Frequency Generating Section - Motorola MTM700 Detailed Service Manual

THEORY OF OPERATION (400 MHz)
The analog modulation signal is passed on to the LNODCT where it is up-converted to the transmit-
ter operating frequency. The modulated RF output signal from the LNODCT is converted from differ-
ential to single-ended by a balun, and passed to the attenuator, pre-driver IC, driver transistor,
power amplifier transistor, directional coupler, and isolator (depends on radio model), from where it
is routed to the antenna via the antenna switch and harmonic filter. An RF feedback signal is taken
from the directional coupler and fed back to the LNODCT for transmitter power control and lineariza-
tion.

Frequency Generating Section

The frequency generating section comprises the following components
(see figure below):
• 16.8 MHz TCXO Reference Oscillator.
• Main Synthesizer - consists of the Main Voltage Controlled Oscillator (VCO) and Low Voltage
Fractional-N (LVFRACN) integrated circuit PLL. 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.
16.8 MHz Ref. to
Controller
16.8 MHz Ref.
to IF Digitizing
Subsystem
Buffer
16.8 MHz
TCXO
MTM700 Mobile Radio / Detailed Service Manual
Frequency
Translation
PLL
(ESCORT)
Buffer
Reference
Divider
Detector
Prescaler
Warp DAC
LVFRACN PLL
Figure 4 Frequency Generating - Block Diagram
Loop
TX
Filter
VCO
Loop
Phase
Filter
Buffer
Tx Injection
to LNODCT
Buffer
Main
Buffer
VCO
VCO BIC
4.1 - 7
To Rx
st
1 LO