Hello there,It is not true that you want to match source and load impedances in a filter. You want the impedance to be such that you get the desired characteristic; in this case maximally flat in the passband and less than or equal to some value in the transition band. Impedance matching is primarily done to transfer the maximum amount of power from the source to the load. In most filtering applications power transfer is irrelevant.
The problem with impedance matching in a typical lowpass filter is the large bandwidth you need to deal with. Maybe in a bandpass or a notch filter you have a better chance of of doing it without changing the filter characteristic. Adding a cap to a Butterworth filter is like riding on a see-saw, it may improve something, but at the expense of something else.Hello there,
Well, i have to tell you i think that's the first time i ever heard that because filters are used all the time for matching purposes.
At these frequencies maybe, but add another cap for an input cap and guess what we end up with ... a Low Pass impedance matching filter
The way this was worded it sounded at first like they wanted to match the input and output impedance too, but that is only possible with a compromise without adding the second cap, but then we get a low pass filter that also matches input to output.
Maybe at 1kHz it would be a bit rare. At 100kHz and up more likely. But with these academic type problems you never know what they want.
Hi again,The problem with impedance matching in a typical lowpass filter is the large bandwidth you need to deal with. Maybe in a bandpass or a notch filter you have a better chance of of doing it without changing the filter characteristic. Adding a cap to a Butterworth filter is like riding on a see-saw, it may improve something, but at the expense of something else.
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