I was just curious as to the differences between the two order filters?
How I created these discrete filters for references
Designed in Continuous first then converted into Discrete
Using Tustin's method as I just want to convert the plant from continuous to discrete
Fc = 20kHZ
Used Prep warping nyquist frequency = 20kHZ (Sampling at Ts = 0.000025/40kHz)
Filter 1: 2nd Order Butterworth filter Analog
Filter 1A: 2nd Order Butterworth Filter Discrete
Filter 2: 1st Order RC Filter Discrete
As you can see in Filter 1A I was shocked to see that "Brick-wall" response and was curious to see what if I used a lower order filter.
In Filter 2 you can see a similar result. The only difference I can tell is that magnitude (dB). The 1st Order filter has a flatter pass band then the 2nd Order Butterworth Filter.
Is there any advantage in using a higher order filter when it comes to discrete? Why in discrete the "Brick-Wall" response is much more apparent now when its only a 2nd Order.
Let me know if I even approached this correctly has I haven't dont discrete in a long time, so I wouldn't be surprise if something went wrong.
Bonus question, why when I try to do a step response for both filters I get this:
Another question that came to mind: Could we use the Sampling time to essentially change the Cut off frequency then?
EDIT: Looks like my Sampling times are wrong no idea what I am doing anymore. How do you know which Sampling Time is suitable for you? Or is that the trade off sacrifice how close it looks to the continuous for sampling times
%% -- Low Pass Filter (LPF) -- %% R1 = 15000; R2 = 9100; C1 = 0.001*10^-6; C2 = 470*10^-12; LPF_A = ((1)/(C2*R1*s + C2*R2*s + C1*C2*R1*R2*s^2 + 1)); opt = c2dOptions('Method','tustin','PrewarpFrequency',125663.706); LPF_D = c2d(LPF_A,0.000025,opt);