Motorola Professional GP640 Service Information - Page 9

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Motorola Professional GP640 Service Information
1.0

Introduction

This Chapter provides a detailed theory of operation for the UHF2 circuits in the radio. For details of
the theory of operation and trouble shooting for the the associated Controller circuits refer to the
Controller Section of this manual.
2.0

UHF2 Transmitter

( Refer to Figure 2-1 and the UHF Transmitter schematic diagram )
The UHF2 transmitter consists of the following basic circuits:
1.
Power ampliÞer (PA).
2.
Antenna switch/harmonic Þlter.
3.
Antenna matching network.
4.
Power Control Integrated Circuit (PCIC).
From
VCO
2.1
Power AmpliÞer
The power ampliÞer (PA) consists of two principle devices:
1.
LDMOS PA driver IC, U101.
2.
LDMOS PA Þnal stage, Q110.
The LDMOS driver IC provides 2-stage ampliÞcation using a supply voltage of 7.3V. The ampliÞer is
capable of supplying an output power of 0.3W (pins 6 and 7) with an input signal of 2mW at 3dBm
(pin16). The current drain is typically 160mA while operating in the frequency range of 450-527MHz.
P C I C
Vcontrol
Power
Amplifier
PA
Driver
Figure 2-1 UHF2 Transmitter Block Diagram.

THEORY OF OPERATION

Vcontrol
Antenna Switch/
PA Final
S t a g e
Harmonic Filter
Chapter 2
Antenna
Matching
Network