ICS844004I Datasheet, PDF (8/12 Pages) Integrated Circuit Systems – FEMTOCLOCKS™ CRYSTAL-TO-LVDS FREQUENCY SYNTHESIZER

Integrated
Circuit
Systems, Inc.
PRELIMINARY
ICS844004I
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 ICS844004I provides
separate power supplies to isolate any high switching
noise from the outputs to the internal PLL. V_DD, V_DDA, and V_DDO
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.
3.3V or 2.5V
V
DD
.01μF 10 Ω
V
DDA
.01μF
10μF
FIGURE 1. POWER SUPPLY FILTERING
CRYSTAL INPUT INTERFACE
The ICS844004I has been characterized with 18pF parallel
resonant crystals. The capacitor values shown in Figure 2
below were determined using a 26.5625MHz 18pF parallel
resonant crystal and were chosen to minimize the ppm error.
X1
18pF Parallel Crystal
XTAL_OUT
C1
33p
XTAL_IN
C2
27p
ICS844004I
Figure 2. CRYSTAL INPUt INTERFACE
844004AGI
www.icst.com/products/hiperclocks.html
8
REV. A JUNE 15, 2005