Differences in Performance Between Simulink and Matlab FIRs
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I am building a BPSK recovery system in Simulink, with the end goal of using the HDL coder to implement it on an FPGA.
I designed the algorithm in MATLAB first, and it works fine. However, translating it to Simulink is giving me trouble.
One of my first steps is to filter my data, which I implemented in MATLAB as
filfir2=fir1(100,[0.000001 8e6/Fs*2]); % Fs=30e6
data = filter(filfir2,1,data); %where data is the raw signal
Implementing the same thing in Simulink however, using the Digital Filter Designer (a 100 tap Hamming window direct form FIR with the same cutoff parameters, resulting in the same Bode plot), gives very different results with the same data:
The orange trace is the data filtered through the Simulink block, and the blue trace is the data filtered through Matlab and brought into Simulink with a From Workspace block.
I also tried
1) Importing my Simulink filter into Matlab and using it in Matlab before sending the filtered data to Simulink
2) Importing my Matlab filter (as a dffir block) into Simulink
Both performed identically to the original Matlab filter (i.e the blue trace).
I am wondering if there is a sample time issue or something where the actual simulation is what's causing the issue?
Thanks!
Ethan M.
![Screen Shot 2019-04-20 at 5.44.09 PM.png](https://www.mathworks.com/matlabcentral/answers/uploaded_files/215103/Screen%20Shot%202019-04-20%20at%205.44.09%20PM.png)
![Screen Shot 2019-04-20 at 5.43.34 PM.png](https://www.mathworks.com/matlabcentral/answers/uploaded_files/215104/Screen%20Shot%202019-04-20%20at%205.43.34%20PM.png)
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Risposte (7)
Bharath Venkataraman
il 22 Apr 2019
I suggest using the the Discrete FIR Filter block with the coefficients you used for MATLAB. If that works, it is the easiest way forward, including for HDL code generation.
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Bharath Venkataraman
il 24 Apr 2019
Could you please pass along a complete script that runs?
I think Fs=30e6 from your comments, but I do not have data defined.
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Bharath Venkataraman
il 24 Apr 2019
Attached is a model where I have taken your coefficients and ran them through fitler and the FIR Filter block. The numbers seem pretty close.
x = randn(1024,1);
Fs=30e6;
filfir2=fir1(100,[0.000001 8e6/Fs*2]);
y = filter(filfir2,1,x);
out = sim('fir_filter_model_18a');
y2 = out.simout.Data(:);
max(abs(y-y2))
figure
plot(y,'y')
hold on
plot(y2,'--r')
hold off
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Ethan Mok
il 17 Mag 2019
1 Commento
Bharath Venkataraman
il 17 Mag 2019
I will take a look at your model.
Right click on my model and chosse teh Save Target as option to download the model.
Ethan Mok
il 17 Mag 2019
1 Commento
Bharath Venkataraman
il 20 Mag 2019
That's great. I have a model here that also shows the numbers are close. Attaching a modified script that shows this.
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