A Sampling Linear Detector for Accurate rf Pulse Amplitude Measurement

Abstract

A sampling linear detector is described which has been developed for measuring one‐shot free precession amplitudes at 1.5 MHz in a pulsed NMR experiment. A 10⁻³ accuracy is achieved over a 30 dB dynamic range with a 60 μsec gate aperture time. The rectifying circuit is made up of two low threshold hot carrier diodes placed in the feedback loop of a fast operational amplifier. A bias voltage technique is employed for further linearization. Commercial integrated circuits and operational amplifiers are used throughout and make layout and wiring noncritical. Checking and calibration prodedures, as well as circuit operation, are carefully analyzed.