ICS843256 Datasheet, PDF (8/13 Pages) Integrated Circuit Systems – FEMTOCLOCKS™ CRYSTAL-TO-3.3V LVPECL FREQUENCY SYNTHESIZER W/INTEGRATED FANOUT BUFFER

Integrated
Circuit
Systems, Inc.
PRELIMINARY
ICS843256
FEMTOCLOCKS™ CRYSTAL-TO-3.3V LVPECL
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 ICS843256 provides sepa-
rate power supplies to isolate any high switching
noise from the outputs to the internal PLL. V_CC, V_CCA and V_CCO
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 iso-
lation is required. Figure 1 illustrates how a 10Ω resistor along
with a 10μF and a .01μF bypass capacitor should be con-
nected to each V_CCA pin. The 10Ω resistor can also be re-
placed by a ferrite bead.
V_CC
V
CCA
3.3V
.01μF 10Ω
.01μF
10μF
FIGURE 1. POWER SUPPLY FILTERING
CRYSTAL INPUT INTERFACE
The ICS843256 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_IN
C1
18p
XTAL_OUT
C2
22p
Figure 2. CRYSTAL INPUt INTERFACE
843256AM
www.icst.com/products/hiperclocks.html
8
REV. A NOVEMBER 29, 2005