User's Manual

Table Of Contents

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.

044-05138 Rev. A 4-2 May 2003