Direct downconversion of multiple RF signals using bandpass sampling

The center idea behind the software radio architecture is to place analog-to-digital and digital-to-analog converters as near the antenna as possible, leaving the implementation of the most radio functionality to a programmable micro or signal processor. One way to accomplish this in a radio receiver front end is by direct downconverting the desired radio frequency (RF) signal to a target intermediate frequency (IF) using bandpass sampling. Although the bandpass sampling theory for a single RF signal is well developed, its counterpart for two or more RF signals is relatively immature. For direct downconverting multiple distinct RF signals, determining valid bandpass sampling frequencies using the conventional approach could be a computationally exhaustive process. In this paper, we propose an efficient method to find the ranges of valid bandpass sampling frequency for direct downconverting multiple distinct RF signals. Simple formulas for the ranges of valid bandpass sampling frequency in terms of bandwidths and frequency locations of the RF signals are derived. The result can be used to efficiently choose an appropriate bandpass sampling frequency for multiple RF signals.