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Simple RC filters phase question

  1. May 28, 2010 #1
    1. The problem statement, all variables and given/known data
    I'm a bit confused about how to find the phase equation of a lossy low pass filter
    eg.
    r6yf51.jpg

    2. Relevant equations
    For a normal low pass filter it's just arctan(wRC)



    3. The attempt at a solution

    jja1is.jpg

    So im comparing this by subbing in values and comparing to a bode plot of an actual circuit on a breadboard and a spice version of the circuit. But this is nothing like what i get in spice, i've checked for errors but I think its something wrong with the way im actually calaculating it... but cant figure out why?
     
  2. jcsd
  3. May 29, 2010 #2
    You multplied by the negative of the conjugate. This will screw up your phase equation.
     
  4. May 29, 2010 #3
    Oh thanks so much! Worked out fine now. I feel so stupid haha, i soooo wasn't thinking when i did that! I get the exact same thing except in the last line it's +1 not -1. Makes a big difference though.
     
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