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Homework Help: Bandpass Filter Design

  1. Dec 23, 2008 #1
    1. The problem statement, all variables and given/known data

    I have to design a bandpass filter (300Hz to 3000Hz). I have been given a variety of resistors and capacitors to work with.

    Oh yes, another thing is that i need an output voltage that's <8V. I'm cascading it with another IC.

    Capacitors - 10nF, 0.1µF, 0.33µF, 0.47µF, 1µF, 4.7µF, 100µF, 220µF

    Resistors - 100, 330, 1K, 3.3K, 4.7K, 5.6K, 10K, 22K, 47K

    I have tried using my textbooks as a reference and i used a given example. Then i tried working from there on...

    2. Relevant equations

    Some of the formulas given are.. (With reference with my http://img380.imageshack.us/img380/9781/image3kq1.png" [Broken])

    http://www.testdesigner.com/include/math/images/-1926637852.png [Broken]

    http://www.testdesigner.com/include/math/images/639695238.png [Broken]

    3. The attempt at a solution

    I have tried using those formulas, however the best i got was either very small resistance with high capacitance or vice versa.

    Am i doing it the right way?
    Last edited by a moderator: May 3, 2017
  2. jcsd
  3. Dec 24, 2008 #2


    User Avatar

    Since you have 2 equations with 4 unknowns, you must assign arbitrary values to 2 of the unknowns.
    Electrolytic capacitors are not reliable and should be used mainly as bypass or coupling elements.
    I suggest that you choose small values for the capacitors and calculate the value of the resistors.
  4. Dec 24, 2008 #3
    Yep, thanks!

    I used a fixed value of 0.47µF for the capacitance. Got [tex]\approx[/tex] 1K and 100 for the resistances :smile:

    It's just a matter of trial and error i guess.
  5. Jan 4, 2009 #4
    .47mF and 100 ohm give 3388hz which is close, might want to use 0.1mF and some combination of resistors to get closer for you homework!!! Don't know your teacher. You give 90% of the answer might score you 90% of the points!!!:surprised
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