The Efficient Design and Modification of Cascaded Integrator Comb Filter

Abstract

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 radio remote unit (RRU) system. Then a compensation technique, 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. However, this kind of filter will reduce the attenuation in stop-band at the same time. In order to deal with this problem, this paper proposes Cosine filter, which is cascaded before CIC-ISOP to implement pre-filtering. By analyzing frequency characteristics, this cascaded filter enlarges the attenuation in stop-band and sharpens the transition band. With this method, we can obtain the improved and ideal magnitude response, and the results of this approach come up to the requirements of GSM RRU system.