A Treatment of Non-Linear Devices Based upon the Theory of Related Linear Functions

Because of the mathematical difficulties involved in the treatment of large-signal detectors, experimental methods for obtaining design data were early adopted. The procedure has been to replace the detector by a ``model'' described by a rectification or transrectification diagram. The ``model'' for a large-signal detector is developed from practical measurement results. Formulae and results may be extracted from the ``model'' if the existing analogy with the plate-current vs. plate-voltage diagram for a vacuum tube is made use of. This fundamental procedure may be extended to other non-linear devices, and in particular to frequency converters. It is shown in the following that a general theory can be developed, of which the vacuum-tube amplifier, the large-signal detector, the frequency converter and other devices are applications. A double-inpout superheterodyne mixer with straight input characteristics is discussed, and it is shown how the applied general theory predicts the necessity for non-linearity. The general theory is then used for the development of a substituting ``model,'' from which important information on the behavior of a superheterodyne converter can be secured.