Analysis of the Common Emitter Amplifier Taking into Account Transistor Non-Linearity

TL;DR

This paper analyzes the behavior of common emitter amplifiers considering transistor non-linearity using Early modeling, revealing how transistor parameters influence linearity and the limits of negative feedback in real-world devices.

Contribution

It introduces an analytical approach based on Early modeling to account for transistor non-linearity in common emitter amplifiers, providing new insights into device parameter effects.

Findings

Negative feedback cannot fully compensate for transistor parameter variations.

Larger Early voltage $V_a$ enhances linearity significantly.

Device parameters should be considered in amplifier design.

Abstract

The operation of a typical common emitter amplifier, including negative feedback, is studied taking into account the non-linearity characteristic of real-world transistors. This has been accomplished by employing a recently proposed Early modeling approach, which allowed the analytical equations to be obtained describing the current and voltage behavior in the adopted common emitter circuit. Average and dispersion (coefficient of variation) of the current and voltage gains can then be calculated and used to characterize the common emitter amplification while reflecting the transistor non-linearity. Several interesting results were obtained, including the fact that the negative feedback provided by the emitter resistance is not capable of completely eliminating effects of parameters differences exhibited by transistors. Importantly, transistors with larger Early voltage $V_a$ magnitudes tended to provide significantly enhanced linearity even when substantial negative feedback is used. These results motivates customized design, implementation and application approaches taking into account the parameters of the available devices.