High Speed, Bandpass Sampling of Digital Communications Waveforms

摘要

The purpose of this thesis is to investigate and analyze bandpass sampling techniques. Bandpass sampling theory is shown to be an extension of the Shannon low-pass sampling theory. Five bandpass sampling techniques are investigated; direct sampling (also called first-order sampling), pth-order sampling (in particular second-order sampling where p=2), conventional quadrature sampling, quadrature sampling, and complex sampling (also called Hilbert transform sampling). Direct sampling is a single channel approach to bandpass sampling while the other approaches require two channels. The two channel techniques offer a sampling rate reduction of up to one half over direct sampling, but there are trade-offs to consider when choosing a two channel technique. It is shown that the effects of random phase error can render the conventional quadrature sampling approach useless. Timing is critical with quadrature sampling. Reconstruction error, due to hardware timing errors, is shown to be directly proportional to the center frequency and is a function of the bandwidth of the signal.