ICS844020-45 Datasheet, PDF (8/13 Pages) Integrated Device Technology – FEMTOCLOCK™ CRYSTAL-TO-LVDS/LVCMOS FREQUENCY SYNTHESIZER

ICS844020-45
FEMTOCLOCK™ CRYSTAL-TO-LVDS/LVCMOS FREQUENCY SYNTHESIZER
APPLICATION INFORMATION
PRELIMINARY
POWER SUPPLY FILTERING TECHNIQUES
As in any high speed analog circuitry, the power supply pins
are vulnerable to random noise. The ICS844020-45 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.
2.5V
V
DD
.01µF 10Ω
V_DDA
.01µF
10µF
FIGURE 1. POWER SUPPLY FILTERING
CRYSTAL INPUT INTERFACE
The ICS844020-45 has been characterized with 18pF parallel
resonant crystals. The capacitor values shown in Figure 2 below
were determined using a 25MHz, 18pF parallel resonant crystal
and were chosen to minimize the ppm error.
X1
18pF Parallel Cry stal
XTAL_IN
C1
22p
XTAL_OUT
C2
22p
ICS84332
Figure 2. CRYSTAL INPUt INTERFACE
IDT^™ / ICS^™ LVDS/LVCMOS FREQUENCY SYNTHESIZER
8
ICS844020-45 REV A JUNE 14, 2006