Home › Forums › temp › Variable Gain Bandpass Filter That Uses Only One Op-Amp › Filters
Total posts : 45366
I don’t recognize that circuit in the link so I can”t be of much use. I will mention that it is difficult to get a stable filter with so few parts. They tend to ring and oscillate.
I think a much better approach will be to use the Sallen and Key circuit. This requires two stages cascaded, but the parts count is reasonable.
The bandpass is adjusted by setting the Fc’s, one for the high cutoff and the other for the low cutoff. This is done by choosing capacitors and calculating the resistances, or if using pots, the cutoff frequencies can be variable.
Floyd’s “Electronic Devices” textbook covers this topic quite well. It is very often used in Tech Schools and you will probably find a copy in the Library or on a Professor’s bookshelf.
Though I have not tried it, a web search on “Sallen and Key” , “Butterworth”, “Chebyshev”, or “active filters” will probably provide something you can use.