ICS843242 datasheet(8/16 Pages) IDT

8 / 16 page

IDT™ / ICS™ 3.3V LVPECL FREQUENCY SYNTHESIZER

ICS843242AG REV. A OCTOBER 2, 2007

ICS843242

FEMTOCLOCKS™ CRYSTAL-TO-3.3V LVPECL FREQUENCY SYNTHESIZER

PRELIMINARY

APPLICATION INFORMATION

CRYSTAL INPUT INTERFACE

The ICS843242 has been characterized with 18pF parallel

resonant crystals. The capacitor values shown in Figure 2

below were determined using a 31.25MHz or 26.041666MHz

FIGURE 2. CRYSTAL INPUt INTERFACE

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 ICS843242 provides

separate power supplies to isolate any high switching

noise from the outputs to the internal PLL. V

CC, VCCA, VCCO_A and

CCO_B 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 0.01μF bypass

capacitor should be connected to each V

CCA pin.

FIGURE 1. POWER SUPPLY FILTERING

CCA

μF

.01

μF

3.3V

.01

μF

33p

18pF Parallel Crystal

27p

XTAL_OUT

XTAL_IN

ICS843242 Datasheet(PDF) 8 Page - Integrated Device Technology