Sunday, November 3, 2019

How to find system function, H(z) in the z-domain, given zero-pole plot of the system?



I'm given a zero-pole plot (Real/Imaginary Plane) of a system in which poles occur at $\frac{-9}{10}$, $\frac{9}{10}$, and zeros occur at $\frac{10}{9}j$, $\frac{-10}{9}j$. An additional zero occurs at negative infinity.


I'm also given that $H_{F}(f)=1$ for $f=0$, where $H_{F}(f)$ refers to $H(z)$ for when $z=e^{-j 2\pi f}$. I'm tasked to find $H(z)$.


I know I can express $H(z)$ as $$H(z)=G_0z^{-1}\frac{(z-z_0)(z-z_1)\ldots}{(z-p_0)(z-p_1)\ldots} $$ for zeros $$z_0,z_1,\ldots$$ and poles $$p_0, p_1,\ldots$$


I can find the constant $G_0$ by using the fact $H_{F}(f)=1$ for $f=0$.


I'm unsure how to express the fact that the system has a zero at negative infinity.




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