
ICS844002I-01
FEMTOCLOCKS CRYSTAL-TO-LVDS FREQUENCY SYNTHESIZER
IDT / ICS LVDS FREQUENCY SYNTHESIZER
7
ICS844002AGI-01 REV. D OCTOBER 20, 2008
Parameter Measurement Information, continued
Differential Offset Voltage Setup
Application Information
Power Supply Filtering Technique
As in any high speed analog circuitry, the power supply pins are
vulnerable to random noise. To achieve optimum jitter perform-
ance, power supply isolation is required. The ICS844002I-01
provides separate power supplies to isolate any high switching
noise from the outputs to the internal PLL. VDD, VDDA and VDDO
should be individually connected to the power supply plane
through vias, and 0.01F bypass capacitors should be used for
each pin. Figure 1 illustrates this for a generic VDD pin and also
shows that VDDA requires that an additional 10 resistor along with
a 10
F bypass capacitor be connected to the V
DDA pin.
Figure 1. Power Supply Filtering
Recommendations for Unused Input and Output Pins
Inputs:
LVCMOS Control Pins
All control pins have internal pulldowns; additional resistance is not
required but can be added for additional protection. A 1k
resistor
can be used.
REF_CLK Input
For applications not requiring the use of the reference clock,
it can be left floating. Though not required, but for additional
protection, a 1k
resistor can be tied from the REF_CLK to
ground.
Crystal Inputs
For applications not requiring the use of the crystal oscillator input,
both XTAL_IN and XTAL_OUT can be left floating. Though not
required, but for additional protection, a 1k
resistor can be tied
from XTAL_IN to ground.
Outputs:
LVDS Outputs
All unused LVDS output pairs can be either left floating or
terminated with 100
across. If they are left floating, we
recommend that there is no trace attached.
100
out
LVDS
DC Input
VOD/ VOD
V
DD
VDD
VDDA
2.5V
10
10F
.01F