A CAD-oriented method for optimal biasing of amplifiers

In the automated design of amplifier circuits, the biasing constitutes a serious obstacle that is usually overcome by resorting to the application of heuristics or thumb rules based on the experience of the designer. In fact, biasing can be regarded as the procedure that results in smartly placed bias sources of the amplifier while keeping its small-signal behaviour intact. This paper introduces a CAD methodology that uses the circuit topology on its full extent in combination with some design-driven criteria in order to determine the optimal placement of the bias sources. The method is based on the concepts of current-stimuli and voltage-stimuli graphs. A dynamic deformation of the trees and co-trees of both graphs is achieved with the aim of obtaining the appropriate placement of the bias sources.