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This paper presents a new modified cascaded integrator comb (CIC) decimation filter with sharpened magnitude response which is base on amplitude change function, although pass-band droop and stop-band attenuation are reduced greatly, there exists little pass-band droop over signal bandwidth. For the sake of compensating pass-band droop, a compensation filter based on least square criterion is advanced, the coefficients of the compensation filter are obtained by solving two simple linear equation. The proposed filter is the cascade of the sharpened modified CIC filter and compensation filter, which plays an important role in digital down conversion circuit of the Global Navigation Satellite System (GNSS) receiver based on software defined radio (SDR). With the help of the proposed filter, acquisition and tracking circuit can work at lower frequency and would be easy to implement.