Transmitter noise shaping

This application is concerned with digital to analogue conversion (DAC). In a preferred embodiment it finds application in a direct digital RF modulator (DDRM) of a transmitter in a wireless communications network. In a first embodiment (e.g. Fig. 3) an input digital signal is branched into two. One of the branches is used as an input to a first DAC. The other branch serves as an input to a noise shaping filter. The output of the noise shaping filter is input to a second DAC. The analogue outputs of the DACs are added together. In a second embodiment (e.g. Figures 9 and 13). A digital signal is quantized and the quantized signal undergoes a first DAC. The resulting quantization error undergoes noise shaping and the noise shaped signal input to a second DAC. Again, DAC outputs are summed in the analog domain. The noise shaping may applied to insert a notch at the frequency of a receive signal. The first and second branches may have different sampling rates. The DACs may have different input bit widths, output ranges and resolutions.