Direct down conversion receivers and intermodulation balance

Direct down converting receiver architecture is reviewed. The impetus for moving towards this architecture is driven by cost, however it does have some design drawbacks. Volterra analysis is used to show how coefficients often neglected in heterodyne radios can play a significant part in the overall performance of a radio, although careful review of any spurious tones should be analysed before switching to this design topology. Measurements are taken with different devices from two process technologies - Gallium Arsenide (GaAs) and Silicon Germanium (SiGe) with differing results. Overall the GaAs devices are more linear, however the second order performance is significantly better with SiGe and it is thought that this could be attributed to balance.