Frequency-Selective Filters Ideal lowpass filter(discrete-time system) W<w 0,1。<lw<兀 SIn w n 0<n<O 元- 2丌7 Frequency-Selective Filters ◆Ideal lowpass filter (discrete-time system) ( )       = w w  w w H e c j w c l p 0, 1, 0 wc − 2 − − wc  2 ( ) jw H e 1 ( ) = −   n   n w n h n c l p , sin 