FemtoClock

Frequency Synthesizer With/Integrated Fanout Buffer

843256 DATA SHEET

8

REVISION B 12/18/14

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

vulnerable to random noise. The 843256 provides separate power

supplies to isolate any high switching noise from the outputs to the

internal PLL. V

CC

, V

CCA

, and V

CCO

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 10

μF and a .01μF bypass capacitor should be con-

nected to each V

CCA

pin.

10

Ω

V

CCA

10

μF

.01

μF

3.3V

.01

μF

V

CC

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.

All unused LVPECL outputs can be left floating. We recommend

that there is no trace attached. Both sides of the differential output

pair should either be left floating or terminated.

C1

18p

X1

18pF Parallel Crystal

C2

22p

XTAL_IN

XTAL_OUT

The 843256 has been characterized with 18pF parallel resonant

crystals. The capacitor values shown in Figure 2 below were

deter mined using an 18pF parallel resonant cr ystal and

were chosen to minimize the ppm error.