Frequency Generating Section - Motorola MTM800 User Manual

THEORY OF OPERATION (TRANSCEIVER)

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
The reference oscillator –TCXO is a temperature compensated crystal oscillator producing an
accurate and stable 16.8 MHz master clock, from which all other clocks in the terminal are derived.
It provides the reference frequency for the following components:
• the main frequency synthesizer,
• the IF Digitizing Subsystem,
• the ADDAG, and
• the micro controller
Its operating frequency is fine tuned by means of a warp voltage signal which is controlled by the
controller and generated by the LVFRACN IC
Frequency
Translation
PLL
(ESCORT)
Buffer
Reference
Divider
Detector
Prescaler
Warp DAC
LVFRACN PLL
Figure 4.1-4 Frequency Generating - Block Diagram
Loop
Filter
VCO
Loop
Phase
Filter
TX
Buffer
Buffer
Main
Buffer
VCO
VCO BIC
4.1 - 7
Tx Injection
to JAVELIN
To Rx
st
1 LO