4.1 - 6 THEORY OF OPERATION (TRANSCEIVER)
• Formats the I and Q data streams into a serial bit stream, which is sent for further processing
to the Digital Signal Processor (DSP) (part of the micro controller) over the Synchronous
Serial Interface (SSI) data link.
The DSP performs the following functions:
• Base band filtering,
• Synchronisation
• Demodulation
• Forward Error Correction (FEC)
• other correction algorithms for overcoming channel errors, and
• the decoder procedure for digital speech data decompression.
Transmitter Path
When the terminal is transmitting (see figure below), microphone audio is sent to the CODEC, which
performs analog-to-digital conversion and routes the digital signal to the DSP. The DSP performs
the following functions:
•coding,
• error correction, and
• generation of the baseband modulation waveform.
From the DSP, baseband digital ‘I’ and ‘Q’ modulation waveform samples are sent to the ADDAG IC,
where the digital data is converted into baseband analog ‘I’ and ‘Q’ waveforms and filtered.
Figure 4.1-3 Transmit Path Block Diagram
The analog modulation signal is passed on to the JAVELIN where it is up-converted to the
transmitter operating frequency. The modulated RF output signal from the JAVELIN is converted
from differential 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 terminal 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 JAVELIN for transmitter power
control and linearization.
ADDAG
JAVELIN
Balun and
Attenuator
DSP
CODEC
Attenuator
Coupler
Antenna
Switch
To
Receiver
Harmonic
Filter
Tx
Rx
Isolator
(Depends
on Model)
RF Feedback
Pre-driver
PA
Mic
Driver
Buffer
Tx LO
Injection
from FGU
Differential
Signal for
Up- and Down
Converter
Balun
6866539D31.book Page 6 Tuesday, March 20, 2007 6:32 PM
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