How to design a 10kHz- 90KHz bandpass Butterworth filter using MAX275? And how to determined the resistances using MAXIM FILTER DESIGN SOFTWARE and analitically??
I think you need to know about the analog filter design.Analog active filter design can be found in the book : Analog and digital filter design by winder. I myself use it to design active filters. When you grasp in the filter you will easy follow the instructions by the Maxim to design their filters for a given application.
Best wishes
Maxim has gotten all sorts of ressources for this chip. Start at
https://www.maximintegrated.com/en/products/analog/analog-filters/MAX275.html and go to the tab "DESIGN RESOURCES". The datasheet gives what's required for an "analytical" solution.
Considering your specification (10 - 90 kHz pass band), I'd expect that you won't be too happy with the outcome of a band pass implementation. (I get a Q not higher than 0.5 for your specs.)
A better approach might be to implement 2 low pass filters (10 resp. 90 kHz cutoff) and combine the outputs with a separate OpAmp.
How are you Dr. Dreher?
Hope you are well.
I am sure that you mean a series combination of a low pass filter cutting at fc=90 kHz and a high pass filter cutting at 10 kHz.
I agree with you completely. This is the way to implement this wide band bandpass filter.
If the two low pass filters are used then the have to be connected in parallel and then one subtracts the output of the 10kHz filter from the output of the 90 kHz low pass filter. In this way one has to use one extra difference amplifier.
Best wishes
Hello Prof. Zekry,
I'm fine so far (although still recovering from a bad cold). How are you?
You clearly got the concept:
- implement 2 parallel low-passes (10 resp. 90 kHz) (The MAX275 is not designed to implement high-passes.)
- Use an external OpAmp as an adder - subtracting the 10 kHz low-pass filtered signal from the the 90 kHz low-pass filtered signal. Subtracting the 10 kHz lowpass filtered signal from the input (or another signal containing at least the whole spectrum up to 10 kHz) effects a high-pass with a cut-off frequency of 10 kHz. (Following the insight that a high-pass could be implemented by subtracting the low-pass filtered signal from the original signal.)
Have a nice day.
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