A novel sigma delta amplitude modulator having a noise transfer function adapted to shift quantization noise outside at least one frequency band of interest. In one embodiment, the sigma delta amplitude modulator includes a programmable order low pass stage. In a second embodiment, the sigma delta amplitude modulator incorporates comb filtering wherein each comb filter comprises a plurality of fingers to permit greater programmability in the frequency location of notches. A polar transmitter incorporating the sigma delta amplitude modulator is presented that shapes the spectral emissions of the digitally-controlled power amplifier such that they are significantly and sufficiently attenuated in one or more desired frequency bands.