The Gain Game: Using the Four Principal Amplifier Gain Metrics

In the ongoing quest to improve energy efficiency for power amplifiers (PAs), it is necessary to operate the amplifier transistors in both the cutoff and nonlinear compression operating regions [1], [2]. In these operation modes, the usual measures of amplifier gain can no longer be used indiscriminately [3]. Earlier work with the amplifier voltage transfer function shows how the slope and ratiometric gains of any amplifier diverge as nonlinear amplifier operation increases [4]. Here, the extended gain metrics, which also include the power transfer function [5], bring the total number of important gain metrics up to four. While many of these points may seem elementary, it is well documented that concepts regarding gain are actually not clearly understood. It is worthwhile to clarify these important differences because designs using intentional amplifier compression are becoming more common. We can then evaluate their relative effectiveness in support of design tasks such as PA linearizers.