Transfer function from a frequency response graph

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

Answer 1

[Arkadiy Turevskiy]

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

[Shmuel Nedjar]

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

Answer 2

[Azzi Abdelmalek]

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)

[Rodrigo Trigona]

I have only a graph of a frequency response. I don't know the order of my system.

[Azzi Abdelmalek]

if your system is linear, if H(w) is your frequency response,

1. plot 20*Log10(H(w)) with log axis (bode diagram)
2. if the drop in db is 20*n then your order system is n

[Star Strider]

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.

[Azzi Abdelmalek]

when he said frequency response , that means amplitude and phase

[Star Strider]

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.