Technical Manual

A-10 ATLAS 4500 Multimode Station Technical Manual July 2016
760-870 MHz Power Amplifier Appendix A - 700/800 MHz Circuit Descriptions
A.3.2 Schematic Description
A.3.2.1 General
The RF input is ~ 12 dBm into CN1. The PA provides 1-100 W output across 760 –
870 MHz band at the main N type connector. The Main supply is 48V at < 10A at
CN3. The secondary supply is 24 V at 450 ma at CN2, and 5 V at 10 ma at CN2.
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.
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.