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Transfer function from a frequency response graph

Asked by Rodrigo Trigona on 14 Aug 2012
Latest activity Edited by Arkadiy Turevskiy on 19 Dec 2018
I want to know if exist some MATLAB function that can give me a transfer function by analysis from points of a frequency response graph

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2 Answers

Answer by Arkadiy Turevskiy on 22 Aug 2012
Edited by Arkadiy Turevskiy on 19 Dec 2018

System Identification Toolbox is an add-on to MATLAB for estimating transfer functions as well as other model types from time or frequency domain data.
You can estimate a transfer function from frequency domain data using the function tfest from this toolbox.
Here is a demo that might be helpful. The demo is using ssest for estimating state-space models, but you can definitely use tfest instead for estimating a transfer function.
HTH.
Arkadiy

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Thank you for your helpful answer, suggesting functions from the System Identification Toolbox. I was unaware of such a toolbox and appropriate functions for accomplishing this task. CJL

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Answer by Azzi Abdelmalek
on 14 Aug 2012

i suggest:
  1. from your frequency response, calculate a temporel pulse response h(t) (it's the inverse Fourier transform of your frequency response
  2. choose a white band signal x(t), and calculate y(t)=x(t)*h(t) (* is convolution).
  3. from x and y identify your transfer function (you must know the order of your system which is given by your frequency response)

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You have to have both the amplitude and phase information for your system. If you only have the amplitude, you have only half the information you need to reconstruct your system.
when he said frequency response , that means amplitude and phase
True, but we don't know exactly what he has, or what information he can recover from the graph. My intent in my previous comment was to find that out.

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