Circuit synthesis based on a prescribed Lagrangian

Abstract

On the basis of a prescribed quadratic Lagrangian, an algorithm of synthesis for an electric circuit is suggested here. That is, the circuit evolution equations are equivalent to the relevant Euler–Lagrange equations. The proposed synthesis is a systematic approach that allows one to realize any finite-dimensional physical system described by a quadratic Lagrangian in a lossless electric circuit so that their evolution equations are equivalent. The synthesized circuit is composed of (i) capacitors and inductors of positive or negative values for the respective capacitances and inductances, and (ii) gyrators. The circuit topological design is based on the set of L C LC fundamental loops (f-loops) that are coupled by G L C GLC -links each of which is a serially connected gyrator, capacitor, or inductor. The set of independent variables of the underlying Lagrangian is identified with f-loop charges defined as the time integrals of the corresponding currents. The EL equations for all f-loops account for the Kirchhoff voltage law whereas the Kirchhoff current law is fulfilled naturally as a consequence of the setup of the coupled f-loops and the corresponding charges and currents. In particular, the proposed synthesis provides for efficient implementation of the desired spectral properties in an electric circuit. The synthesis provides also a way to realize arbitrary mutual capacitances and inductances through elementary capacitors and inductors of positive or negative respective capacitances and inductances.