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ADRV9002 Using the IF offset NCO in wideband

Hello

The ADRV9002 RX signal chain includes a DDC with a mixer and NCO that can be used to tune the desired bandwidth to an offset from the LO frequency. I have seen this working with the TES software at a 48kHz sample rate - I can tune an offset frequency so that the LO center spur/notch filter is no longer in-band, as well as the image spur. This is a very nice feature.

In the ADRV9001 user guide, it mentions that this functionality is for NB (<1MHz bandwidth) applications where the requirements are more stringent than WB applications. It also says that the frequency offset can be tuned up to 21MHz off from the LO.

We typically have WB applications (full 40MHz bandwidth). For us, the notch filter in the center of the band is a problem. Also, the image spur is often what limits the performance. If the NCO supports up to a 21MHz offset, this should theoretically be enough to shift the LO center spur/notch filter out of our 40MHz band of interest. I have tried to do this in TES but it didn't work. 

Does the ADRV9002 support shifting the desired band when running in a WB application? Is it just a case that it is not supported in TES yet? Or is there some other limitation which prevents this functionality from being used in WB applications (>1MHz bandwidth)?

Thank you.

  • Hello gavint,

    I do apologise for the very long delay before getting a response to your question! We're still catching up from the activity over the Christmas break.

    The User Guide does seem to suggest that your application can be supported, however I am seeing the same behavior in TES. I am not being allowed to program an NCO frequency > 1.075MHz, which I do not understand. I will go and speak to our Apps team and the SW team and try to uncover the truth of this matter.

    Again, I do apologise for the delay! I will be back shortly.

    Best Regards,
    Oisín.

  • Hello again gavint,

    After reading into this issue more, I believe I have discovered the limitation you are running into. The offset IF plus ½ of the RF signal BW should always be smaller than 20Mhz to make sure the input signal won’t be hurt by the digital filters after ADC. This means that for your application the NCO cannot be set wider that 1.075MHz in order to meet this physical limitations of the device.
    Best Regards,
    Oisín.
  • Hello Oisin

    Thank you for replying.

    So if I were to choose a 20MHz bandwidth with an IF offset of 10MHz, that should then work. Is that correct? Because the limitation of offset IF + 1/2 of RF signal BW will be less than 20MHz.

    If this does work then that will still be a useful feature at a fairly wide bandwidth.

    Thanks

    Gavin

  • Hi Gavin,

    I can confirm that a 20MHz BW with IF of 10MHz does seem to be allowed by our SW, so you should be okay to test that configuration out for yourself.

    Best Regards,
    Oisín.