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Characteristic Polynomial and Angle (Negative Feedback)

  1. Mar 16, 2014 #1
    I hope this is the right place to ask...

    For a close-loop system with negative feedback, the transfer function is

    G(s) / (1 + G(s)H(s))

    where, s is in frequency domain, G(s) is the function of the forward loop, and H(s) is the function of the negative feedback.

    So the characteristic polynomial is

    1 + G(s)H(s) = 0

    Therefore, in polar form, G(s)H(s) has magnitude 1 with argument -180 degrees.

    So why is the standard -180 degrees instead of positive 180 degrees?

    If the net angle of the zeros and poles of GH is positive 180, doesn't it also satisfy the characteristic polynomial?
     
    Last edited: Mar 16, 2014
  2. jcsd
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