ICS844003I Datasheet, PDF (9/13 Pages) Integrated Circuit Systems – FEMTOCLOCKS™ CRYSTAL-TO-LVDS FREQUENCY SYNTHESIZER

Integrated
Circuit
Systems, Inc.
PRELIMINARY
ICS844003I
FEMTOCLOCKS™ CRYSTAL-TO-LVDS
FREQUENCY SYNTHESIZER
APPLICATION INFORMATION
POWER SUPPLY FILTERING TECHNIQUES
As in any high speed analog circuitry, the power supply pins
are vulnerable to random noise. The ICS844003I provides
separate power supplies to isolate any high switching
noise from the outputs to the internal PLL. V_DD, V_DDA, and V_DDOx
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 2 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.
V
DD
V
DDA
3.3V
.01μF 10 Ω
.01μF
10μF
FIGURE 2. POWER SUPPLY FILTERING
CRYSTAL INPUT INTERFACE
The ICS844003I has been characterized with 18pF parallel
resonant crystals. The capacitor values shown in Figure 3 below
were determined using a 31.25MHz or 26.041666MHz 18pF paral-
lel resonant crystal and were chosen to minimize the ppm error.
X1
18pF Parallel Crystal
XTAL_OUT
C1
22p
XTAL_IN
C2
22p
ICS844003I
Figure 3. CRYSTAL INPUt INTERFACE
844003AGI
www.icst.com/products/hiperclocks.html
9
REV. B AUGUST 25, 2005