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Good OpAmp choice for TIA in UI panel?

Tom Schroetter
Prodigy 30 points
Other Parts Discussed in Thread: OPA320, OPA2320

Hello TI community!

 

I am looking for a good opamp (single supply) in a transimpedance amplifier application and was hoping to get some recommendations from the experienced engineers here.

We are developing a user interface panel that uses lot's of photodiodes to detect infrared light (pulsed at 40 kHz).

The photodiodes are connected through a multiplexer to the transimpedance amplifier, the signal is then passed through a bandpass filter, demodulator and finally read by a microcontroller.

At this point we are using SMD photodiodes by Everlight (PD15/21C-TR8) which produce a very small current (datasheet states 3uA but we measured up to 10uA under certain conditions).

The multiplexers are driven with up to 50 kHz frequency.

 

Can someone recommend a good part for this application?

If you need any more information for a good recommendation please let me know.

 

Thank you very much & have a great day!

Tom

  • 0
    Guru 21975 points

    Tom,

    You may want to consider the OPA320, a relatively new op amp from TI. I've made a quick simulation with a 10uA, 100kHz square wave step current at the input of a 200k-ohm TIA. The tricky issue may be minimizing the capacitance at the inverting input due to the multiplexer. I've shown 15pF including the photodiode capacitance. You will need to increase the feedback capacitor if the input C gets much larger and the response will slow down. I've shown a 2V bias on non-inverting input to reverse bias the photodiode and bias the op amp output in a linear range. This could be adjusted as needed.

    Regards, Bruce.

  • 0
    Genius 5430 points

    Tom;

    Bruce's suggestion is a good one to follow. If, however, you have problems with the multiplexing your photodiodes into a transimpedance amplifier, you might consider using a transimpedance amplifier for each photodiode and placing the multiplexer at the output of the amplifiers. To prevent any instability from the capacitance of the MUX, add a small resistor (50 ohms or so) between the amplifier output and the MUX input.

  • 0 in reply to Bruce Trump
    Prodigy 30 points

    Bruce, thank you very much for your advice, it is much appreciated!

     

    I will look into the OPA320 you recommended. It seems though that it is still in PREVIEW status?! Do you happen to know when it will be ACTIVE?

     

     

  • 0 in reply to Neil Albaugh
    Prodigy 30 points

    Neil, thank you very much for your suggestion.

    Due to the amount of photodiodes in this project it is not possible to equip every one with a separate transimpedance amplifier but we need to multiplex them before the tia.

    This will probably not give the same precision but will hopefully be enough for this application.

     

    Thank you again and have a great day!

    Tom

  • 0 in reply to Tom Schroetter
    Guru 21975 points

    Tom,

    Woops... I see now that the dual version, OPA2320 is released but the single version is not. I believe that the single version must be close to release. I will check on Monday. Samples may be available.

    Regards, Bruce.