Radio Frequency Integrated Circuit Design - Webs

Power Amplifiers
Figure 10.4 Optimal matching versus small-signal matching.
shown in Figure 10.2), optimal-power tuning produces about 1 to 3 dB of
higher power. Gain is reduced (for small P in) typically by a slightly smaller
amount.
An estimate of the optimum impedance �opt can be made by adjusting
the load so that the transistor current and voltage go through their maximum
excursion, as shown in Figure 10.5, with the output susceptance (typically
capacitive susceptance) reactively matched.
10.5 Class A, B, and C Amplifiers
Power amplifiers are grouped into classes depending on the nature of their
voltage and current waveforms. The first major classes to be considered are class
A, B, and C amplifiers. Figure 10.6 shows a basic circuit that can be used for
Figure 10.5 Current and voltage excursion of power amplifier.
353