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
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18 years ago
Low Pass Filter basics
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18 years ago
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)
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18 years ago
Sorry. Too early. that f was for an RC filter. For the LC filter f=1/(2*pi*sqrt(LC))
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18 years ago
Active or passive ?
Graham
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18 years ago
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18 years ago
Not alone. The load on the filter affects the damping too. ( in the case of an active filter the gain ).
Graham
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18 years ago
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
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18 years ago
Look here:
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Chapter 3 has a nice explanation of antialias filters, and gives a good description of the different types of filters.
-- Regards, 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