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Slew rate of an opamp

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Spliter

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What is the high level of step impulse for testing slew rate of an opamp? Unity gain topology, supply 1.8V. May I put step from 0V to 1.8V with rise edge of 1ps, or there is some way to exactly calculate levels?
 

Unity gain isn't a topology, it's a feedback configuration. Under unity gain condition -- a well designed output stage assumed -- the ICMR (Input Common Mode Range) will determine the valid input range. So for a reasonable slew rate measurement, the input steps should be confined within this ICMR.

If you inject a full supply voltage range square wave input signal, the output slew rate most probably will be worse, as the opAmp needs time to reach a working OP (operation point) each time the input signal enters into the ICMR.
 
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Hi Spliter, as you got suggestion from erikl, Unity gain is the feedback, gives close loop response in the worst case.
You also need to add output capacitor as per design, to compensate the output stage current loading and to get the correct slew rate response.
Because your OPAMP may be very fast and it becomes difficult to measure slewing in the ICMR range. Add required capacitive load to compensate this.
 

Another possible configuration might be the inverting unity gain configuration without loading effects by driving resistors with voltage controlled voltage sources.
 

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