ICS844801I-24 Datasheet, PDF (7/13 Pages) Integrated Device Technology – FEMTOCLOCKS™ CRYSTAL-TO-LVDS 400MHZ FREQUENCY SYNTHESIZER

ICS844801I-24
FEMTOCLOCKS™ CRYSTAL-TO-LVDS 400MHZ FREQUENCY SYNTHESIZER
APPLICATION INFORMATION
PRELIMINARY
POWER SUPPLY FILTERING TECHNIQUES
As in any high speed analog circuitry, the power supply pins
are vulnerable to random noise. The ICS844801I-24
provides separate power supplies to isolate any high switch-
ing noise from the outputs to the internal PLL. V_DD and V_DDA
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 10Ω
resistor along with a 10µF and a .01µF bypass capacitor
should be connected to each V_DDA pin. The 10Ω resistor can
also be replaced by a ferrite bead.
3.3V or 2.5V
V
DD
.01µF
10Ω
V_DDA
.01µF
10µF
FIGURE 1. POWER SUPPLY FILTERING
CRYSTAL INPUT INTERFACE
The ICS844801I-24 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.
X1
18pF Parallel Cry stal
XTAL_IN
C1
22p
XTAL_OUT
C2
22p
ICS84332
Figure 2. CRYSTAL INPUt INTERFACE
IDT^™ / ICS^™ LVDS 400MHZ FREQUENCY SYNTHESIZER
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ICS844801AGI-24 REV A JANUARY 16, 2008