Design of a programmable digital down-converter structure

In this paper we propose a programmable digital down-converter (DDC) structure that can be used in digital receivers that meets GSM or other wireless standards in wireless communications systems. The major advantage of the proposed DDC is that it does not have the passband drop which is very often associated with the cascaded integrator-comb (CIC) based DDCs. Another improvement of the proposed DDC structure compared to the existing off-the-shelf DDC products is that, instead of operating at the input (high) sample rate, the multiplications of the quadrature mixing process are performed at a much lower sample rate.