7.0 introduction ideal frequency selective filter 2其-c2Ⅱ c 2 (a)理想低通 (b)理想高通 H(eJ° C 2其 2 (c)理想带通 (①理想带隕 band-stop filter: notch filter; quality factor of band-pass filter=pass-band width/ center frequency7.0 introduction ideal frequency selective filter band-stop filter：notch filter；quality factor of band-pass filter=pass-band width/center frequency