DIGITAL TIME ALIGNMENT IN A POLAR MODULATOR

摘要

Methods of and apparatus for digitally controlling, with sub-sample resolution, the relative timing of the magnitude (101a) and phase (101b) paths in a polar modulator. The timing resolution is limited by the dynamic range of the system as opposed to the sample rate. The methods and apparatus of the invention use a digital filter (111) to approximate a sub-sample time delay. Various techniques for approximating a sub-sample time delay using digital signal processing may be used to achieve the approximation. Ideally, the filter will have an all-pass magnitude response and a linear phase response. In practice, the magnitude may be a low-pass and the phase may not be perfectly linear. Such deviation from the ideal response will introduce some distortion. However, this distortion may be acceptably small depending on the particular signal being processed.