G3L-1929- Installation and Service Manual
Figure 4-1 Multi-Carrier Power Amplifier Functional Block Diagram
4-4.1 Preamplifier
The carrier is applied to the input port of the amplifier. This signal is fed to the preamplifier stage
where it is amplified using two stages of class A mode amplifiers. The output of the preamplifier is
then split into two paths, one to the main amplifier and one to the error amplifier.
4-4.2 Main and Error Amplifiers
The main amplifier provides approximately 14.5 dB of gain in the 1930 to 1990 MHz frequency
band (refer to table 1-2 for amplifier specifications). The main amplifier employs class AB amplifi-
cation for maximum efficiency. The error amplifier and feed forward loops are used to correct sig-
nal non-linearity’s introduced by the class AB main amplifier. The error amplifier operates in class
A mode. The RF signal from the preamp is coupled to an attenuator and phase shifter in the first
feed-forward loop where it is phase shifted by 180 degrees and amplified in the premain ampli-
fier. The output from the premain amplifier is fed to the class AB main amplifier. The signal output
from the main amplifier is sampled using a coupler, and the sample signal is combined with the
main input signal and input to the second feed-forward loop.
The error signal is attenuated, phase shifted 180 degrees, then fed to the error amplifier where it
is amplified to a level identical to the sample output from the main amplifier. The output from the
error amplifier is then coupled back and added to the output from the main amplifier. The control
loops continuously make adjustments to cancel out any distortion in the final output signals.
Copyright Powerwave Technologies, Inc., May 2003. All rights reserved
044-05138 Rev. A
4-2
May 2003
