Script not producing the correct plot

Question

José Carlos Ferreira 2014-9-12

0
链接

此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/154584-script-not-producing-the-correct-plot

编辑： José Carlos Ferreira 2014-9-13

采纳的回答： Star Strider

在 MATLAB Online 中打开

Hi...

I need to simulate a signal in MatLab but I can't make my simple script to work properly.

The function is a Transfer Function of a given circuit.

The expression is the following

The script I'm trying to use to simulate this expression is:

    if true
R1=100;
R2=1e3;
C=1e-6; 
% fc=1/(2*pi*R*C); 
f=1:1:1e4; 
ter1=R2^2;
ter2=(2*pi.*f*C*R1*R2).^2;
ter3=(R1+R2).^2;
ter4=(2*2*pi.*f*C*R1*R2).^2;
mhf=(ter1+ter4)/(ter2+ter3); 
mhf=power(mhf, 0.5);
% mod_hf=abs(hf); 
% fase_hf=angle(hf); 
figure(1); 
subplot(2,1,1); plot(f,mhf); grid on; 
title('Funcao de Transferencia do Filtro Passa-baixo RC') 
xlabel('Frequencia (Hz)') 
ylabel('|H(f)|') 
% subplot(2,1,2); plot(f,fase_hf);grid on; 
% xlabel('Frequency (Hz)') 
% ylabel('arg[H(f)] (rad)') 
    end

I have calculated the result for a few frequencies in calculator and I fot the following values:

f=0Hz--> |H(f)| = 0.9091
f=50Hz--> |H(f)| = 0.9081
f=200Hz--> |H(f)| = 0.8932
f=500Hz--> |H(f)| = 0.8274
f=1000Hz--> |H(f)| = 0.7072
f=5000Hz--> |H(f)| = 0.5169
f=5MHz--> |H(f)| = 0.5

which matches an High-Pass Filter but I can't get the correct plot!!! Any help?

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Answer 1

Star Strider 2014-9-12

2
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/154584-script-not-producing-the-correct-plot#answer_151558

在 MATLAB Online 中打开

Change:

mhf=(ter1+ter4)/(ter2+ter3);

to:

mhf=(ter1+ter4)./(ter2+ter3);

and it works. You need to do element-by-element division as well.

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Star Strider 2014-9-13

No matter how I analyse that circuit, I get a lowpass characteristic out of it. I can’t reproduce your result.

Stopping here.

José Carlos Ferreira 2014-9-13

编辑：José Carlos Ferreira 2014-9-13

If you try to calculate a few values for H(f) and for H(f) phase in a calculator, are your calcs consistent with MatLAb?

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Answer 2

José Carlos Ferreira 2014-9-12

0
链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/154584-script-not-producing-the-correct-plot#answer_151560

在 MATLAB Online 中打开

I've changed a little bit the script to use the original Transfer Function and let MatLab compute the Abosulte and Angle values for it but I can't understand why the results from MatLab are not consistent with my calculator results...

R=2.2e3; 
C=0.33e-6; 
fc=1/(2*pi*R*C); 
f=1:1:1e5; 
hf=(R2+j*2*pi.*f*C*R1*R2)./((R1+R2)+j*2*pi.*f*C*R1*R2); 
mod_hf=abs(hf); 
fase_hf=angle(hf); 
figure(1); 
subplot(2,1,1); plot(f,mod_hf); grid on; 
title('Funcao de Transferencia do Filtro Passa-baixo RC') 
xlabel('Frequencia (Hz)') 
ylabel('|H(f)|') 
subplot(2,1,2); plot(f,fase_hf);grid on; 
xlabel('Frequency (Hz)') 
ylabel('arg[H(f)] (rad)')