ICS844003I datasheet(9/13 Pages) ICST

9 / 13 page

844003AGI

www.icst.com/products/hiperclocks.html

REV. B AUGUST 25, 2005

Integrated

Circuit

Systems, Inc.

ICS844003I

FEMTOCLOCKS™CRYSTAL-TO-LVDS

FREQUENCY SYNTHESIZER

PRELIMINARY

APPLICATION INFORMATION

CRYSTAL INPUT INTERFACE

The ICS844003I has been characterized with 18pF parallel

resonant crystals. The capacitor values shown in Figure 3 below

Figure 3. CRYSTAL INPUt INTERFACE

were determined using a 31.25MHz or 26.041666MHz 18pF paral-

lel resonant crystal and were chosen to minimize the ppm error.

ICS844003I

POWER SUPPLY FILTERING TECHNIQUES

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

are vulnerable to random noise. The ICS844003I provides

separate power supplies to isolate any high switching

noise from the outputs to the internal PLL. V

DD, VDDA, and VDDOx

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 10

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

capacitor should be connected to each V

DDA pin. The 10Ω

resistor can also be replaced by a ferrite bead.

FIGURE 2. POWER SUPPLY FILTERING

DDA

μF

.01

μF

3.3V

.01

μF

22p

18pF Parallel Crystal

22p

XTAL_OUT

XTAL_IN

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