
IDT / ICS 3.3V LVPECL CLOCK GENERATOR
7
ICS843022AG REV A AUGUST 1, 2006
ICS843022
FEMTOCLOCKS CRYSTAL-TO-3.3V LVPECL CLOCK GENERATOR
APPLICATION INFORMATION
Figure 2. CRYSTAL INPUt INTERFACE
CRYSTAL INPUT INTERFACE
The ICS843022 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.
As in any high speed analog circuitry, the power supply pins
are vulnerable to random noise. The ICS843022 provides sepa-
rate power supplies to isolate any high switching
noise from the outputs to the internal PLL. V
CC and VCCA 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
resistor along with a 10F and a .01F bypass
capacitor should be connected to each V
CCA pin.
POWER SUPPLY FILTERING TECHNIQUES
FIGURE 1. POWER SUPPLY FILTERING
10
V
CCA
10
F
.01
F
3.3V
.01
F
V
CC
C1
33p
X1
18pF Parallel Crystal
C2
27p
XTAL_OUT
XTAL_IN