FEMTOCLOCK® CRYSTAL-TO-3.3V LVPECL CLOCK GENERATOR 6 Rev D 9/25/15
843021 DATA SHEET
Applications Information
Power Supply Filtering Technique
As in any high speed analog circuitry, the power supply pins are
vulnerable to random noise. To achieve optimum jitter performance,
power supply isolation is required. The 843021 provides separate
power supplies to isolate any high switching noise from the outputs
to the internal PLL. V
CC
and V
CCA
should be individually connected
to the power supply plane through vias, and 0.01µF bypass
capacitors should be used for each pin. Figure 1 illustrates this for a
generic V
CC
pin and also shows that V
CCA
requires that an additional
10 resistor along with a 10F bypass capacitor be connected to the
V
CCA
pin.
Figure 1. Power Supply Filtering
Crystal Input Interface
The 843021 has been characterized with 18pF parallel resonant
crystals. The capacitor values, C1 and C2, shown in Figure 2 below
were determined using a 25MHz, 18pF parallel resonant crystal and
were chosen to minimize the ppm error. The optimum C1 and C2
values can be slightly adjusted for different board layouts.
Figure 2. Crystal Input Interface
XTAL_IN
XTAL_OUT
X1
18pF Parallel Crystal
C1
33pF
C2
27pF
