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Using THS3202 as a TIA

Emre Beşkazak
Prodigy 10 points
Other Parts Discussed in Thread: OPA381, THS3202, OPA657

Hi,

I want to build a receiver with a photodiode. First I set up a circiut with OPA381 and I used 10K ohm feedback resistor. It worked well with its gain of 10K. But then I wanted a faster one and decided to use THS3202. I tried to amplify in two stages. First one as TIA had an Rf of 500ohm and second as non-inverting amp had an Rf of 500ohm and 26ohm to GND. So it had a gain of 500x20=10K. But I did not get a meaningful output. What should I do? Do I need a different op-amp? 

Thanks,

Emre

  • 0
    TI__Genius 12631 points
    Hello,
    Are you using the THS3202 as a transimpedance amplifier or as the post gain amplifier? If so then that is not recommended because :
    1. The THS3202 is a current feedback amplifier and has a different compensating scheme compared to traditional voltage feedback amplifiers.
    2. The THS3202 has a large input bias current (and bias current noise) and you could run into issues because of excess noise or voltage drop due to Ibias*Rfeedback effects.
    3. The THS3202 is Not Recommended for New Designs (NRND) and so long-term supply of this product may not be guaranteed.

    For large feedback resistances a JFET input amplifier like the OPA657 is recommended. Can you please let me know:
    1. How much transimpedance gain you need?
    2. What is the capacitance of your photodiode?
    3. How much closed loop transimpedance BW is needed for your application?
    -Samir