# Matlab bode plot with specific cut off frequency

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Aaron Frost il 21 Feb 2023
Commentato: Star Strider il 21 Feb 2023
This scrip displays a bode diagram however the cut off frequency is incorrect. I need the cut off frequency to be 15kHz whilst showing the gain to be 27dB. Does anyone have an idea how I can achieve this? Thank in advance.
clc
format long
C1 = 0.000000000150;
C2 = 0.000000000470;
R1 = 10000;
R2 = 180000;
R3 = 2700;
R4 = 56000;
G = (R3+R4)/R3;
A = 1/(C1*R2)
B = 1/(C2*R2)
C = (1/(C1*R1))*(1-G)
D = 1/(C1*C2*R1*R2)
E = (A+B+C)
%{
Numerator = {[G 0 0] };
Denominator = {[1 0] [A] [B] [C] [0 D]};
T = tf(Numerator, Denominator)
Numerator = {[G 0 0] };
Denominator = {[1 (A+B+C) D]};
T = tf(Numerator, Denominator)
%}
%{
T = tf([G 0 0], [1 (A+B+C) D]);
%}
%T = tf([21.740 0 0], [1 1.418439716*10^4 5.263157895*10^-6]);
T = tf([G 0 0], [1 E D]);
%T = tf([21.740740740741 0 0], [1 -13778303.125821 7880220646.1781])
options = bodeoptions;
options.FreqUnits = 'Hz'; % or 'rad/second', 'rpm', etc.
bode(T,options);
grid on
Im looking to achieve something like this.
##### 0 CommentiMostra -2 commenti meno recentiNascondi -2 commenti meno recenti

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### Risposte (1)

Star Strider il 21 Feb 2023
The easiest option may be to define the radian frequency function:
w = linspace(0, 1.5E+4, 1E+3)*2*pi;
and then supply it as an argument to bode
clc
format long
C1 = 0.000000000150;
C2 = 0.000000000470;
R1 = 10000;
R2 = 180000;
R3 = 2700;
R4 = 56000;
G = (R3+R4)/R3;
A = 1/(C1*R2);
B = 1/(C2*R2);
C = (1/(C1*R1))*(1-G);
D = 1/(C1*C2*R1*R2);
E = (A+B+C);
%{
Numerator = {[G 0 0] };
Denominator = {[1 0] [A] [B] [C] [0 D]};
T = tf(Numerator, Denominator)
Numerator = {[G 0 0] };
Denominator = {[1 (A+B+C) D]};
T = tf(Numerator, Denominator)
%}
%{
T = tf([G 0 0], [1 (A+B+C) D]);
%}
%T = tf([21.740 0 0], [1 1.418439716*10^4 5.263157895*10^-6]);
T = tf([G 0 0], [1 E D]);
%T = tf([21.740740740741 0 0], [1 -13778303.125821 7880220646.1781])
w = linspace(0, 1.5E+4, 1E+3)*2*pi;
options = bodeoptions;
options.FreqUnits = 'Hz'; % or 'rad/second', 'rpm', etc.
bode(T,w,options);
grid on
.
##### 2 CommentiMostra NessunoNascondi Nessuno
Aaron Frost il 21 Feb 2023
Sorry I forgot to mention that I need to gain to be visible showing 27dB
This is what im looking to achieve but it needs to be with matlab
Star Strider il 21 Feb 2023
Try something like this —
% clc
format long
C1 = 0.000000000150;
C2 = 0.000000000470;
R1 = 10000;
R2 = 180000;
R3 = 2700;
R4 = 56000;
G = (R3+R4)/R3;
A = 1/(C1*R2);
B = 1/(C2*R2);
C = (1/(C1*R1))*(1-G);
D = 1/(C1*C2*R1*R2);
E = (A+B+C);
%{
Numerator = {[G 0 0] };
Denominator = {[1 0] [A] [B] [C] [0 D]};
T = tf(Numerator, Denominator)
Numerator = {[G 0 0] };
Denominator = {[1 (A+B+C) D]};
T = tf(Numerator, Denominator)
%}
%{
T = tf([G 0 0], [1 (A+B+C) D]);
%}
%T = tf([21.740 0 0], [1 1.418439716*10^4 5.263157895*10^-6]);
T = tf([G 0 0], [1 E D]);
%T = tf([21.740740740741 0 0], [1 -13778303.125821 7880220646.1781])
w = logspace(-3, log10(1.5E+8), 1E+3)*2*pi;
options = bodeoptions;
options.FreqUnits = 'Hz'; % or 'rad/second', 'rpm', etc.
bode(T,w,options);
grid on
Fx = gcf;
Kids = Fx.Children;
MagPlot = Kids(3);
YdB = MagPlot.YLim
YdB = 1×2
-3.000000000000000 0.267445587351631
Ymag = db2mag(YdB)
Ymag = 1×2
0.000000000000001 21.738418068660366
.

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