Fluctuation noise in single and multi-collector vacuum tubes in the space-charge-limited condition
Kyriacou, Robert J.
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This paper presents an exposition of the significant theories of fluctuation noise for vacuum tubes in the space-charge-limited condition. The theories presented are for low frequencies, that is, frequencies where transit time effects are not-significant. The importance of noise in the general communications problem is discussed in Part I. In Part II the historical development of fluctuation noise theories is presented commencing with work of W. Schottky on the temperature-limited diode. The practical importance of the noise phenomenon to the tube manufacturers is pointed out. The historical development of thermionic emission theory is briefly traced beginning with C. Child's famous three-halves power law. The basic problem in the determination of space-charge conditions is next discussed. This is followed by excerpts from fluctuation noise investigations in 1925 by A. Hull and N. Williams. The progress of noise investigations from 1931 - 1940 is traced. Special reference is made to the work of B. J. Thompson, D. 0. Williams, and W. A. Harris in the development of practical engineering formulae. The achievements of the Radiation Laboratory of M. I. T. from 1941 - 1950 are noted. Part III presents a derivation of the original Shottky equation for temperature limited diodes...[TRUNCATED]...This equation is derived by use of Fourier series and probability theory. Part IV considers the space-charge picture in detail. The mechanism of thermionic emission is discussed in terms of the theory of work function and Richardson's equations. Reasons for preferring the T^2 version of Richardson's equations are given. The nature of the temperature - limited condition is next considered and is followed by a description of the space-charge-limited case. The reasons for noise reduction in space-charge-limited diodes is discussed by way of reference to the experimental work of A. Hull: and N. Williams. The opinions of other investigators on the cause of noise reduction are also noted. Part V discusses the various experimental confirmations of the Maxwell distribution law. Statistical mechanics is used to show how the Fermi-Dirac distribution law reduces to the Maxwell distribution law at emission temperatures. The T. C. Fry method of analysis of space-charge-potential distribution in diodes is next presented. This analysis takes into account the initial Maxwell velocity distribution of emitted electrons and enables a determination of space-charge-potential for all diode space-charge conditions. A fluctuation noise theory for multi-element tubes (tetrodes, pentodes, etc.) is presented in Part VI. The D. 0. North theory of current division is given. This is a comprehensive and quantitative theory showing how excess noise is caused by a division of tube current among the collector electrodes. Several conclusions resulting from this theory are given.
Thesis (M.A.)--Boston University
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