Motorola ASTRO XTS 5000 - Analog Mode of Operation; Figure 3-2. Receiver Block Diagram

July 16, 2004 6881094C28-D
3-2 Basic Theory of Operation: Analog Mode of Operation
3.2 Analog Mode of Operation
This section provides an overview of the analog mode receive and transmit theory of operation.
3.2.1 Receiving
When the radio is receiving (See Figure 3-2), the signal comes from the antenna connector to the
Transceiver board, passing through the antenna switch and the receiver front end. The signal is then
filtered, amplified, and mixed with the first local-oscillator signal, generated by the voltage-controlled
oscillator (VCO).
Figure 3-2. Receiver Block Diagram
The resulting intermediate frequency (IF) signal is fed to the IF circuitry, where it is again filtered and
passed to the Abacus III digital back-end IC. In the digital back-end IC, the IF signal is mixed with the
second local oscillator to create the second IF at 2.25 MHz. In the back-end IC, a bandpass, sigma-
delta, analog-to-digital converter then decodes the second IF signal, and outputs, on the radio’s
serial synchronous interface (SSI) bus, digital audio to the VOCON board.
On the VOCON board, the dual-core processor’s digital-signal processor (DSP) digitally filters the
PCM audio. The DSP decodes the information in the signal and identifies the appropriate destination
for it.
• For a voice signal, the DSP will route the digital voice data to the CODEC inside the audio and
power supply support IC, for conversion to an analog signal. The CODEC will then present the
signal to the receive audio pre-amplifier, then to the audio power amplifier, which drives the
speaker.
• For signaling information, the DSP will decode the message and pass it internally to the
microcontrol unit of the dual-core processor.
RF Input
RX Front End
Harmonic
Filter
ADC
LO
CKO
RX_SSI_ DATA
to VOCON Board
XTAL
Filter
ABACUS III - RX Back End
Antenna
Switch
LNA
Tuneable
Preselector
Filter
Tuneable
Preselector
Filter
1st
Mixer
1st LO
3
MAEPF-27278-A