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Low Pass Filter basics

Discussion in 'Electronic Basics' started by toyo22r, Dec 29, 2005.

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  1. toyo22r

    toyo22r Guest

    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
     
  2. Pooh Bear

    Pooh Bear Guest

    Active or passive ?

    Graham
     
  3. 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!
     
  4. BobG

    BobG Guest

    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)
     
  5. BobG

    BobG Guest

    Sorry. Too early. that f was for an RC filter. For the LC filter
    f=1/(2*pi*sqrt(LC))
     
  6. Pooh Bear

    Pooh Bear Guest

    Not alone. The load on the filter affects the damping too. ( in the case
    of an active filter the gain ).

    Graham
     
  7. john jardine

    john jardine Guest

    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
     
  8. Bob Monsen

    Bob Monsen Guest

    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.

    --
    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
     
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