Chapter 2 Theory Of Operation; Lowband Transmitter; Power Amplifier (Pa) - Motorola Professional GP340 Service Manual

1.0 Introduction
This chapter provides a detailed theory of operation for the radio RF circuits. Refer to the relevant
section of this manual for details of the operation of the Controller Circuits.
2.0

Lowband Transmitter

( Refer to Figure 2-1 and the Lowband Transmitter schematic diagram )
The Lowband transmitter consists of the following basic circuits :
■

Power amplifier (PA).

■
Antenna switch/harmonic filter.
■
Antenna matching network.
■
Power Control Integrated Circuit (PCIC).
2.1 Power Amplifier (PA)
The power amplifier (PA) consists of two LDMOS devices:
1. PA driver IC, U101.
2. PA final stage, Q100.
The LDMOS driver (U101) provides 2-stage amplification using a supply voltage of 7.3V. The
amplifier is capable of supplying an output power of 0.3W (pins 6 and 7) with an input signal of 2mW
at (pin16). The current drain is typically 120mA while operating in the frequency range of
29.7 - 50 MHz. The power output of this stage is varied by the power control loop which controls the
voltage on pin 1.
SPI Bus
P C I C
V Control
Power Amplifier (PA)
PA Driver
Figure 2-1 Lowband Transmitter Block Diagram.
THEORY OF OPERATION
Antenna switch bias
Gate bias
Antenna Switch/
PA Final
Harmonic Filter
Stage
Chapter 2
Antenna
Matching
Network