A digital up-converter (DUC) circuit for performing digital channel filtering of an incoming baseband digital signal. The proposed circuit reduces the complexity of the channel module filter of the DUC. This is achieved by taking advantage of the structure of the underlying symbol waveforms carried by the incoming baseband digital signal which have one or more known discontinuities comprising random amplitude and/or phase. Namely, the channel filter module is activated only for the digital samples located around the known discontinuities and is deactivated for the remaining digital samples. Further, the switching of the channel filter module from one state to another can be performed according to a smooth function so that further discontinuities are not introduced in the incoming baseband digital signal. A method and a computer program are also disclosed.