Technical Manual

760-870 MHz Power Amplifier
Appendix A - 700/800 MHz Circuit Descriptions
A-
11
ATLAS 4500 Multimode Station Technical Manual July 2021
NOTE
The Controller uses the PA calibration data stored in IC11 during PA calibration, FWD VOLTS
from the power detector, TX frequency and O/P power settings set from the DSP to control the
attenuator values dynamically.
A.3.2.2 Attenuator
CN1 at ~12 dBm enters attenuator IC1. This provides attenuation steps of 0.25 dB
from a 2 dB minimum. This is used by the Controller for power control through
CN2 pins 3, 4, 5 lines.
A.3.2.3 Driver Module
The attenuator IC feeds an amplifier module IC2 to provide drive for the main PA
amp.
This module is a high linearity low intermodulation 75-Ω power driver with ~24 dB
gain, 28 dBm RF power. It operates at 24 V at 450 ma.
A.3.2.4 Output Power Amp
The PA output power amp stage uses a high performance power FET in a Gemini
package. This is mounted on a copper heat spreader plate, on a fan-cooled
aluminium heat sink.
The input matching uses a 90° section 17-Ω transmission line balun. Then, a
balanced matching section to a ~ 0.5-Ω Zin FET.
Input series resistors and a parallel resistor are used to prevent instability.
The output match from ~ 6 Ω Zout consists of a 2-section match, then to a 90°
section 17-Ω transmission line balun to give 50-Ω feed.