Samsung SCH-3500 series Service Manual page 22

6-1-4 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 (U902). This
signal is then applied to the MSM (U908)'s internal
vocoder.
RX AUDIO PATH
The PCM data out from the MSM is converted to
audio signal by ADC of CODEC (U902), is then
amplified by CODEC (U902) 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 ±2.9 kHz/dev, attack time is 3 mS,
and release time is 13.5 mS.
Limiter
The limiter performs to cut ±0.53 Vp-p or higher
audio signal level so that the FM frequency
deviation is not over ±12 kHz/dev. The function is
used to avoid confusion over phone line. LPF is
used to reduce a specific high frequency of limited
signal.
SAMSUNG Proprietary-Contents may change without notice
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 ±2.9 kHz/dev, attack time is 3 mS, and
release time is 13.5 mS.
Volume Adjust
Volume can be adjusted up to 6 steps for the user to
obtain a proper loudness of received signal.
6-1-5 TX WBD, ST, And SAT
These signals are generated from MSM. The
modulation level of TX WBD and ST is
±8 kHz/dev, and SAT is ±2 kHz/dev.
6-1-6 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
signal's period generated from the MSM timer.
6-4
Circuit Description