Radio receivers for digital cellular systems must respect tight constraints in terms of selectivity and dynamic range.Delta-sigma analog-to-digital converters offer a response to the last problem thanks to their high resolution. On the other hand, selectivity is often achieved by filtering the received signal at an intermediate frequency (IF). Limitations of A/D converters impose usually an extra IF conversion of the signal to a lower frequency before being able to properly digitize it.We propose a new delta-sigma converter operating directly on the IF signal allowing the design of simple receivers offering both a high resolution and a good selectivity. Undersampling the IF signal allows moreover to reduce the load of the digital section of the receiver.

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SUIbf MARYHigh-performance bandpass sigma-delta modulators find applications in digital mobile radio for accurate analogue-todigital conversion in receivers.An approach based on the positioning of the poles and zeros is proposed for the digital design of the high-order loop filters which are required. Inverse notch filter sections are cascaded in a first step and then poles and zeros are moved to meet the performance objectives and achieve system stability.A distinct feature of the analysis and design technique presented is that it takes stability into account explicitly. Examples illustrate the practicality of the method as well LS the level of performance which can be achieved in theory. The integrated circuit realization still has to be investigated to confirm the potential of the proposed design approach.