Software Configurable Receivers

Heterodyne and Direct Conversion Homodyne receivers have been studied for a long time. It can be shown that the classical advantages as high sensitivity and high selectivity can not be transferred easiliy to the requirements arising from software configurable systems. Already for a dual-frequency receiver the Direct Conversion approach has a clear cost advantage. However, these types of receivers require significant efforts for the correction of static and dynamic errors which in practical cases very often reduce sensitivity and flexibility. Sixport non-mixing direct conversion architectures may be a multiple alternative to the aformentioned structures: The rectifying process can be very broadband and therefore multi-band capable and the front-end provides a low cost potential. Re-configurable receivers with direct RF sampling can provide multimode, multirate and multiband functions in a single hardware platform. The current bottleneck in the direct digitizing receivers is the analog to digital converter. With currently available analog to digital converters bandpass limited sub-sampling in the carrier frequency range of up to 1 GHz is possible. The concept of bandpass limited subsampling became recently a very suited architecture approach as the increasing cut-off frequency and speed of semiconductor technologies can be traded against resolution in this concept. Direct digital receivers for broadcast standards become feasible. At still higher frequencies new analog to digital converter architectures have to be investigated. The specific design of the hardware architecture becomes more and more a compromise between the specifications of the services to be handled by the receiver and the availability of components.