Comprehensive error analysis of ultra-wideband direct conversion receivers

In this contribution, the direct conversion receiver (DCR) has been revisited and its properties have thoroughly been studied in detail. Contrary to common practice, our main interest is focused on the investigation of DCR performance degradation in conjunction with the processing of ultra-wideband FDM-signals. To this end, all potential DCR error sources have been identified and introduced into a comprehensive error model. This model encompasses delay, gain and phase errors, DC-offsets, bidirectional crosstalk between the input ports of the down-converters and, eventually, quantisation and clipping of the analogue-to-digital interface (ADI). For all of these error sources an exact error analysis has been carried out and, in addition, compact and conveniently applicable formulae and design charts are presented for the evaluation of the isolated impact of each of the various error contributions. Furthermore, a typical error scenario taken from an ultra-wideband application in satellite communications has been used to demonstrate the overall DCR performance degradation as a result of the combination of the most important error contributions. For this application, the major degradations are caused by delay errors that are most pronounced in edge channels, DC-offsets that, however, heavily impair the channel centred about zero frequency only, and gain errors.