Motorola MTM700, Detailed Service Manual

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THEORY OF OPERATION (800 MHz) MTM700 Mobile Radio / Detailed Service Manual 4.2 - 5
Frequency Generating Section
The frequency generating section comprises the following components:
• Reference Oscillator - TCXO
• Main Synthesizer - consists of the Main Voltage Controlled Oscillator (VCO) and Low Voltage
Fractional-N integrated circuit (LVFRACN). In receive mode, the main synthesizer provides
the local oscillator injection to the receiver first mixer. In transmit mode, this synthesizer
provides the frequency reference for the transmit frequency translation loop.
• Transmit frequency translation loop. Consists of the transmit Voltage Controlled Oscillator
(VCO) and ESCORT Near Unity Divider (NUD) Phase Locked Loop IC.
Block Diagrams Descriptions
The block diagrams descriptions cover Receiver Path, Transmitter Path, Frequency Generation
Section, and Controller Section.
Receiver Path
The received signal (see figure below) from the antenna is directed by the Antenna Switch to the
Front Pre-selector Filter.
Figure 2 Receive Path Block Diagram
Antenna
Switch
From Tx PA
DSP (Part of
Controller)
2
nd
Mixer
1
st
LO From
FGU
LNA
2
nd
LO
ADC
Loop
Filter
Sample
Clock
VCO
Loop
Filter
2
nd
LO
PLL
Variable
Gain
Amplifier
Formatting
SSI
(BBP)
IF Digitizing
Subsystem
16.8 MHz
Reference
from FGU
Sample
Clock
PLL
Tx
Rx
AGC_2
Attenuator &
Buffer
Decimation
Filter
Image
Filter
Mixer
73.35 MHz
First IF Filter
IF
Amplifier
Harmonic
Filter
LNA Pre-selector
AGC_1
Attenuator
AGC_0
Attenuator
CODEC
AUDIO
PA