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ADRF6720-27 Local Frequency deviation

Question asked by PieroS. on Oct 18, 2017
Latest reply on Oct 20, 2017 by PieroS.

Dear All,

I have have an ADRF6720-27-EVALZ board and I have a problem to set correctly a local frequecy.

I use this board with a very accurate clock source at 28.6MHz (I had verified this frequency with the spectrum analyzer) and I use the internal PLL+VCO to supply che correct working frequency to the ADRF6720.

The problem is the LO_OUT signal that I measure, have a different frequency.

As you can see on the PDF attached, I try with 3 different frequencys and I found always a deviation of any kHz from the value expected:

        expected:   360MHz  ->  real the ouput: 357.41MHz

        expected:   600MHz  ->  real the ouput: 597.01MHz

        expected: 1000MHz  ->  real the ouput: 993.81MHz

For the first 2 case the deviation is about 3MHz and for the lasts is about a 2x3MHz(I think is double because one of 'div2' check at the end of VCO is disabled).

I have the same problem with my custm board.

Why there is this deviation? Any suggestion?

Regards

Piero

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