ICS844256AM datasheet(9/13 Pages) ICST

9 / 13 page

844256AM

www.icst.com/products/hiperclocks.html

REV. A NOVEMBER 29, 2005

Integrated

Circuit

Systems, Inc.

ICS844256

FEMTOCLOCKS™CRYSTAL-TO-LVDS

FREQUENCY SYNTHESIZER W/INTEGRATED FANOUT BUFFER

PRELIMINARY

As in any high speed analog circuitry, the power supply

pins are vulnerable to random noise. The ICS844256 pro-

vides separate power supplies to isolate any high switch-

ing noise from the outputs to the internal PLL. V

DD, VDDA and

DDO 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

resistor along with a 10

μF and a .01μF bypass capacitor

should be connected to each V

DDA pin. The 10Ω resistor

can also be replaced by a ferrite bead.

POWER SUPPLY FILTERING TECHNIQUES

FIGURE 1. POWER SUPPLY FILTERING

DDA

μF

.01

μF

3.3V

.01

μF

APPLICATION INFORMATION

CRYSTAL INPUT INTERFACE

The ICS844256 has been characterized with 18pF parallel

resonant crystals. The capacitor values shown in Figure 2

Figure 2. CRYSTAL INPUt INTERFACE

below were determined using an 18pF parallel resonant crys-

tal and were chosen to minimize the ppm error.

18p

18pF Parallel Crystal

22p

XTAL_IN

XTAL_OUT

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