Script not producing the correct plot

2014 9 12
2 个回答
回答已采纳
更新时间：2014 9 13
1 次查看（30 天）

0 个投票

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?

请先登录，再回答此问题。

 采纳的回答

Star Strider
Star Strider 2014-9-12

2 个投票

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.

5 个评论
显示 3更早的评论 隐藏 3更早的评论

Star Strider
Star Strider 2014-9-12
José Carlos Ferreira’s ‘Answer’ moved here:
Ok, it's working but it's not consistent with results from calculator...
It should start around 0.9091 for f=0Hz and stabilize around 0.5 for high frequencies!!! And the plot is starting around 0.9 and goes up until 2...
Star Strider
Star Strider 2014-9-12
I would have to see your circuit and analyse it myself to see if there is a problem. You coded your equation correctly with respect to the equation you posted as far as I can determine.
Ok, I'll try to represent it here:
____R1____
________| |______________________________o
|_____C1___| |
__|__
| |
| |
R2 C2
| |
|_____|
|
____________________________|_____________________o
Where C1 = C2 = 1uF and R1 = 100 ohms and R2 = 1000ohms
Star Strider
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
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?

请先登录，再进行评论。

更多回答（1 个）

0 个投票

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)')

2 个评论
显示 无 隐藏 无

José-Luis
José-Luis 2014-9-12
Please don't place a comment as a new answer.
This was not a comment. Was actually a new reply... I'm not very used to this kind of forum! Sorry!

请先登录，再进行评论。

类别

在 帮助中心 和 File Exchange 中查找有关 Signal Operations 的更多信息

标签

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by