By Louis E. Frenzel, Electronic Design – April 2009
Software-defined radio (SDR) replaces traditional radio circuitry like mixers, filters, and demodulators with software that runs on a DSP or with FPGAs. The secret to its success is its ability to sample the radio signal quickly enough so the DSP can do its job. However, the upper sampling speed of analog-to-digital converters (ADCs) has inhibited its capabilities. Modern chips can easily sample in the hundreds of megahertz and lower gigahertz ranges, but there are still limitations in dynamic range and resolution. That’s the reason why most SDRs are implemented at the intermediate frequency (IF) level rather than directly at RF. … Hypres Inc. has been working to solve that problem, though, with its digital RF direct conversion to baseband technology. Hypres has applied its expertise in superconductors to create ICs that operate under cryogenic conditions to produce exceptional switching speeds (see the figure). When cooled to temperatures near absolute zero (zero degrees Kelvin or about –453°F/–269°C), superconductors lose all electrical resistance.