Theory of the Esaki diode frequency converter

Abstract

The small-signal conversion properties of an Esaki (tunnel) diode are represented by a simple two-port conductance matrix whose elements are certain coefficients of the periodic time-dependent diode conductance produced by the local oscillator (pump). Because of the negative slope in the diode I–V characteristic, arbitrarily high conversion gain is possible when certain conditions are satisfied by these coefficients. In terms of these coefficients and other diode parameters, expressions are derived for such useful converter properties as the load conditions necessary for circuit stability, the minimum noise figure, the maximum gain-bandwidth product, the necessary conditions for a positive mixer conductance at the radio frequency (r.f.) and intermediate frequency (i.f.) ports, and the pump loading necessary for self-excitation. It is shown that under proper conditions partial noise cancellation can occur because of correlation effects arising from the nonstationarity of the shot-noise process in the pumped diode. Most of the theoretical results are illustrated by the data obtained from a detailed numerical Fourier analysis applied to an actual high-frequency Esaki diode characteristic. These calculations show that the lowest noise figure and the highest gain-bandwidth product are obtained when the diode is biased in its negative conductance region.