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Homework Help: 2nd order Passive LPF

  1. Sep 23, 2007 #1
    This isn't really an exact homework problem since it's for a report I'm doing. Basically, I was wondering what the design for a second order passive low pass filter looks like. I know how to design a regular first order circuit but I have no clue about a second-order PASSIVE LPF. I tried just cascading two RC circuits and using 1/(2pi(RC)) to define the cutoff frequency but after simulating it on my computer, the actual cutoff is quite off. Anyone have any insight into this?? Thanks in advance.
  2. jcsd
  3. Sep 23, 2007 #2
    Why do you want to make a passive filter? Take my advice and use an active filter. The techniques for making active filters using op amps is very mature and you can get whatever gain you wish. Look for the book on the web (its free!): "Digital Signal Processing" by Steven Smith. Look on page 50 for a good discussion on analog filters and a simple design table.
  4. Sep 23, 2007 #3
    Believe me, I would, but it tells me to make a 2nd order passive LPF in the assignment. Thanks though.
  5. Oct 24, 2009 #4
    Shame there was no answer to this forum :( Im stuck now too I have to do a 3rd order high pass RC active filter though
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