Negative Feedback, Linearity and Parameter Invariance in Linear Electronics

TL;DR

This paper systematically investigates how negative feedback can improve device invariance and linearity in bipolar transistors, revealing partial success and highlighting the importance of considering device properties in linear circuit design.

Contribution

It provides a comprehensive analysis combining theoretical and experimental methods to quantify negative feedback effects on transistor variability and linearity, with new insights into device grouping and feedback efficiency.

Findings

Transistor types have well-defined, segregated characteristics.

Negative feedback promotes partial uniformization of device properties.

Linearization effects depend on the original device transfer functions.

Abstract

Negative feedback is a powerful approach capable of improving several aspects of a system. In linear electronics, it has been critical for allowing invariance to device properties. Negative feedback is also known to enhance linearity in amplification, which is one of the most important foundations of linear electronics. At the same time, thousands of transistors types have been made available, suggesting that these devices, in addition to their known variability of parameters, have distinguishing properties. The current work reports a systematic approach to quantifying the potential of negative feedback, with respect to bipolar transistors, as a means to providing device invariance and linearity. Several methods, including concepts from multivariate statistics and complex systems, are applied at the theoretical as well as experimental levels, and a number of interesting results are obtained and discussed. For instance, it has been verified that the transistors types indeed have well-defined characteristics which clearly segregate them into groups. The addition of feedback at moderate and intense levels promoted uniformization of the properties of these transistors when used in a class A common emitter configuration. However, such effect occurred with different efficiency regarding the considered device features, and even intense feedback was unable to completely eliminate device dependence. This indicates that it would be interesting to consider the device properties in linear design even when negative feedback is applied. We also verified that the linearization induced in the considered experiments is relatively modest, with effects that depend on type of transfer function of the original devices.