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AFE7901: Min Full scale input power & meaning of NFMin

franziskus
Expert 7178 points
Part Number: AFE7901

Team,

What does the “Min Full scale input power, at device pins” on page 22 refer to?
Does it refer to the power at 100 ohms, i.e. approx. 0.9Vpp?
As a full-scale value, I would have expected a voltage value.
Is only the power important in this case, so would using a 1:1 balun not yield any other full-scale performance?


Which data does the NFMin of approx. 22dB specified in the data sheet refer to?
I can't fully understand the calculated value.

Best regards

  • 0
    TI__Expert 3980 points

    Hi Franziskus,

    “Min Full scale input power, at device pins” refers to the minimum input power at the device pins that will make the ADCs report a full-scale code with DSA = 0. The dBm value is proportional to a voltage value, so the voltage value and impedance is also important since P(dBm) follows the following equation:

    P(dBm) = 10*Log10((1000/Z)*(Vpp/(2√2))^2)

    The noise figure (NF) values in that section of the datasheet refer to the NF for the RX channel. This is dependent on the DSA because the input stage of the receiver chain is a programmable Digital Step Attenuator (DSA), whose goal is to extend the effective dynamic range of the RX chain by attenuating the large signals before reaching the ADC.

    By increasing the DSA you attenuate your input signal which in return increases your NF. Which is why the minimum NF would be when your DSA is set to the lowest attenuation values. This is why the NF is given for different DSA values.

    Best,

    Camilo

  • 0 in reply to Camilo Garcia Trujillo
    TI__Expert 7178 points

    Thanks Camilo! I will get back to you after talking to the customer.

  • 0 in reply to franziskus
    TI__Expert 3980 points

    Hi Franziskus,

    No problem.

    Best,

    Camilo