Circuit Description & Circuit Diagrams - Samsung SCH-A302 Service Manual

Power Consumption Control
When the phone is the sleep mode, it is disabled all the pins except for the basic operation of the MSM.
(4) Audio Part
TX AUDIO PATH
The voice signal from the microphone is filtered and amplified by the internal OP-AMP1 and the
external OP-AMP2, is converted to PCM data by the MSM(U609)'s internal CODEC.
This signal then applied to the MSM's internal vocoder.
RX AUDIO PATH
The PCM data from the MSM is converted to audio signal by ADC of MSM CODEC, is then amplified
by MSM's internal CODEC to be sent to the speaker unit.
FM TX PATH
Pre-Emphasis Circuit
The circuit features +6 dB/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 sued confusion over phone line. LPF is used to reduce a
specific high frequency of limited signal.
RX AUDIO PATH
De-Emphasis Circuit
This circuit is lst LPE featuring -6 dB/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.
Vloume Adjust
Volume can be adjusted up to 3 steps for the user to obtain a proper loudness of received signal.
(5) TX WBD, ST, and SAT
Thess signals are generated from MSM. The modulation level of TX WBD and ST is ± 8 kHz/dev, and
SAT is ± 2 kHz/dev.
(6) Buzzer Driving Circuitry
Buzzer generate 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.
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SCH-A302
Circuit description & Circuit Diagrams
10-3