ICS844002 Datasheet, PDF (8/16 Pages) Integrated Device Technology – FEMTOCLOCKS™ CRYSTAL-TO-LVDS FREQUENCY SYNTHESIZER

ICS844002
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 ICS844002 provides sepa-
rate 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
0.01μF
bypass
capacitor
should
be
connected
to
each
V
DDA
pin.
3.3V or 2.5V
V_DD
.01μF
10Ω
V
DDA
.01μF
10μF
FIGURE 1. POWER SUPPLY FILTERING
CRYSTAL INPUT INTERFACE
The ICS844002 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
Figure 2. CRYSTAL INPUt INTERFACE
IDT^™ / ICS^™ LVDS FREQUENCY SYNTHESIZER
8
ICS844002AG REV. A SEPTEMBER 28, 2007