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

Difference equation vs differential equation

  1. Oct 12, 2009 #1

    Im trying to go back and relearn material from a signals class I took to prepare for my controls class.

    In the controls class we always deal with CT systems, whereas in the systems class we focused on DT.

    My prof derived a frequency response that was H(w) = 1/(1-a*exp(i*w)).

    This dint look farmiliar as in my controls class we never have exponentials in the frequency response.

    The complex exponential in the Freq response came from y(n) = y(n-1) + x(n), more particularly the y(n-1) part. Now im guessing the reason this doenst look farmiliar to my controls work is that we always use CT in controls, so there will never be a y(n-1) in our answer. So my question is: What is the CT parallel for the DT term y(n-1)? What makes a CT model have a complex exponential in the solution (aside from actually having y(t) = y(t-1), as y(t-1) doesnt mean the same thing in DT as CT)?

  2. jcsd
  3. Oct 21, 2009 #2
    no one?
  4. Oct 21, 2009 #3
    i think that the i.f t is coming from ..
    so take f.t
    That's it i think where exp comes where no unit step function is found here
    any question again if you need ...
    Last edited by a moderator: Oct 21, 2009
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook