ICS844002 datasheet(8/16 Pages) IDT

8 / 16 page

IDT™ / ICS™ LVDS FREQUENCY SYNTHESIZER

ICS844002AG REV. A SEPTEMBER 28, 2007

ICS844002

FEMTOCLOCKS™ CRYSTAL-TO-LVDS FREQUENCY SYNTHESIZER

APPLICATION INFORMATION

CRYSTAL INPUT INTERFACE

The ICS844002 has been characterized with 18pF parallel

resonant crystals. The capacitor values shown in Figure 2 below

Figure 2. CRYSTAL INPUt INTERFACE

were determined using a 26.5625MHz, 18pF parallel resonant

crystal and were chosen to minimize the ppm error.

POWER SUPPLY FILTERING TECHNIQUES

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

are vulnerable to random noise. The ICS844002 provides sepa-

rate power supplies to isolate any high switching noise from

the outputs to the internal PLL. V

DD, VDDA, and VDDO 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

0.01

μF bypass capacitor should be connected to each V

DDA pin.

FIGURE 1. POWER SUPPLY FILTERING

DDA

μF

.01

μF

3.3V or 2.5V

.01

μF

33p

18pF Parallel Crystal

27p

XTAL_OUT

XTAL_IN

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