说明：  本文介绍了在数字下变频(DDC) 中的抽取滤波器系统设计方法和具体实现方案。采用CIC 滤波器、HB 滤波器、FIR 滤波器三级级联的方式来降低采样率。通过实际验证,证明了设计的可行性
(This article describes the digital down conversion (DDC) of the decimation filter system design methods and concrete realization of the program. Using CIC filter, HB filter, FIR filter cascade three-level approach to reduce the sampling rate. Through the actual authentication, to prove the feasibility of the design)