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Topic: [Matlab Question] Converting H(s) to H(z) using derivative approximation?
Replies: 8   Last Post: Dec 7, 2013 3:13 AM

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Posts: 5
From: malaysia
Registered: 10/24/10
Re: [Matlab Question] Converting H(s) to H(z) using derivative approximation?
Posted: Oct 24, 2010 3:11 PM
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Hi Nasser,

thanks for your help.

Sorry i didn't post my workings before. Here is what i actually did in my matlab.

1) I found out the s-roots by using the roots(p) command.

2) then i use the relationship for derivate approximation where z^-1 = 1 - sT.

3) So from s roots, i get the z roots and then i contruct the polynomial from z-roots using the poly(A) command.

4) Then from the polynomial coefficients, i just use freqz to plot the magnitude vs freq response.

Not sure it's 100% right, but when i plot it the shape is correct which is a low pass filter but the magnitude might be a little off.

After seeing your solution, i need to give it a try.

But do you know that the relationship between s and z is as such :

z^-1 = 1 - sT

So when you have such relationship, does your method still holds?

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