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Design >> Analog Design >> Step responce
https://designers-guide.org/forum/YaBB.pl?num=1353081881

Message started by summi on Nov 16^th, 2012, 8:04am

Title: Step responce
Post by summi on Nov 16^th, 2012, 8:04am

Dear forum,
I would like to know why only step reponce will be evaluated to characterize a feedback system performance, why not ramp responce? I would be appriciate if any one exapin with some example, I haven't find any clue from text books in this regard.

Br,
Summi.

Title: Re: Step responce
Post by raja.cedt on Nov 16^th, 2012, 3:19pm

Hello,
Step change is fast compared to all, hence it has all frequency components, so step response fairly indicate's wideband performance. Coming to ramp response it depends on the application, for example consider PLL which works on Phase variable, so to evaluate response to a step change in frequency ramp response is necessary because phase is integral of frequency, step change in frequency is ramp change in phase. refer basic control theory books get more examples.

Thanks,
Raj.

Title: Re: Step responce
Post by buddypoor on Nov 17^th, 2012, 2:13am

There is another important function in then time domain: The impulse response.
In context with your question you should know
* that the impulse response is directly related to the transfer function using the (inverse) LAPLACE transformation, and
* that the impulse response is the derivative (slope) of the step response

Title: Re: Step responce
Post by raja.cedt on Nov 17^th, 2012, 6:13am

Hello buddy poor,
then why no one check for impulse response, i know both step and impulse response are related.

Thanks,
Raj.

Title: Re: Step responce
Post by buddypoor on Nov 17^th, 2012, 6:27am

I suppose, you know the shape of the test signal called "impulse". For practical reasons it is not a good idea to select such a test signal because you can do nothing else than to approximate it. However, simulation programs offer the possibility to check the impulse response.

Title: Re: Step responce
Post by raja.cedt on Nov 18^th, 2012, 6:35am

hello buddy poor,
yes i agree with you, impulse you can't generate but at the same you can't generate even a step. Always we give non-zero rise time whose derivative is pulse rather an impulse. So why no one use this method to find impulse response of an opamp?

Thanks,
Raj.

Title: Re: Step responce
Post by buddypoor on Nov 18^th, 2012, 6:50am

raja.cedt wrote on Nov 18^th, 2012, 6:35am:

Are you speaking about measurement or simulation? As I have mentioned - simulator programs offer the possibility of simulating the impulse response. But - why are you interested? What are the advantages?
On the other hand - the mentioned step response restrictions (finite rise time) are negligible.
If you want you can select pico-sec rise times.