An analysis of IF filter effects in bandpass sampling digital demodulators

This paper presents a method for the analysis of the performance of digital demodulators which use bandpass sampling (BPS) to perform both signal spectral shifting and, noise and spurious signal suppression. The bandpass sampling technique can simplify the front-end processing of a digital receiver by eliminating RF downconversion stages. In addition, as the signal is sampled prior to downconversion to baseband, accurate conversion can be performed without the usual problems of carrier I/Q phase offsets, amplitude imbalance and carrier feedthrough. The effects of aliasing on the noise density at baseband and the effect of the BPF on the wanted signal's characteristics are analysed.