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Transconductance Op Amp

Clive Bolton
Prodigy 20 points

Other Parts Discussed in Thread: OPA602, TINA-TI

I'm redoing an old design and need to replace an OPA602 op amp in a transconductance amplifier. I'm using the exact same circuit as in the original design, but with the different op amp. The design pulses in and out of oscillation. The oscillation is there without the photodiode attached but gets more exagerated when the photodiode is plugged in.

I've checked the layout and power, and everything looks grand. I've tried to squelch the oscillation by adding a cap directly across the output and (-), tried adding an additional cap across the photodiode. I've tried reducing the feedback resistor.

Yes, there are probably things that could be done to make this circuit better, but the old design has worked fine for 10+ years and so I can't justify getting creative here!

Thank you in advance

7713.transconductance op amp.pdf

  • 0
    Genius 5430 points

    Clive;

    You have a transimpedance amplifier (current in, voltage out) not a transconductance amplifier (voltage in, current out).

    I think you will find the answer to your problem by simulating  simple version of your circuit (only Rf, Cf, op amp, & photodiode) in TINA-TI. Then add the other components to see their effect.