Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Can you offer guidance or do you also need help?
Draft saved Draft deleted