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Original question:

AFE7950EVM: Is it possible to dynamically change the NCO frequency?

AFE8000: NCO Dynamic update limitation: within same nyquist only

Deva Guru
Prodigy 225 points
Part Number: AFE8000

Tool/software:

Hi,

i went through the query in below link,

https://e2e.ti.com/support/rf-microwave-group/rf-microwave/f/rf-microwave-forum/1279331/afe7950evm-is-it-possible-to-dynamically-change-the-nco-frequency/4857586#4857586

With AFE79xx series, NCO frequency can be dynamically changed within the same Nyquist zone only. (eg: If sampling freq is 3GHz and NCO1 is set to 1.3GHz then it is possible change dynamically only within the same nyquist i.e, 0.75 to 1.5GHz and cannot be set to other nyquist i.e,350MHz).

Does the same limitation apply to AFE8000 ?

  • +1
    TI__Genius 10865 points

    Hi Deva Guru,

    Yes. The same limitation applies to AFE8000 as well. Nyquist zone cannot be changed dynamically. 

    Deva Guru said:
    If sampling freq is 3GHz and NCO1 is set to 1.3GHz then it is possible change dynamically only within the same nyquist i.e, 0.75 to 1.5GHz and cannot be set to other nyquist i.e,350MHz

    Please note that Nyquist zones have width of 0.5 times of the sample rate. For 3GHz sampling rate, first Nyquist zone is from DC-1.5GHz. Second Nyquist is from 1.5 to 3GHz. In the example you mentioned, 1.3GHz and 350 MHz are in first Nyquist zone only. 

    Regards,

    Vijay