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Re: Clock limitations on AD9528 not clear

I have a further question which is related to this matter.

I am using ADIsimCLK v1.70 to verify my proposed set-up for the AD9528.

I end up having a frequency of 1.28906GHz at the output of M1 (VCO freq 3.86719GHz, M1 = 3 (some small rounding errors)) which results in the error "Max M1 out freq is 1.25GHz". I cannot find an explicit reference to this limitation in the datasheet.

I plan to divide this down using the 8-bit channel dividers in the clock distribution part to be less than 1GHz at each output.

Is this an error in ADIsimCLK?

Should the limitation be placed after the channel divider (as per your reply)?

Is there a maximum frequency that the 8-bit channel dividers can be run at?

I have just noticed that this is actually explained here (Query in AD9371 Evaluation Board  VCXO selection doc ).

I assume this is just a bug in ADIsimCLK. Can you please confirm?

  • Datasheet says max frequency as 1.25 GHz, and hence it is limited in SimCLk as well.

     Moving to clock and timing subspace for more comments.

  • The datasheet says the max frequency of the output of the device is limited to 1.25 GHz for two of the output channels.

    It makes no reference as to the max frequency at the output of M1 (before the 8-bit output divider) whereas SimCLK does.

    Which is correct - the datasheet or SimCLK?

  • Actually, the resonse you posted here Clock limitations on AD9528 not clear  


    Looks like it is a bug in ADIsimCLK. Moving it to clock and timing subspace for further comments.


    It should not be  M1 frequency as the dividers are after that. What is referred as limitation is output of AD9528. (Output 1 and Output 2 with a maximum frequency of 1.25 GHz, and 12 outputs up to 1 GHz )



    looks like you answer my question.


    Copying here so that this topic is complete.

  • In Simclk the 8 bit divider is given in the clock distribution configuration , configure tab.

  • Yes. Even when all of the 8 bit dividers are configured to output low frequencies, simCLK reports that "Max M1 out freq is 1.25GHz".

    This resolves to 2 questions which are not specified in the datasheet.

    What is the maximum frequency that the 8-bit Output dividers can be run at?

    What is the maximum output frequency of the M1 divider?

  • Hi liamm,

    The 2 dividers you are talking about actually have different frequency ranges on them.

    The M1 divider can operate at a higher rate than 1.25GHz.

    However, the output channels can only operate up to 1.25GHz.

    The documentation is not clear, especially since we have multiple areas that seem to contradict each other, datasheet, evaluation software, ADISimclk. We can add a section in the datasheet regarding this, as this has come up more than once.



  • Hello Steve,

    Thanks for the clarification. I realise my earlier question was slighlty ambiguous.

    I was trying to clarify the maximum input frequency to the 8-bit output divider.

    I understand that the output of the 8-bit divider is limited to 1.25GHz / 1GHz.

    An updated datasheet would be appreciated.