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ADF4355 REFIN configuration

Question asked by sss on Feb 25, 2016
Latest reply on Feb 26, 2016 by sss

Hi all,

 

Our customor will start to evaluate the ADF4355 EVB.

In the datasheet,

"When the input reference frequency is below 250 MHz, it is recommended to operate in single-ended mode for best spur performance. "

"For optimum integer boundary spur performance, use the single-ended setting for all references up to 250 MHz (even if using a differential reference signal). Use the differential setting for reference frequencies above 250 MHz."

 

Please let me know if my understanding is correct about following,

 

1.REFIN below 250 MHz @ ADF4355,

To Use the single-ended signal:

REFINA:ac-coupling recommended with internal bias

REFINB:1000pF to AGND (need the termination ?)

Reference Mode:Single-Ended Mode

 

To Use the differential signal:

REFINA:ac-coupling recommended with internal bias

REFINB:ac-coupling recommended with internal bias

Reference Mode:Single-Ended Mode

 

2.REFIN above 250 MHz @ ADF4355,

To Use the single-ended signal:

REFINA:ac-coupling recommended with internal bias

REFINB:1000pF to AGND (need the termination ?)

Reference Mode:Differential Mode

 

To Use the differential signal:

REFINA:ac-coupling recommended with internal bias

REFINB:ac-coupling recommended with internal bias

Reference Mode:Differential Mode

 

3.Why is the double ac-coupling cap ?

In the datasheet, Figure 44 and 45, ac-coupling REFIN is 1nF + 1nF.

Is it typo?

 

 

Best regards,

sss

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