Digital Sampling Strategies that Discriminate Against Mains Interference (Noise). A Tutorial Review

Abstract

Mains interference is a severe problem in microelectrode measurements. Its fundamental frequency (50 Hz in Australia and the U.K., 60 Hz in the U.S.A.) lies in the centre of the bandwidth in which microelectrode measurements are made (10^–3 Hz to 10⁶ Hz), and therefore it is very difficult to remove once it has contaminated a signal. In this tutorial review I briefly sketch the background to this problem, and then describe in detail a digital sampling strategy that actually discriminates against mains interference even when the interference is harmonically distorted. The recommended strategy, which Rex Deutscher and I invented several years ago, is particularly valuable in cases where digital sampling rates are under software control, and commercial mains-rejecting hardware is not available. We call the strategy “magic sampling”.