乎m z-plane Unit circle xn]=a"uln] 米 1 e z-a 1-az1 o zeros Gray region:ROC ROC:>a x poles pole-zero-plot If |a<1,ROC includes the unit circle,DTFT of x[n]is uniform convergence. 1515 : zeros  : poles Gray region: ROC     n x n a u n = ( ) z X z z a = − ROC z a :  1 1 1 az = − − pole-zero-plot If |a|<1, ROC includes the unit circle, DTFT of x[n] is uniform convergence