Power Gain and Stability of Multistage Narrow-Band Amplifiers Employing Nonunilateral Electron Devices

Abstract

This paper gives an analysis of the transducer power gain and stability of a multistage, narrow-band amplifier employing nonunilateral electron devices. The amplifier is assumed to consist of n identical stages with the input and output terminations. The individual amplifier stage consists of a general active two-port device, such as the transistor, characterized by its four short-circuit admittance parameters, plus a two-terminal interstage network and an ideal coupling transformer. Both the individual amplifier stage and the over-all cascade of n amplifier stages, considered as a composite active two-port, are also characterized by their short-circuit admittance (Y) parameters. Relations between these Y parameters of the individual amplifier stage and the Y parameters of the over-all iterative amplifier have been derived. The transducer gain of the amplifier as a function of the interstage and the terminating network parameters has been studied. The transducer gain is optimized with respect to the external passive terminations and is expressed in terms of a design parameter \gamma , which is directly related to the terminating conductances of the amplifier. It is shown that for an amplifier employing inherently stable active devices, there is a value of \gamma which gives maximum transducer power gain; for an amplifier employing potentially unstable active devices, the optimum transducer power gain of the amplifier will, in general, be a monotonically decreasing function of \gamma . In any case any prescribed value of \gamma determines the maximum gain obtainable from the amplifier. The amplifier's margin toward instability is prescribed through prescribing a number \rho_{l} . For \rho_{l} greater than unity, the amplifier will be stable. Control of \rho_{l} is effected through appropriate choice of the design parameter \gamma . A relation relating \rho_{l} , and \gamma has been derived. Some fundamental considerations in the design of multistage, narrow-band amplifiers employing general active two-port devices are given. Results of experimental two-and three-stage transistor amplifiers are presented which show excellent agreement between the theoretical and the experimental results.