
843011AG
www.idt.com
REV. B JULY 26, 2010
6
ICS843011
FEMTOCLOCKSCRYSTAL-TO-
3.3V LVPECL CLOCK GENERATOR
APPLICATION INFORMATION
Figure 2. CRYSTAL INPUt INTERFACE
CRYSTAL INPUT INTERFACE
The ICS843011 has been characterized with 18pF parallel
resonant crystals. The capacitor values, C1 and C2, shown in
Figure 2 below were determined using a 26.5625MHz, 18pF par-
allel resonant crystal and were chosen to minimize the ppm er-
ror. 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 ICS843011 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.
POWER SUPPLY FILTERING TECHNIQUES
FIGURE 1. POWER SUPPLY FILTERING
10
Ω
V
CCA
10
μF
.01
μF
3.3V
.01
μF
V
CC
C1
33p
X1
18pF Parallel Crystal
C2
22p
XTAL_OUT
XTAL_IN