CHAPTER 4 - Multiple-Path Amplifiers

Abstract

This chapter focuses on multiple-path amplifiers. It is common for feedback amplifiers to have a significant forward transmittance through the feedback path. This results in multiple parallel (or shunt) forward paths. Shunt c–e or c–b resistance causes bilateral signal flow with a combination of feedback and multiple forward paths. Analytic techniques, adaptable to intuitive use, are based on powerful, general circuit theorems. The β transform greatly simplifies open-loop amplifier circuit analysis and makes the transresistance method possible. It can transform feedback circuits into open-loop equivalents. The β transform is half of a more general theorem, the reduction theorem. The voltage form of the transresistance method extends directly to multiple-transistor amplifier stages. The application of the voltage form of the transresistance method to bipolar junction transistor amplifiers adds the complication of rπ. Feedback analysis can be applied only if forward and feedback paths are separately identified. Then their interactions can be reduced to loading and two-port source transmittances.