EMC issues relating to the design of communicating appliances

There has been a rapid growth in the use of mobile communications with the emergence of digital radio technologies. In parallel with this PDAs (Personal Digital Assistants) are now starting to enter the market place. The development of commercial products combining both digital electronics and RF (radio frequency) circuits gives rise to some important EMC (electromagnetic compatibility) challenges. These can broadly be categorised into two areas. Does RF interference from the transmitter of the radio cause upset of the digital circuits? Will the sensitivity of a receiver be reduced if it is placed in close proximity to some digital circuitry? This paper reports explorative measurements in both these areas. Comparative measurements of susceptibility of logic gates to RF interference are presented. These results indicate that the use of HC (high speed CMOS) devices can considerably reduce susceptibility to RF interference. In addition measurements have been taken to show how receiver sensitivity can become be degraded when operating in close proximity to digital circuitry.