Samsung SCH-211 Service Manual page 25

Circuit Description
5-1-4 Audio Part
TX AUDIO PATH
The voice signal output from microphone is
filtered and amplified by the internal OP-AMP
and is converted to PCM data by the CODEC
(U117). This signal is then applied to the MSM
(U101)Õs internal vocoder.
RX AUDIO PATH
The PCM data out from the MSM is converted to
audio signal by ADC of CODEC (U117), is then
amplified by the speaker amplifier (U111) to be
sent to the speaker unit.
FM TX PATH
Pre-Emphasis Circuit
The circuit features +6dB/oct to reduce signal loss
and noise in Tx path.
Compressor
The compressor features 2:1 level to reduce signal
loss and noise in Tx path. The zero crossing level
of the compressor is ¡¾2.9 kHz/dev, attack time is
3 mS, and release time is 13.5 mS.
Limiter
The limiter performs to cut ¡¾0.53 Vp-p or higher
audio signal level so that the FM frequency
deviation is not over ¡¾12kHz/dev. The function
is used to avoid confusion over phone line. LPF is
used to reduce a specific high frequency of limited
signal.
5-4
RX AUDIO PATH
De-Emphasis Circuit
This circuit is 1st LPF featuring -6dB/oct to reduce
signal loss and noise in Rx path.
Expander
The expander features 1:2 level to reduce signal
loss and noise in Rx path. The zero crossing level
of the expander is ¡¾2.9 kHz/dev, attack time is 3
mS, and release time is 13.5 mS.
Volume Adjust
Volume can be adjusted up to 4 steps for the user
to obtain a proper loudness of received signal.
5-1-5 TX WBD, ST, And SAT
These signals are generated from MSM. The
modulation level of TX WBD and ST is
¡¾8kHz/dev, and SAT is ¡¾2kHz/dev.
5-1-6 Buzzer Driving Circuitry
Buzzer generates alert tone. When the buzzer
receives the timer signal from the MSM, it
generates alert tone. The buzzer level is adjusted
by the alert signalÕs period generated from the
MSM timer.
5-1-7 Key Tone Generator
Ringer signal (pin 49) out from MSM (U101) is
passed through 2 serial LPF consisting of R141,
C145, R145, and C142, amplified at the speaker
amp (U111), and comes out to speaker. In hands-
free mode, the key tone is applied to RX audio
line through the LPF and C153, R142.
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