OSCILLATION AND SWITCHING IN TUNNEL DIODES

Abstract

The studycovers a wide range of topics in the field of negative resistances. Generalized stability criteria based on the index principle, of which Nyquist's criterion is a special case which uses the driving point impedance (or admittance) functions (calculated or measured) have been developed. The criteria and an examination into the methods of generating negative resistance justify the two different types of simplified small signal equivalent circuits for the current and voltage controlled negative resistances. The construction of a current controlled negative resistance analog is described. The principle of duality and the availability of both current and voltage controlled analogs make a unified approach to the study of negative resistance circuits a possibility. A good prediction for the limit cycle (steady state frequency and amplitude) for a simple tunnel diode oscillator has been obtained by using the Kryloff and Bogoliuboff tech­nique. The oscillation hysterisis has also been discussed. Well-known methods of nonlinear analysis such as piece­ wise linearization, graphical, isocline, analogue and digital computer techniques have been adopted for solving nonlinear differential equations met with in tunnel diode circuits. The fundamental aspect of switching in all multi-stable systems, namely the separatrix which is the boundary between the various domains has been studied for the case of switching of a tunnel diode when the lead inductance is not negligible. The final value problem of determining the separatrix has been converted to an initial value problem by making time go backwards. The plot of separatrices for both linear and nonlinear loads obtained on a digital computer has provided insight into the role of inductance in minimizing trigger requirements and in the operation of some elegant tunnel diode switching circuits. In general, the inductance bends the separatrix (which is a vertical line through the cross­over point for zero lead inductance) towards the stable points, thereby reducing trigger (current or voltage amplitude) requirements.