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AFE7950EVM: AFE7950...SFDR/Dynamic Range Query

Muhammad Umer
Prodigy 120 points
Part Number: AFE7950EVM
Other Parts Discussed in Thread: AFE7950

Tool/software:

Hi David,

According to the datasheet for the AFE7950, the maximum amplitude (power) that the AFE7950 device can tolerate is approximately 0 dBm at frequencies around 5 GHz, with an SFDR of approximately 78.5 dBc.

These parameters suggest that the total detectable dynamic range is around (+0 dBm to -78.5 dBm). This means that we should be able to detect signals and their frequencies within this range. Is this interpretation correct, or is there something I might have missed in these parameters?

I have also recorded some results on the AFE7950 EVM board, ranging from -2 dBm to approximately -55 dBm. The results obtained are as follows:

  • ADC counts at -2 dBm: approximately ±11,800 counts
  • ADC counts at -55 dBm: approximately ±30 counts

Given that our ADC has a 14-bit resolution and we achieve 16-bit resolution after DDC, is it possible to enhance the signal amplitude further beyond 0 dBm? This enhancement would allow the ADC counts to approach ±32,768.

Should my understanding is correct?

For Reference, I have attached some snapshots from the datasheet

  • 0
    TI__Expert 4370 points

    Hi Muhammad,

    The detectable dynamic range is mainly dependent on if you can differentiate your signal from your noise floor and any spurs around it. Therefore, it is very application specific as you can lower your noise floor using different methods such as taking more samples or increasing the decimation factor.

    Increasing the number of bits does not increase the full-scale value of the ADC. If your goal is to increase your dynamic range by measuring a signal above full scale, you could employ things like the Digital Step Attenuators (DSA) that are part of the AFE’s channels. In the case of a receive channel, the DSA will attenuate the incoming signal by a known amount, therefore letting you detect signals higher than the full scale. There is one limitation to this and it is that you can not go over the reliability limit at the device pins. These are listed in the “RF ADC Electrical Characteristics" table, there you will be able to see the limit around 5GHz.

    Best,

    Camilo

  • 0 in reply to Camilo Garcia Trujillo
    Prodigy 120 points

    Hi, Camilo

    Thanks for your answer

    Best Regards

    Muhammad Umer

  • 0 in reply to Muhammad Umer
    TI__Expert 4370 points

    Hi Muhammad,

    No problem.

    Best,

    Camilo