SIGMA-DELTA IF A-D CONVERTERS FOR DIGITAL RADIOS

The advantages of digitally encoding the IF signal in a heterodyne radio receiver are considered, and include improved discrimination between upper and lower sidebands, reduced spurious carrier component and the removal of flicker noise in the demodulated signal Bandpass sigma delta converters are well suited to this task because of the nan ow channel bandwidth to IF ratio and the requirement for high linearity The concept of sigma delta conversion is explained at a fundamental level and examples of higher order advanced architectures ave presented. A mapping between baseband and digital modulator architectures is presented, allowing bandpass converters to be designed from their baseband equivalents. Finally a discrete component implementation of a converter is presented with art overview of the performance obtained in practice. The converters, implemented with discrete components and LC filter stages, have been successfully developed at the GEC-Marconi Research Centre and ave currently being designed into a variety of receivers by several GEC product companies.