• State Resolved
  • Locked Locked
  • Replies 8 replies
  • Subscribers 46 subscribers
  • Views 275 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

ADC3221: What does special mode do?

Yuan Dao
Prodigy 110 points
Part Number: ADC3221

Datasheet mentions a "special mode" for best performance. What does this special mode do, and what performance does it improve?

And what is "High IF mode"? My sampling rate is lower than 25 MHz, and my input signal is lower than 10 MHz, for best performance, should I disable "High IF mode" by setting all the related registers to 0?

Thank you.

  • +1
    TI__Genius 15321 points

    Hi Yuan,

    The special modes are for SNR improvement. You can test the improvement factor in your use case by setting / unsetting this register, but we recommend setting the default write to 1 for optimal performance. 

    Additionally, High IF mode would improve HD3 for frequencies above 100MHz - but since you are sampling a 10MHz signal, there is no need to set this register - just set bit 1 to 0 for normal operation.

    Regards, Amy

  • 0 in reply to Amy
    Prodigy 110 points

    Forgot to mention, I tried setting / unsetting these registers (439h, 539h), and there's no observable difference in signal, noise, and spurious.

    Thank you.

  • 0 in reply to Yuan Dao
    TI__Genius 15321 points

    Hi Yuan,

    I will check with our design team to get their thoughts on the conditions that would provide a notable improvement by setting this register. I will get back to you early next week. 

    Thanks, Amy

  • 0 in reply to Amy
    TI__Genius 15321 points

    In the meantime - can you send us a screenshot of the performance you are seeing in HSDC Pro?

    Thanks, Amy

  • +1 in reply to Amy
    TI__Genius 15321 points

    Hi Yuan,

    The design team let me know that the special register needs to be set to 1 for basic functionality. If it is set to 1 in the presence of dither, it would grade performance greatly. 

    Regards, Amy

  • 0 in reply to Amy
    Prodigy 110 points

    Following picture shows the clean condition where no input signal to CH2. Noise floor about -110 dBm.

    ADC register use default configuration after reset:

    Channel 2 inputs 3 MHz, 1 Vpp sine-wave:

    Write special mode register 439h & 539h bit3 to 1:

    Recapture Channel 2's spectrum:

    Seems like not much difference.

  • +1 in reply to Yuan Dao
    TI__Genius 15321 points

    Hi Yuan,

    I can't tell from the captures, but did you turn the dither and chopper functions off in the GUI as well? According to the design team, if dither is enabled, the performance will degrade. Additionally, are you filtering the input tone? The drive level is low, the input signal is not being driven to full scale (full scale would drive the tone to -1 dBFS). Try filtering the input signal and the clocking signal to ensure you get optimal performance. Also make sure you are using quality signal sources. 

    Regards, Amy

  • 0 in reply to Amy
    Prodigy 110 points

    Dither and chopper were on by default setting, I didn't configure them. 

    I am not filtering the input or clock; it comes straight from the sig-gen.