Classes and properties of multiloop negative-feedback amplifiers

A classification of negative-feedback amplifiers with up to the maximum of four overall feedback loops is presented, forming the complete set of two-port amplifier types with fundamentally different transfer properties. Nonenergic feedback techniques are Introduced, making use of Ideal gyrators and transformers in the feedback networks, thus enabling unlike other wide-band feedback techniques, the maintenance of the signal-to-noise ratio and the signal-handling capablity and power efficiency of the active part of the amplifiers. Theoretically, input and output Impedances can be obtained that are either zero or infinite, or linear and accurately known. In addition, a class of practical amplifier configurations Is presented, where the gyrators are replaced by transformers and Impedances. Nonenergicness Is lost as a consequence, but interesting transformer-feedback configurations are obtained, some of which are new. They are especially suitable for characteristic Impedance matching with very low noise figures and small losses of output power.