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Question regarding slew rate and settling

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kidmanbasha

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I understand that when a large step input is applied to the op amp this causes

slewing because the diff amp's input transistors are in cut off/triode. As you can see

that the output after slewing starts to ripple. During this rippling the transistors are in

saturation and the error voltage Ve is decreasing due to the -ve feedback. I want to

know if this rippling would take place if there wasn't any feedback or not. In other

words, if there wasn't feedback, what would make the transistors go into saturation

and thus have rippling?
 

kidmanbasha said:
I understand that when a large step input is applied to the op amp this causes slewing because the diff amp's input transistors are in cut off/triode. As you can see that the output after slewing starts to ripple. During this rippling the transistors are in saturation and the error voltage Ve is decreasing due to the -ve feedback. I want to know if this rippling would take place if there wasn't any feedback or not. In other words, if there wasn't feedback, what would make the transistors go into saturation
and thus have rippling?
Click to expand...

As in each feedback system the rippling is an indication that the loop gain has a marginal phase margin (loop gain implies that there is feedback !).
With other words - rippling is an indication for complex poles (pole Q>0.5).
As the opamp alone (without feedback) has only real poles, such a rippling can occur only for an opamp in a closed feedback loop configuration.
 
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