Bode Plot Matlab Homework: High Pass Filter

[roam]

Homework Statement

I'm trying to make a theoretical Bode plot of a High pass filter (made up of a capacitor and a resistor). The transfer function is:

$T=\frac{V_{out}}{V_{in}}= \frac{R}{R+1/(j\omega C)} = \frac{1}{1-j\omega_0 / \omega}$

With a corner frequency of 5 kHz or in radians:

$\omega_0 = \frac{1}{RC} = \frac{1}{(1440.96 \Omega)(22 \ nF)}$

The Attempt at a Solution

I rewrote the transfer function as:

$\frac{s}{s+\omega_0}$ where s=jω

And used the following code:

w=1/(1440.96*(22e-9))

N=[1];
D=[1 w];
sys = rss(5);
h = bodeplot(sys);
setoptions(h,'FreqUnits','Hz','PhaseVisible','off');
h=bode(N,D);

And here is what I got:

Clearly this is wrong, it is not the graph of a high-pass filter. Here is my experimental result (how the curve should look like):

So what is wrong with my code?

Any help is greatly appreciated.

 

[milesyoung]

MATLAB usually expects that when you're working with transfer functions, they're expressed in the complex variable of the Laplace transform. You can make things easier for yourself if you instead use:
$$\frac{V_\mathrm{out}}{V_\mathrm{in}} = \frac{R}{R + \frac{1}{s C}}$$
Both commands 'bodeplot' and 'bode' expect an argument of 'Dynamic System Model' type. Here's a trick you can use to make your code more readable when creating these objects:

s = tf('s');
sys = R/(R + 1/(s*C));

Maybe give that a try.

 

[roam]

Thank you so much for the prompt reply. I modified my code as you instructed, and the resulting curve looks correct (I get the 5kHz corner frequency where required). :)

 

[jhae2.718]

I'm late to the party, but the problem is you've defined the transfer function incorrectly.

N=[1];
D=[1 w];

will produce$$\frac{1}{s+\omega_0};$$to get the desired TF of$$\frac{s}{s+\omega_0}$$you need to do

N=[1 0];
D=[1 w];

The vectors defining the numerator and denominator of the TF are descending powers of $s$, so you need $[s^1\;s^0]$.

 

[rezeew]

Based on your transfer function and corner frequency, it looks like your code is correct. However, there are a few things to note. First, make sure you are using the correct units for your frequency (Hz or rad/s). Also, check to see if there are any typos in your code or if you are missing any necessary functions. Additionally, it could be helpful to plot the magnitude and phase separately to see if there are any discrepancies. Finally, make sure your experimental result is accurate and matches the expected response for a high-pass filter. If you are still having trouble, try reaching out to a classmate or your instructor for further assistance.