# Designing bandpass filters for harmonics Project

#### PMB917

Joined Mar 7, 2006
5
I'm putting together a project for school (ITT Tech Woburn MA) that deals with harmonics of certin tyes of waves. (square, triangle,sawtooth ect.) I need to design variable gain bandpass filters for 2kHz, 4kHz, 6kHz, 8kHz and 10kHz.

There are a few ways to do this, and I've found one way to do this with only one op amp.

http://www.elecdesign.com/Files/29/4481/Figure_01.gif

The only problem here is that they dont give any formulas for setting the center frequency or Q.

Anyone farmilure with this design?

I also had another thought to use a multiple feedback bandpass filter design.
http://www.captain.at/electronics/active-filter/
But that would mean I'd need twice the number of op amps to be able to vary the gain.

I could go sallen key but then I'd be upto 3 op amps per harmonic totaling 14 and theres only so much room on a breadboard.

anyone got suggestions?

#### aac

Joined Jun 13, 2005
35
Originally posted by PMB917@Mar 7 2006, 08:09 PM
I'm putting together a project for school (ITT Tech Woburn MA) that deals with harmonics of certin tyes of waves. (square, triangle,sawtooth ect.) I need to design variable gain bandpass filters for 2kHz, 4kHz, 6kHz, 8kHz and 10kHz.

There are a few ways to do this, and I've found one way to do this with only one op amp.

http://www.elecdesign.com/Files/29/4481/Figure_01.gif

The only problem here is that they dont give any formulas for setting the center frequency or Q.

Anyone farmilure with this design?

I also had another thought to use a multiple feedback bandpass filter design.
http://www.captain.at/electronics/active-filter/
But that would mean I'd need twice the number of op amps to be able to vary the gain.

I could go sallen key but then I'd be upto 3 op amps per harmonic totaling 14 and theres only so much room on a breadboard.
anyone got suggestions?
[post=14763]Quoted post[/post]​
The circuit you posted looks like a version of a twin-t filter. I'm sure you can find the formulas quickly if you do a search on twin-t bandpass.