Samsung SCH-1900, Service Manual, Page: 13 / 112

Circuit Description
Samsung Electronics 4-3
4-1-4 Audio Section
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(U102). This signal is then applied to the
MSM(U101)'s internal vocoder.
RX AUDIO PATH
The PCM data from the MSM are converted to
audio signal by DAC of CODEC(U102),is then
amplified by the speaker amplifer(U105) to be sent
to the speaker unit.
VOLUME ADJUST
Volume can be adjusted up to 8 steps for the user
to obtain a proper loudness of received signal.
4-1-5 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.
4-1-6 Key Tone Generator
Ring signal (pin49) from MSM(U101) is passed
through LPF consisting of R180, C119, R124, and
C120, amplified at the speaker amp(U105) and
come out to speaker.
Figure 4-1 Baseband Block Diagram