z-Transform The contour z=l is a circle in the z-plane of unity radius and is called the unit circle Like the dtft there are conditions on the convergence of the infinite series ∑g[r] 1=-0 For a given sequence, the set r of values of for which its z-transform converges is called the region of convergence ROc) Copyright C 2001, S K MitraCopyright © 2001, S. K. Mitra 5 z-Transform • The contour |z| = 1 is a circle in the z-plane of unity radius and is called the unit circle • Like the DTFT, there are conditions on the convergence of the infinite series • For a given sequence, the set R of values of z for which its z-transform converges is called the region of convergence (ROC)   =− − n n g[n]z