ICS844246 Datasheet, PDF (9/13 Pages) Integrated Circuit Systems – FEMTOCLOCKS™ CRYSTAL-TO-LVDS FREQUENCY SYNTHESIZER W/INTEGRATED FANOUT BUFFER

Integrated
Circuit
Systems, Inc.
PRELIMINARY
ICS844246
FEMTOCLOCKS™ CRYSTAL-TO-LVDS
FREQUENCY SYNTHESIZER W/INTEGRATED FANOUT BUFFER
APPLICATION INFORMATION
POWER SUPPLY FILTERING TECHNIQUES
As in any high speed analog circuitry, the power supply pins
are vulnerable to random noise. The ICS844246 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 pin. The 10Ω resistor
can also be replaced by a ferrite bead.
V_DD
V
DDA
3.3V
.01μF 10Ω
.01μF
10μF
FIGURE 1. POWER SUPPLY FILTERING
CRYSTAL INPUT INTERFACE
The ICS844246 has been characterized with 18pF parallel
resonant crystals. The capacitor values shown in Figure 2
below were determined using an 18pF parallel resonant
crystal and were chosen to minimize the ppm error.
X1
18pF Parallel Crystal
XTAL_OUT
C1
22p
XTAL_IN
C2
22p
Figure 2. CRYSTAL INPUt INTERFACE
844246AM
www.icst.com/products/hiperclocks.html
8
REV. A SEPTEMBER 29, 2005