z?t??s?t??Acos?2?fct??Z????A2??S????c??S????c???A2??S????c??S????c???H???
s?t????m?t??Acos?2?fct???*h?t??S?????Z?????A2A2??S????c??S????c????A24???M???2?c??M?????H????c??
4???M????M???2?A2c???H????c??????LPF4M????H????c??H????c??显然滤波器满足以下互补对称特性(5分)
?H??????H???????1,?cc?2?W
显然，在此条件下LPF输出仅与m(t)有关。