ICS844S42I Datasheet, PDF(15/27 Page) Integrated Device Technology – On-chip crystal oscillator for reference frequency generation

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ICS844S42I Datasheet, PDF (15/27 Pages) Integrated Device Technology – On-chip crystal oscillator for reference frequency generation

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ICS844S42I Data Sheet

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 performance,

power supply isolation is required. The ICS844S42I provides

separate power supplies to isolate any high switching noise from the

outputs to the internal PLL. VDD, VDDA, VDDOA and VDDOB should be

individually connected to the power supply plane through vias, and

0.01ÂµF 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 10ï resistor along with a 10ïF bypass

capacitor be connected to the VDDA pin.

DUAL OUTPUT RF FREQUENCY SYNTHESIZER

3.3V

VDD

.01ÂµF 10Î©

VDDA

.01ÂµF

10ÂµF

Figure 1. Power Supply Filtering

Recommendations for Unused Input and Output Pins

Inputs:

LVCMOS Control Pins

All control pins have internal pullups or pulldowns; additional

resistance is not required but can be added for additional protection.

A 1kï resistor can be used.

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 1kï resistor can be tied from

XTAL_IN to ground.

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 1kï

resistor can be tied from the REF_CLK to ground.

Outputs:

LVPECL Outputs

All unused LVPECL outputs can be left floating. We recommend that

there is no trace attached. Both sides of the differential output pair

should either be left floating or terminated.

LVDS Outputs

All unused LVDS output pairs can be either left floating or terminated

with 100ï across. If they are left floating, we recommend that there

is no trace attached.

ICS844S42BKI REVISION A FEBRUARY 21, 2012

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