Function "lowpass()" Behavior Dependent on Sampling Rate?

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Anyu
Anyu 2024-9-20
评论： Anyu 2024-9-20
Hi folks,
I'm trying to determing the bandwidth of amplifier I'll need, as part of control system.
So I wrote up a simulator script and got this waveform:
Fig.1: Waveform from simulator output
Then I tried to apply a lowpass filter to the waveform, and see how the signal will be warped by the limited bandwidth.
I tried to use the "lowpass()" function provided in the signal processing toolbox:
Fig.2: Call of the lowpass function
Here comes the wierd part, the output do not change when I changed the variable "bnd_f", which should be the cut-off frequency. But when I changed the simulator time resolution (i.e. 1/sampling rate), the output from "lowpass()" changed.
Fig.3: The changed value res_t is highlighted
Fig.4: Resolution = 1ns
Fig.5: Resolution = 5ns
Fig.6 Resolution = 10ns
I'm so confused by what's going on. Any suggestion is highly appreciated!
Many Thanks,
Anyu
  1 个评论
Anyu
Anyu 2024-9-20
Seems like I posted the wrong picture for Resolution = 5ns, here's the correct one:
Replace Fig.5: Resolution = 5ns

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回答（1 个）

Rishav
Rishav 2024-9-20
Hi Anyu,
Yes, the 'lowpass' function in MATLAB is dependent on the sampling rate of the input signal.
Please refer to the following documentation to know more about the 'lowpass' function:
https://www.mathworks.com/help/releases/R2023a/signal/ref/lowpass.html
  1 个评论
Anyu
Anyu 2024-9-20
Thank you for your reply!
In that case, can you please suggest some way I can test the impact of bandwidth on the signal? The target signal is output from simulator, and contained in a 1x20001 vector in workspace.
Thank you very much!

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