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Electronics Forum / Basics / December 2005Low Pass Filter basics
I have a question about low pass filters. I am designing a 2nd order lo pass LC filter. What determines the response type? (ie. butterworth bessel, etc.) Many thanks, Paul > I have a question about low pass filters. I am designing a 2nd order low > pass LC filter. What determines the response type? (ie. butterworth, > bessel, etc.) Active or passive ? Graham Search google for filter software, there is a ton of it which may help with your design stuff. Some of it if very good and best most that I recall was F R E E! > I have a question about low pass filters. I am designing a 2nd order low > pass LC filter. What determines the response type? (ie. butterworth, > bessel, etc.) > > Many thanks, > Paul toyo22r: What determines the response type? (ie. butterworth, bessel, etc.) ==================== Response has to do with damping... this is controlled by Q of the coil Q=omegaL/R, f=1/(2*pi*R*C) > toyo22r: > What determines the response type? (ie. butterworth, > bessel, etc.) > ==================== > Response has to do with damping... this is controlled by Q of the coil > Q=omegaL/R, Not alone. The load on the filter affects the damping too. ( in the case of an active filter the gain ). Graham Sorry. Too early. that f was for an RC filter. For the LC filter f=1/(2*pi*sqrt(LC)) > I have a question about low pass filters. I am designing a 2nd order low > pass LC filter. What determines the response type? (ie. butterworth, > bessel, etc.) > > Many thanks, > Paul The various response types emphasise certain filter features, such that one chosen style may offer a little extra benefit in a particular filtering job. (You) make the choice based on knowing what flavours are available (there's about half a dozen kicking about) and the particular properties that they each advertise. Feature wise, there's not a great deal to mug up on but I can't offhand suggest a [useful] filter website as I've not seen one and most filter textbooks lose the plot after about page 1. At the end of the day, a LP filter is a LP filter and a design that gives components calculated for a Butterworth style response (feature: flat response upto it's cutoff) can be OK for maybe 90% of all day to day filtering needs. All the rest is just niceties :) regards john > I have a question about low pass filters. I am designing a 2nd order low > > pass LC filter. What determines the response type? (ie. butterworth, > > bessel, etc.) Look here: http://www.dspguide.com/pdfbook.htm Chapter 3 has a nice explanation of antialias filters, and gives a good description of the different types of filters.  SignatureRegards, Bob Monsen A great discovery solves a great problem, but there is a grain of discovery in the solution of any problem. Your problem may be modest, but if it challenges your curiosity and brings into play your inventive faculties, and if you solve it by your own means, you may experience the tension and enjoy the triumph of discovery. - George Polya |
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