Optimum Design of Sensitive Tunnel Diode Discriminators

Abstract

A new and useful theory was developed to characterize switching properties of the tunnel diode. Expressions for time delay and time variance for small signals in the presence of amplitude noise were developed for the tunnel diode in the discriminator mode. The expression for time variance is used to determine the parameters of the tunnel diode, and the tunnel diode bias condition to obtain the optimum time resolution for a specified signal and noise. The minimum charge necessary to switch the tunnel diode is calculated for a given signal current pulse width and tunnel diode bias condition. The expressions characterizing the properties of the tunnel diode were developed after the author discovered experimentally that the positive resistance region of the device could be represented very accurately by a sine function in voltage. Since this region of the characteristic curve is responsible for the significant delay and time variance, it is sufficient to describe these properties of the tunnel diode discriminator. The usual equivalent circuit is used to represent the tunnel diode. The second order nonlinear differential equation which is necessary to describe the equivalent circuit is simplified by excluding terms which were insignificant for this particular mode of operation. The simplified differential equation is solved to determine the time for the tunnel diode to switch from its stable bias point to the negative resistance region. This switching time, or delay time, is then used to calculate the time variance.