Conditions of High Gain in Mixers and Their Relation to the Jump Phenomenon

The Schottky barrier diode down-converter is a frequency converter that is capable of noise figures below 1 dB in the microwave range with operation at room temperature. 1 However, this converter is potentially unstable, i.e., is capable of arbitrarily high conversion gain. Evaluation of the noise performance at high gain requires a knowledge of the mechanism of instability, and of the conditions necessary and sufficient for instability. Torrey and Whitmer" derived a simple stability condition assuming weak reciprocity and also studied a particular case in detail, but their results are not applicable to the down-converter of Ref. 1. Here we derive general stability conditions, in closed form, and show that instability is intimately related to the jump phenomenon, a type of instability peculiar to periodically driven nonlinear networks. These stability conditions are applicable to any periodically driven nonlinear network (henceforth simply called a mixer) provided it is driven by a source (pump) that generates power at a single frequency . Because they are very general, these conditions can be used for a variety of purposes; for instance, suitable design criteria for harmonic generators can be determined in order to obviate the jump phenomenon and related instabilities in these devices. A brief discussion of this application is 2139