
IDT / ICS FEMTOCLOCKS CLOCK GENERATOR
7
ICS844001 REV A NOVEMBER 2, 2012
ICS844001
FEMTOCLOCKS CRYSTAL-TO-LVDS CLOCK GENERATOR
APPLICATION INFORMATION
Figure 2. CRYSTAL INPUt INTERFACE
CRYSTAL INPUT INTERFACE
The ICS844001 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
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.
C1
33p
X1
18pF Parallel Crystal
C2
27p
XTAL_OUT
XTAL_IN
POWER SUPPLY FILTERING TECHNIQUES
As in any high speed analog circuitry, the power supply pins
are vulnerable to random noise. The ICS844001 provides sepa-
rate power supplies to isolate any high switching
noise from the outputs to the internal PLL. V
DD and VDDA 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 connected to
each V
DDA pin.
FIGURE 1. POWER SUPPLY FILTERING
10
Ω
V
DDA
10
μF
.01
μF
3.3V or 2.5V
.01
μF
V
DD