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Original question:

ADS54J42: NYQUIST ZONE & CTRL NYQUIST Register setting

ADS54J42: CTRL NYQUIST & NYQUIST ZONE setting

Hiroshi Katsunaga
Mastermind 6480 points
Part Number: ADS54J42
Other Parts Discussed in Thread: ADS54J60, ADC32RF45

Hello,

My customer has a question about ADS54J42.

[Background]

This question is related with a following thread.

https://e2e.ti.com/support/data-converters/f/73/t/807324?tisearch=e2e-sitesearch&keymatch=ads54j42

They set the registers with 2021.ADS54J60_LMF_8224_2NQ.cfg in that thread.

Their configuration is as follows.

* Fs = 500MHz

* Input Frequency = 377MHz, LTE FDD 5MHz

Their test resust is as follows.

The part indicated by the circle is the spectrum that is not expected.

This is removed with CTRL NYQUIST = 0.

[Q]

Is there an appropriate order for "CTRL NYQUIST" and "NYQUIST ZONE" settings ?

You are instructed to set "NQ ZONE EN" before "NYQUIST ZONE" in ADC32RF45 D/S.

Do you know what the cause is ?

Please tell me the appropriate workaround.

Best Regards,

Hiroshi Katsunaga

  • 0
    TI__Genius 12780 points

    Hi Hiroshi,

    One of our device experts is looking into your questions, and will be back with you soon.

    Best Regards,

    Dan

  • 0 in reply to dBrock
    Mastermind 6480 points

    Hi Dan,

    This is an update.

    This phenomenon does not seem to depend on the settings of "CTRL NYQUIST" and "NYQUIST ZONE".

    I calculated the desire frequency and undesire frequency with Fs/2-Fin.

    I show it below.

    * Input Frequency = 376MHz, BW=5MHz

    * Sampling Frequency = 500MHz

    I think the unexpected spectrum is "Fs / 2-Fin Spur" in the condition where the modulated Fin straddles Fs / 4.

    A similar phenomenon occurs even when Fin = 374MHz, BW=5MHz.

    The issue is that under certain conditions it can get bigger (about 40dBc).

    They need to solve this issue as soon as possible.

    Please confirm this issue and please tell me the workaround ASAP.

    Best Regards,

    Hiroshi Katsunaga

  • 0 in reply to Hiroshi Katsunaga
    TI__Guru* 91947 points

    Hiroshi,

    The writing to "CTRL NYQUIST" and "NYQUIST ZONE" has no special order other than after all of the addresses are written to page 0x6800, the user must toggle the reset pin on address 0x00 of this page. See attached file used by the EVM GUI that shows this.

    Regarding the other issue, when I ran their settings on our frequency planner tool (see attached), it appears HD2 and HD3 fall into this BW of interest along with the HD3 image. Can they use a different sampling rate or IF frequency?

    Regards,

    Jim

    ADS54J42_LMF_8224_2NQ.cfg

    FreqPlanner-DDC-Filter Tool.xlsx

  • 0 in reply to jim s
    Mastermind 6480 points

    Hi Jim,

    Thank you for your many supports.

    I will close this thread.

    Instead, I would like to continue resolving this issue with an email.

    I sent you email.

    Please confirm it.

    Thanks and Regards,

    Hiroshi Katsunaga