电子科发女学光电科学与工程学院 SCHOOL OF OPTOELECTRONIC SCIENCE AND ENGINEERING OF UESTC 3.Impulses and Their Sifting Property The unit discrete impulse FIGURE 4.2 A unit discrete impulse located at x=xo.Variable x is discrete,andδ is 0 everywhere except at x xo. -Sifting property 8(x-xo) ∑f(x)6(x)=f(0),x=0 ∑f(x)6(x-)=f(x),x=x-( ) 1, 0 , 0, 0 x x x   = =    ◼ Sifting property 3. Impulses and Their Sifting Property ( ) ( ) (0), 0 x f x x x  f  =−  = = ( ) ( 0 0 ) ( 0 ), x f x x  x x x f x  =−  − = = ◼ The unit discrete impulse . . 1 ( ) x s t x   =−  =