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# Measure Opamp Settling Time in Opamp

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#### Anachip

##### Member level 2
Hi,

Please guide me how to measure the opamp settling time in Cadence and also tell me why we need to very concern of the opamp's settling time.

Cheers,
Anachip

Connect the op-amp to unity-gain configuration. Input a square wave signal and run transient analysis. The settling time is where your output square waveform start to rise until it settle to constant level. Settling time shows how fast your op-amp can react for a given input. For higher frequency operataion the op-amp should have fast settling time.

I think u can not put a unity-gain configuration but the real feedback netweek that u need.
Becasue the feedback factor can change the settling time.

Best Regards,
Louis

Connect the op-amp to follower configuration. Input a square wave signal (insure it is a small signal and the opa is in the linear region )and run transient analysis,plot the out wave. Pls see the picture!

huojinsi said:
Connect the op-amp to follower configuration. Input a square wave signal (insure it is a small signal and the opa is in the linear region )and run transient analysis,plot the out wave. Pls see the picture!

Hi Huojinsi,

What you mean by saying a small signal and the opa is in linear region. Do you mean that the input pulse signal need to be small swing (and not as like rail to rail in the slew rate measurement) and the linear means keep the opamp in saturation?
You always gives a good explanation with pics, that is good. Keep it up.

Anachip wrote:
What you mean by saying a small signal and the opa is in linear region. Do you mean that the input pulse signal need to be small swing (and not as like rail to rail in the slew rate measurement) and the linear means keep the opamp in saturation?

Linear means the out of opa have the same shape as the input of opa and the output transistor of opa is operating in amplify region. Pls see the transfer characteristic of opa.

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