Hi all,
I'm trying to build a circuit that can help an op amp to recover from saturation.
After some online search, I found few clipping circuits where it limits output of an op amp but does nothing to keep a difference between two input terminals of an op amp to a reasonable range.
So I tried building circuit which clips an output voltage AND keeps Vneg and Vpos virtually shorted.
My rationales were
1. If the input voltage reaches 2.8V, output will be at -2.8V and D29~D32 will start to conduct (assuming Vf=0.7V). Output will remain at around -2.8V and Vneg will be around 0V.
2. For Vin=-2.8V, D25~D28 will conduct and Vout=2.8V and Vneg=0V.
3. Since Vneg is kept close to 0V even when the circuit is over-driven, the op amp will recover quickly.
The simulation result shows that the output is well clipped at around -3V (35ns to 80ns) and Vneg is about 0V. But from 80ns to 120ns, it seems the op amp is losing control of Vout. I was expecting Vout to remain at -3V until around 110ns.
Can anyone tell me why the op amp is behaving weirdly? Is the design fundamentally wrong and won't work?
P.S The application of this circuit specifically requires 1MOhm input resistance and X1 gain. So I don't have a choice but to use 1MOhm Rf.
I'm trying to build a circuit that can help an op amp to recover from saturation.
After some online search, I found few clipping circuits where it limits output of an op amp but does nothing to keep a difference between two input terminals of an op amp to a reasonable range.
So I tried building circuit which clips an output voltage AND keeps Vneg and Vpos virtually shorted.
My rationales were
1. If the input voltage reaches 2.8V, output will be at -2.8V and D29~D32 will start to conduct (assuming Vf=0.7V). Output will remain at around -2.8V and Vneg will be around 0V.
2. For Vin=-2.8V, D25~D28 will conduct and Vout=2.8V and Vneg=0V.
3. Since Vneg is kept close to 0V even when the circuit is over-driven, the op amp will recover quickly.
The simulation result shows that the output is well clipped at around -3V (35ns to 80ns) and Vneg is about 0V. But from 80ns to 120ns, it seems the op amp is losing control of Vout. I was expecting Vout to remain at -3V until around 110ns.
Can anyone tell me why the op amp is behaving weirdly? Is the design fundamentally wrong and won't work?
P.S The application of this circuit specifically requires 1MOhm input resistance and X1 gain. So I don't have a choice but to use 1MOhm Rf.
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