Eliminating Broadband Distortion in Transistor Amplifiers

System studies have indicated that very broad band (greater than 20 mHz) AM coaxial cable systems will be modulation-limited. Intensive investigations to understand and characterize the inherent modulation properties of devices and repeater circuits have been called for. We made one such study directed toward understanding the basic distortion mechanisms in transistors. 315 316 T H E BELL SYSTEM TECHNICAL JOURNAL, MARCH 1968 The history of transistor distortion literature can be characterized as an erosion process in which highly restricted parts of the total problem are attacked leaving fresh complexities exposed for future work. In early work by Akgun and Strutt, the analysis is restricted to nonlinearities in the emitter resistance assuming an ac short at the input and output.1 Observed nulls in second and third order distortion do not correlate with the theoiy, which does, however, include frequency effects. Using many of the same assumptions, Mallinckrodt and Gardner extended this earlier work to account for a third order null at low frequencies when the nonlinear emitter resistance is dominant.2 More recently Riva, Beneteau, and Dalla Volta considered all important sources of distortion by breaking the problem into three distinct operating regions with expressions for minimizing second order distortion in each. 3 They do not treat of third order minimization, and they use a dc model. Reynolds analyzes third order minimization at particular nonzero frequencies for dominance of the emitter resistance nonlinearity.