ICS844256 Datasheet, PDF (9/13 Pages) Integrated Circuit Systems – FEMTOCLOCKS™ CRYSTAL-TO-LVDS FREQUENCY SYNTHESIZER W/INTEGRATED FANOUT BUFFER

Integrated
Circuit
Systems, Inc.
PRELIMINARY
ICS844256
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 ICS844256 pro-
vides separate power supplies to isolate any high switch-
ing 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 ICS844256 has been characterized with 18pF parallel
resonant crystals. The capacitor values shown in Figure 2
below were determined using an 18pF parallel resonant crys-
tal 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
844256AM
www.icst.com/products/hiperclocks.html
9
REV. A NOVEMBER 29, 2005