Service manual

Motorola Confidential Proprietary
General DescriptionService Manual
63
Analog TX Audio Processing
Digital TX Audio Processing
The analog voice signal coming in through
the microphone is taken by the CODEC and
digitized.The samples produced by this step
are then sent to the DSP.The following steps
are realized with software implementation:
• Nominal TX Mic. Audio adjust amplifier
• Compressor -using a variable gain ampli-
fier that controls the stage’s gain by detect-
ing the power at its output and applying the
result to control the gain
• Deviation Limiter – using an amplifier in
conjunction with a 7
th
order odd polynomial
with two output comparators. The polynomial
reduces the amount of spectral splatter while
the comparators switch as the signal reaches
a high or low threshold.
• Audio mute
• Summing of all analog transmit modula-
tion signals (Mic. Audio, Data/ST, DTMF and
SAT)
A post-limiter splatter filter works with an
up-shelf and a down-shelf filter to limit the
maximum deviation of the transmitter.Data/
Signaling Tone is generated as a sinusoidal
signal using a look-up table, which eases the
filtering requirements for this signal because
of the reduced harmonic energy it entails.
DTMF is generated using look-up tables and
SAT processing is also performed in the
Transmit Audio Circuitry.
The D/A converts audio samples to an ana-
log signal. This signal is then filtered and
applied to the Analog Mod. Input of the syn-
thesizer circuit
The analog voice signal coming in through
the microphone is taken by the CODEC and
digitized. The samples are transmitted to the
DSP where microphone compensation and
echo cancellation processes take place. The
DSP uses ACELP to compress the samples
into data bits.These bits are interleaved with
speech data from adjacent speech frames for
error protection. System messages are then
combined with the data bits and sent to the
data converter for modulation. The data con-
verter modulates the data using differential
quadrature phase shift keying (DQPSK). The
bit streams generated from this step are con-
verted to analog signals which are filtered
before being transmitted.
DSP Lucent 1629
Digital Signal Processor, 80 MIPS, 3 volt op-
eration. It has a DPS1600 core with 16k
words of internal dual-port RAM and 48k
words of ROM. It is contained in a 169 ball
µBGA package with the balls on a 13 x 13mm
grid on 0.8mm centers.
DSP Lucent 1629