
IDT / ICS LVDS FREQUENCY SYNTHESIZER
8
ICS844002AG REV. B JULY 25, 2008
ICS844002
FEMTOCLOCKS CRYSTAL-TO-LVDS FREQUENCY SYNTHESIZER
APPLICATION INFORMATION
CRYSTAL INPUT INTERFACE
The ICS844002 has been characterized with 18pF parallel
resonant crystals. The capacitor values shown in
Figure 2 below
FIGURE 2. CRYSTAL INPUt INTERFACE
were determined using a 26.5625MHz, 18pF parallel resonant
crystal and were chosen to minimize the ppm error.
POWER SUPPLY FILTERING TECHNIQUES
As in any high speed analog circuitry, the power supply pins are
vulnerable to random noise. To achieve optimum jitter perfor-
mance, power supply isolation is required. The ICS844002
provides separate power supplies to isolate any high switching
noise from the outputs to the internal PLL. V
DD, VDDA and VDDO
should be individually connected to the power supply
plane through vias, and 0.01F bypass capacitors should be used
for each pin.
Figure 1 illustrates this for a generic V
CC pin and also
shows that V
DDA requires
that an additional10
Ω resistor
along with a 10F bypass capacitor be connected to the 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
XTAL_IN
XTAL_OUT
X1
18pF Parallel Crystal
C1
18pF
C2
18pF