAD SPECTRUM

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 7A below. The ramp profile can be expressed as:

• Fnom = Nominal Clock Frequency in Spread OFF mode

(200MHz with 16MHz 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

<

2

1

fm

,

(1

-

δ)

fnom

-

2

fm

x

δ

x

fnom

x

t

when2

1

fm

<

t

<

1

fm

The ICS84314-02 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 7B. 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 7B. It is impor-

tant to note the ICS84314-02 7dB minimum spectral reduc-

tion is the component-specific EMI reduction, and will not

necessarily be the same as the system EMI reduction.

Fnom

Δ − 10 dBm

B

A

(1 - δ) Fnom

0.5/fm

1/fm

FIGURE 6A. TRIANGLE FREQUENCY MODULATION

δ = 0.4% ➤

➤

FIGURE 6B. 200MHZ CLOCK OUTPUT IN FREQUENCY DOMAIN

(A) SPREAD-SPECTRUM OFF

(B) SPREAD-SPECTRUM ON

84314AY-02

www.icst.com/products/hiperclocks.html

14

REV. B NOVEMBER 17, 2005

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