The design of CIC filter for the GSM RRU system
Tao Zhou · Journal of Zhejiang University of Technology · 2011
The traditional cascaded integrator comb(CIC) filter is introduced at first,and its pass-band attenuation and mirror-aliasing can not meet the requirements of the GSM RRU system.Then a compensation technique of CIC,Interpolated Second Order Polynomial(ISOP) method,is studied to improve the frequency response of the traditional CIC filter,which can enhance the performance in pass-band but also reduce the attenuation in stop-band at the same time.So there are still some problems in this kind of filter.In order to deal with these problems,this paper proposes an improved way,in which Cosine filter is cascaded before compensation filter to implement pre-filtering.By analyzing the frequency characteristics,this cascaded filter enlarges the attenuation in stop-band and sharpens the transition zone.It can satisfy the requirements of GSM RRU system.