2丌1 TX(k) X(k) X N FT NT=T y 0 x(n) 1 x(k) 0 NNTs = T 0 2 N 2 N − 1 ( ) 2 1 ( ) X k N T X k s   = 3 ( ) 0 x = x t 0 N n x(n) 0 2 N 2 N − 1 N X (k) Ts 1 FT FT