基于DSPbuilder搭建的DDC，里面包括CIC滤波器，FIR低通滤波器，HB半带滤波器，NCO等，实现了GC5016芯片的功能-DSPbuilder erected based on DDC, which include the CIC filter, FIR low-pass filter, HB half-band filter, NCO, etc. to achieve the function of the GC5016 chip

nco + cic + ddc 数字下变频抽取滤波的基础步骤，代码已通过调试-nco+ cic+ ddc