RECEIVER WITH ANALOG AND DIGITAL CHANNEL SELECTIVITY

摘要

A radio receiver for receiving radio frequency (RF) signals includes an analog down-converting and filtering section for down-converting and selecting the RF signals to an intermediate passband and a stopband which substantially determine the widest bandwidth of operation of the radio receiver. An analog-to-digital converter converts the intermediate frequency signal to a sampled digital signal. A digital filtering section, responsive to the sampled digital signal, includes wideband and narrowband digital filters for providing wide bandwidth and narrow bandwidth baseband quadrature output signals for the widest bandwidth of operation and a narrow bandwidth of operation at a frequency within a passband. The wideband digital filtering is designed to only provide a modest amount of additional stopband attenuation with a significantly sharper transition band rolloff from passband to stopband. When this limited digital filtering is applied to the signal that has already been subjected to the analog filtering, the selectivity of the overall receiver frequency response is improved. The receiver may be used for multi-bandwidth operation by simply adding digital filtering to define any narrower passband of interest. This allows bandwidth switching to take place without any changes to the analog circuitry. Simultaneous processing of both wide and narrow modes of operation may be done in the digital signal processor (DSP) performing the digital filtering.