plot frequency response of simulink system

Hi guys,

I'm working on digital filter, I have the transfer function of the filter in z-transform and I'm building the filter in simulink using basic models. The problem is I want to know the effect of the fixed point quantization of internal modules (integrators, differentiators, etc...) In other words, I have a reference plot of the targeted transfer function. I need a way to plot the transfer function of the filter built in simulink using basic models. Then I will compare the product transfer function to the reference one.

Is this feasible ? Also I need some advice about the flow I'm using.

I have heard of ltiview tool but it uses S-domain functions not z-transform

Thanks in advance.

Answer 1

[Arkadiy Turevskiy]

There are tools for linearizing Simulink models - i.e., getting a transfer function from a Simulink model. You can take a look our linearization page for that.

What you have to keep in mind though is that transfer functions are used to represent linear time-invariant systems. When you start adding quantization effects and fixed-point scaling in Simulink, you are making your system nonlinear. Think about the most basic example when you represent a signal with either 0 or 1. A small change in the input signal is going to result in either no change in the output signal, or in a jump from one discrete value to another.

In other words, you can linearize a Simulink model using the tools on the page I linked to, but the transfer function is only capturing the linear behavior of the model.

Hope this helps.

Answer 2

[Amr Elhosiny]

Thanks a lot for the linearization concept. I got it.

So, how does the fdatool calculates the filter magnitude response after quantization ?

Answer 3

[Amr Elhosiny]

I want to mention that I used an alternative way that I did not know about. I merged the transfer function in z-domain into the numerator & denominator form. Then I used the import-filter option in the FDA tool. This way I was able to use the fdatool to plot the magnitude and phase response of the filter before and after quantization.