ICS84325 データシートの表示（PDF） - Integrated Circuit Systems

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ICS84325

CRYSTAL-TO-3.3V LVPECL FREQUENCY SYNTHESIZER WITH FANOUT BUFFER

Integrated Circuit Systems 

Integrated

Circuit

Systems, Inc.

ICS84325

CRYSTAL-TO-3.3V LVPECL

FREQUENCY SYNTHESIZER WITH FANOUT BUFFER

APPLICATION INFORMATION

POWER SUPPLY FILTERING TECHNIQUES

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

are vulnerable to random noise. The ICS84325 provides sepa-

rate power supplies to isolate any high switching

noise from the outputs to the internal PLL. VCC, 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 2 illustrates how

a 24Ω resistor along with a 10µF and a .01µF bypass

capacitor should be connected to each VCCA pin.

VCC

VCCA

3.3V

.01µF 24Ω

.01µF

10 µF

FIGURE 2. POWER SUPPLY FILTERING

TERMINATION FOR LVPECL OUTPUTS

The clock layout topology shown below is a typical termina-

tion for LVPECL outputs. The two different layouts mentioned

are recommended only as guidelines.

FOUT and nFOUT are low impedance follower outputs that

generate ECL/LVPECL compatible outputs.Therefore, terminat-

ing resistors (DC current path to ground) or current sources

must be used for functionality. These outputs are designed to

drive 50Ω transmission lines. Matched impedance techniques

should be used to maximize operating frequency and minimize

signal distortion. Figures 3A and 3B 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

circuit and clock component process variations.

Zo = 50Ω

FOUT

FIN

Zo = 50Ω

50Ω

RTT =

1

((VOH + VOL) / (VCC – 2)) – 2

Zo

50Ω

VCC - 2V

RTT

FOUT

3.3V

125Ω

125Ω

Zo = 50Ω

FIN

Zo = 50Ω

84Ω

84Ω

FIGURE 3A. LVPECL OUTPUT TERMINATION

FIGURE 3B. LVPECL OUTPUT TERMINATION

84325EM

www.icst.com/products/hiperclocks.html

7

REV. B OCTOBER 11, 2004

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