Irreversible thermodynamics and thermal noise of non-linear networks

The conventional treatment of thermal noise is based on Nyquist's theorem. This theorem has only been derived for linear, reciprocal (we define "reciprocal networks" as networks that are built of reciprocal network elements) networks. In this paper a description of thermal noise in reciprocal non-linear RLC networks is presented. This description is derived from first principles, i.e. from a direct application of non-equilibrium thermodynamics (irreversible thermodynamics) to electrical networks. As an example, the class of "complete" non-linear networks is considered. Using the idea of equivalent n-ports, the theory's extension to certain classes of transistor circuits should be possible.