
ICS844002-01
FEMTOCLOCKS CRYSTAL-TO-LVDS FREQUENCY SYNTHESIZER
IDT / ICS LVDS FREQUENCY SYNTHESIZER
8
ICS844002AG-01 REV. A SEPTEMBER 28, 2007
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. The ICS844002-01 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 bypass
capacitors should be used for each pin. To achieve optimum jitter
performance, power supply isolation is required. Figure 1
illustrates how a 10
resistor along with a 10F and a 0.01F
bypass capacitor should be connected to each VDDA pin.
Figure 1. Power Supply Filtering
Recommendations for Unused Input and Output Pins
Inputs:
LVCMOS Control Pins
All control pins have internal pull-ups or pull-downs; 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
3.3V or 2.5V
10
10F
.01F