Radio Frequency Integrated Circuit Design - Webs

Power Amplifiers
The efficiency is plotted in Figure 10.11.
The actual output power for an output peak voltage of Vop can be found
as a function of � :
359
Pout = Vop ICC (2� − sin 2� ) (10.14)
4�
noting that to get maximum power, the load resistance has to be adjusted so
that the maximum voltage vo,max is approximately 2VCC and the minimum
voltage vo,min is approximately zero, thus V op is equal to V CC .
The above equation will be more convenient to plot if we eliminate ICC .
Recall that ICC is a measure of the peak current, not with respect to zero, but
with respect to the center of the sine wave where the center for class C is less
than zero, as shown in Figure 10.12.
Figure 10.11 Maximum efficiency versus conduction angle.
Figure 10.12 Time-domain waveforms for various conduction angles.