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ICS844256BG REV. B NOVEMBER 19, 2007

ICS844256

FEMTOCLOCKS™ CRYSTAL-TO-LVDS FREQUENCY SYNTHESIZER W/INTEGRATED FANOUT BUFFER

PRELIMINARY

10

Ω

V

DDA

10

μF

.01

μF

3.3V

.01

μF

V

DD

The ICS844256 has been characterized with 18pF parallel

resonant crystals. The capacitor values shown in Figure 2

below were deter mined using an 18pF parallel resonant

crystal and were chosen to minimize the ppm error.

C1

18p

X1

18pF Parallel Crystal

C2

22p

XTAL_IN

XTAL_OUT

All control pins have internal pull-ups or pull-downs; additional

resistance is not required but can be added for additional

protection. A 1k

Ω resistor can be used.

LVDS Outputs

All unused LVDS output pairs can be either left floating or

terminated with 100

Ω across. If they are left floating, we

recommend that there is no trace attached.

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

vulnerable to random noise. To achieve optimum jitter perfor-

mance, power supply isolation is required. The ICS844256 pro-

vides separate power supplies to isolate any high switching noise

from the outputs to the internal PLL. V

be individually connected to the power supply plane through vias,

and 0.01µF bypass capacitors should be used for each pin. Fig-

ure 1 illustrates this for a generic V

V

bypass capacitor be connected to the V