Motorola IMPRES Tetra MTP700, Detailed Service Manual

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TRANSCEIVER 800 MHz MTP700 Portable Radio / Detailed Service Manual 4.2 - 25
Radio Audio System
See Figure 4.2-12
The audio system consists of the GCAP3 IC (U200) and the DSP (U301), both are
located on the main board.
The GCAP3 perform the analog task and part of the digital task of the audio system.
Tx Path
Audio speech is fed either to the internal microphone or the external microphone. The
signals reach the GCAP3 IC. In the GCAP3 IC, a fix gain amplifier (A3 or A5) provides the
signal amplification, the multiplexer (MUX) selects the active input and the Programmable
Gain Amplifier (TxPGA) adjust the path gain according to the radio mode of operation.
Finally, the A/D converts the analog signal into digital format and transfers it to the DSP.
The DSP performs the functions of audio filtering, ACELP speech compression, forward
error correction (FEC), digital modulation, and transfers the data to the RF section. When
the radio is operating in the telephone interconnect mode, the DSP performs the required
tasks such as echo and noise reduction.
Rx Path
The digital output signal from the receiver is fed to the DSP which performs the functions
of digital de-modulation, FEC, ACELP speech de-compression, and audio filtering. It
transfers the data to the GCAP3 IC. In this IC, the D/A converts the digital audio format to
an analog signal, the Programmable Gain Amplifier (RxPGA) adjusts the path gain
according to the setting of the volume control, and the multiplexer routes the audio to the
active receive path. The audio is fed to A4, single-ended audio power amplifier. It is then
fed to the Audio PA, where most of the amplification is performed and can be selected
either to go through the internal speaker or external speaker. Altenatively, the audio from
GCAP3 can also be sent through A1 to the internal Earpiece.
Figure 4.2-12 Audio Path - Block Diagram
SERIAL
INTER-
FACE
EA
AUDIO_OUT
PGA
A/D
A5
+
-
A3
-
+
A
AUX_MIC -
MI CIN -
VAG
MI C +
MI C -
MI C
PGA
D/A
SPKROUT 1
SPKROUT 2
EXTOUT
A4
-
+
A2
AL RTOUT -
AL RTOUT +
A1
+
-
-1
SPKR+
SPKR-
VAG
VAG
RC
FILTER
RC
FILTER
AL RTIN
(A2 INPUT)
AL RTIN
SPKRIN
SPKRIN
(A1 INPUT)
GCAP 3
MUXIN
CODEC
Vcc
OUT1-
OUT1+
OUT2-
OUT2+
IN1-
IN1+
IN2-
IN2+
SVR
MODE
SEL
Stby/
Mute
NC GND2 GND1
VCC1 VCC2
TDA8547 or
ADI part
INT MIC
EXT MIC
INT SPKR
EXT SPKR
EAR-PIECE