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I have this schematics and I want op amp to saturate but I am not able to finish simulation due to convergence error. I have tried add 1 ohm resistance,1p capacitance to circuit, reduce ABSTOL to 10uA, reduce RELTOL to 0.1 ohm, reduce minimal step to 100ps and change iteration metod in setting but without success. Any suggestions?

Reducing minimum delta to make the circuit converge.

ERROR(ORPSIM-15138): Convergence problem in Transient Analysis at Time =  2.710E-06.
         Time step =  186.3E-21, minimum allowable step size =  1.000E-18


These voltages failed to converge:


V(X_U1.44)                =    540.58V  \   -236.81V




These supply currents failed to converge:


I(E_MULT1)                =    13.99uA  \    13.37uA
I(X_U1.EOS)               =   253.09nA  \   250.76nA
I(X_U1.EO4)               =  -153.14pA  \  -278.53pA




These devices failed to converge:
    Q_Q1      X_U1.Q4


ERROR(ORPSIM-15659): Discontinuing simulation due to convergence problem

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andz
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1 Answers1

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The amplifier itself is definitely okay, you need to look elsewhere for the error. It starts to saturate above 90 mVp at 2MHz (30mV@1MHz). ad1

ad2

csabahu
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  • I tried only op amp but it does not work, it just saturates and then simulation crashes. – andz Sep 27 '20 at 23:51
  • Very interesting. Is the model the same as what is on the AD website? I used to have no built-in model. – csabahu Sep 28 '20 at 07:36
  • I downloaded the model from AD and it still didn't work, but when I tried only op amp it did. So I changed transistor from BC807-40 to BC817-16 and now it is working. Have no idea why. – andz Sep 28 '20 at 20:13
  • This makes it more and more interesting. I will also look at the transistors. – csabahu Sep 29 '20 at 06:04
  • It works for me with both, but both BC models come from here. – csabahu Sep 29 '20 at 06:51
  • I tried BC817-40 from your link with no success, but when I add 100 ohm resistor to multiplier output then it works with any transistor or amplifier. – andz Sep 29 '20 at 21:54
  • I see the difference, I used a [50 Ohm] (https://imgur.com/a/lUqi1EJ) internal resistance generator. Thus, the situation is similar to that of the intermediate 100 ohms. – csabahu Sep 29 '20 at 22:21
  • At last we did find out, thank you for your time. – andz Sep 30 '20 at 01:17