Can't find inverse Z transform

  • Thread starter Thread starter Addez123
  • Start date Start date
  • Tags Tags
    Inverse Transform
Addez123
Messages
199
Reaction score
21
New poster has been reminded to use the Homework Help Template when starting threads in the schoolwork forums

Homework Statement


I got the laplace transfer function H(s) = 1/(s + 2) and I'm suppose to find the inverse Z transform by first converting to H(z) by s = Ts/2*(z-1)/(z+1)
Then do inverse Z-transform using the "displacement rule" - Never heard of.

Homework Equations


H(s) = 1/(s + 2)
s = Ts/2*(z-1)/(z+1)

3. The Attempt at a Solution

I can't get any serious answer, and the partial z-inverse that I manage to find it's incredibly complicated (see image).
Namnl_s.png

What is this 'displacement rule' and how do I use it here?
 
Last edited:
Physics news on Phys.org
I don't have reference 17 (James G. Advanced modern engineering mathematics. Reading: Addison-Wesley; 1993.) that they refer to, but it looks like this paper ( https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5240402/ ) uses it to associate the scaled/shift inside δ(γk-λtot(t)) of equation 13 with (1/γ)ztot(t)/γ in equation 15.
Conversions like that are fairly common in transformations involving the delta function.
 
The solution was to, after replacing 's' with the Z components, then put all under one fraction sign (no plus in nominator). Then multiply with Z^-1 in bottom and top until you got only Z^- terms. This = Y(x)/X(x) which can then be translated back to y[n] and y[n-1] = Z^-1*Y(x)
 
There are two things I don't understand about this problem. First, when finding the nth root of a number, there should in theory be n solutions. However, the formula produces n+1 roots. Here is how. The first root is simply ##\left(r\right)^{\left(\frac{1}{n}\right)}##. Then you multiply this first root by n additional expressions given by the formula, as you go through k=0,1,...n-1. So you end up with n+1 roots, which cannot be correct. Let me illustrate what I mean. For this...
Back
Top