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AM26LV31E: Is it suitable for converting photodiode single-ended signal into differential signal?

Ven Hsu
Prodigy 30 points
Part Number: AM26LV31E
Other Parts Discussed in Thread: AFE4400,

Tool/software:

Since our photodiode is in a single-ended input configuration, would the AM26LV31E be suitable for converting the photodiode into a differential signal to serve as the input of the AFE4400? Thank you.

  • 0
    Guru 295240 points

    No, it has digital inputs that expect valid logic voltage levels.

    You should use photodiodes that can be floating.

  • 0
    TI__Genius 15321 points

    Hi Ven,

    Thank you for your question. The AFE is looking for an analog input to the device. I am not an expert on the AFE4400, but I believe that you would want to use a balun to convert a single-ended to differential signal. Mini Circuits has several options to choose from, depending on your input frequency: RF Transformers and Baluns (minicircuits.com)

    The main thing to consider here is the input full-scale range of the device. Because the TIA has a full-scale range of ±1 V, TI recommends that the input to the ADC does not exceed ±1 V, which is approximately 80% of its full-scale (datasheet pg. 74)

    I have also drawn you a diagram for this situation. It is helpful to understand this diagram along with the diagram in the AFE4400 datasheet on pg. 72. Notice that the AFE4400 datasheet mentions a Vcm = 0.9 V (datasheet pg. 9, “Common-mode voltage on input pins”). This means that the differential signal IN+ / IN- will swing around 0.9V. I understand the ±1 V to be a maximum swing of 2 Vpp, so each differential leg has an allowable swing of 1 Vpp. Here is another helpful reference to understand this: (+) [FAQ] ADS5263: Differential input voltage swing vs single-ended signal pk-pk voltage.

    I also found this to be a helpful resource (question 11): (+) AFE4400 / AFE4490 / AFE4403 / AFE4404 FAQs

    Regards, Amy