The design of flexible receivers for communicating appliances

This paper considers several aspects relating to the design of flexible receivers in communicating appliances. It begins by describing the benefits of flexible receivers. It then goes on to explore the feasibility of developing perhaps the “ultimate goal” of a flexible receiver, comprising of an analogue to digital converter with an antenna at its input. This is done through some analysis which describes the use of sample and hold devices for frequency conversion within a radio. Through the use of a perfect multiplier a model is developed in order that the noise figure of a sample and hold device can be predicted. The results show that sample and hold devices have higher noise figures than mixers and hence their use can give rise to reduced receiver sensitivity. The analysis also demonstrates that their noise figure performance is considerably improved through the use of RF gain and filtering. This demonstrates that the ability to sample at RF can only realistically be achieved with appropriate consideration of the necessary RF gain and selectivity, and thus flexible receivers need programmable filters. Finally it concludes with a summary of the relative merits of zero IF and superheterodyne receivers