ICS843004 datasheet(9/16 Pages) ICST

9 / 16 page

843004AG

www.icst.com/products/hiperclocks.html

REV. A NOVEMBER 18, 2004

Integrated

Circuit

Systems, Inc.

ICS843004

FEMTOCLOCKS™LVCMOS/CRYSTAL-TO-

3.3V LVPECL FREQUENCY SYNTHESIZER

APPLICATION INFORMATION

As in any high speed analog circuitry, the power supply pins

are vulnerable to random noise. The ICS843004 provides sepa-

rate power supplies to isolate any high switching

noise from the outputs to the internal PLL. V

CC, VCCA, and VCCO

should be individually connected to the power supply

plane through vias, and bypass capacitors should be

used for each pin. To achieve optimum jitter performance,

power supply isolation is required.

Figure 1 illustrates how

a 10

Ω resistor along with a 10µF and a .01µF bypass

capacitor should be connected to each V

CCA.

POWER SUPPLY FILTERING TECHNIQUES

FIGURE 1. POWER SUPPLY FILTERING

Ω

CCA

µF

.01

µF

3.3V

.01

µF

TERMINATION FOR 3.3V LVPECL OUTPUT

CC - 2V

Ω

RTT

o = 50Ω

FOUT

FIN

RTT =

((V

OH + VOL) / (VCC – 2)) – 2

3.3V

125

Ω

125

Ω

o = 50Ω

FOUT

FIN

The clock layout topology shown below is a typical termi-

nation for LVPECL outputs. The two different layouts men-

tioned are recommended only as guidelines.

FOUT and nFOUT are low impedance follower outputs that

generate ECL/LVPECL compatible outputs. Therefore, ter-

minating resistors (DC current path to ground) or current

sources must be used for functionality. These outputs are

FIGURE 2B. LVPECL OUTPUT TERMINATION

FIGURE 2A. LVPECL OUTPUT TERMINATION

designed to drive 50

Ω transmission lines. Matched imped-

ance techniques should be used to maximize operating

frequency and minimize signal distor tion.

Figures 2A and

2B show two different layouts which are recommended

only as guidelines. Other suitable clock layouts may exist

and it would be recommended that the board designers

simulate to guarantee compatibility across all printed cir-

cuit and clock component process variations.

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