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 An unit discrete impulse train sa(d)=∑6(t-nAT) X=-00 5Ar(0 FIGURE 4.3 An ·-3AT-2△T-△T0 △T 2AT 3AT .. impulse train.3. Impulses and Their Sifting Property ◼ An unit discrete impulse train ( ) ( ) T x s t t n T    =− = −  