Correlation Measurements of Signals and Noise

Abstract

It has recently been shown that the characteristic of an electronic device fluctuates, and that this may possibly account for the increase in noise level obtained when a.c. signals are applied to semiconductor devices. The aim of the present research is to investigate further the effect of these fluctuations in characteristic on the noise of electronic devices, and to determine how they will affect any signals being transmitted. The investigation was carried out in two parts. In the first part a theoretical and experimental investigation of the shot noise of thermionic valves was made. As a result of this investigation it was concluded that a theory of space charge smoothing based on the hypothesis of a fluctuating characteristic gives a better estimate of the space charge smoothing factor than do other, more widely accepted, theories. The second part is concerned with the transmission of signals through amplifiers. Both autocorrelation and crosscorrelation techniques were used to determine how these signals are affected by the fluctuations in characteristic. The results so obtained are shown to conflict with the results of an earlier experimentor, Hathaway, but not to conflict with those of another, Bozic, and indicate that signals are almost unaffected by fluctuations in the characteristic of the amplifier through which they are transmitted.