A fast, stable quadrature phase generator for multiple-pulse NMR

Modern NMR pulse sequences usually consist of a series of radiofrequcncy (rf) pulscs having orthogonal (quadrature) phases. While there are a variety of situations where pulse accuracy is important, 1 it is especially critical for solid-state multiple-pulse NMR.2 In fact, multiple pulse sequences developed for phase measurement excced the accuracy of traditional electronic phase measuremen t techniques by an order of magnitude. 3 ; Ease of phase adjustment and stability often determine whether or not an experiment is feasible. Such quadrature phase shifting circuits are often deficient in this respect, suffering from a variety of defects, including thermal drift, interchannel crosstalk, and coarse settability. We present a design in which these weaknesses have been removed or minimized and additionally, requires only a small number of rf components.