
843081AGI-01
www.idt.com
REV. C JULY 25, 2010
7
ICS843081I-01
FEMTOCLOCKSCRYSTAL-TO-
3.3V, 2.5V LVPECL CLOCK MULTIPLIER
APPLICATION INFORMATION
As in any high speed analog circuitry, the power supply pins
are vulnerable to random noise. The ICS843081I-01 provides
separate 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
Ω resistor along with a 10μF and a .01μF bypass
capacitor should be connected to each V
CCA pin. The 10
Ω
resistor can also be replaced by a ferrite bead.
POWER SUPPLY FILTERING TECHNIQUES
FIGURE 1. POWER SUPPLY FILTERING
10
Ω
V
CCA
10
μF
.01
μF
3.3V or 2.5V
.01
μF
V
CC
Figure 2. CRYSTAL INPUt INTERFACE
CRYSTAL INPUT INTERFACE
The ICS843081I-01 has been characterized with 18pF parallel
resonant crystals. The capacitor values, C1 and C2, shown in
Figure 2 below were determined using an 18pF parallel reso-
nant crystal and were chosen to minimize the ppm error. The
optimum C1 and C2 values can be slightly adjusted for different
board layouts.
ICS843081I-01
C1
33p
X1
18pF Parallel Crystal
C2
22p
XTAL_OUT
XTAL_IN