Hall Effect Stroboscope and Noise Discriminator

Abstract

Construction and performance criteria of a stroboscope, based upon the pulsed operation of Hall effect generators, are presented with special reference to the properties of evaporated thin films of indium antimonide. A high-frequency periodic magnetic field of arbitrary waveshape is converted by the stroboscope into a low-frequency replica of the input signal. This is accomplished by sampling the magnetic field by means of synchronized narrow rectangular current pulses applied to the Hall plate. These current pulses are phase modulated allowing the magnetic field to be scanned point by point thus producing an output voltage which, after integration, is a lower frequency synthesis of the input signal. The advantages of the stroboscope include a linearity between input and output signals to better than 1% and good frequency response between 100 cps and 5 Mc. Hall effect stroboscopes built in this manner also have superior properties as noise discriminators. They will not respond to ambient magnetic fields, except those of the same frequency as the input signal or its harmonics. The advantages of pulsed operation of thin film Hall effect devices in semiconductors with charge carriers having a short relaxation time are shown to be greatly improved sensitivities to small magnetic fields because of the greater peak current densities applicable to the film without any attendant Joule heating.