Transmitter Section - Samsung SCH-211 Service Manual

Circuit Description
DUPLEXER
Duplexer (F301) controls to transmit through the
antenna only the signals within acceptable Tx
frequency range (836 ¡¾12.5 MHz) and to receive
through the antenna only the signals within
acceptable Rx frequency range (881 ¡¾12.5 MHz).
It also matches LNA (U301) input in receiving part
and PA output in transmitter part with the
antenna.

5-3 Transmitter Section

BASEBAND ANALOG ASIC (BBA)
BBA (U401) consists of ADC, DAC, LPF
(FM/CDMA), divider, VCO, logic control circuit,
PLL, and mixer.
BBA performs a specific function between RF part
and logic part, with MSM. The IF signal out from
Rx IF AGC amp is secondly converted through the
down-converter. The signal passes through the
CDMA or FM filter, converts to digital signal
through ADC, then is sent to MSM. The digital
signal out from MSM converts to analog signal
through DAC. The analog signal converts to the IF
signal through each filter and the up-converter.
POWER AMP MODULE
Power Amp module (U467) amplifies signal (28
dB Gain) to be sent out to the base station through
the antenna .
UP CONVERTER (MIXER)
The up-converter (U461) receives the first local
signal to generate 836 ¡¾12.5 MHz from the signal
controlled by TX IF AGC amp (U460). 836 ¡¾12.5
MHz signal comes out from the mixer output by
subtracting 130 MHz IF signal from 966 ¡¾12.5
MHz first local signal. The driver amp and this
up-converter are packaged into one in U461.
5-6
POWER SUPPLY REGULATOR
The power supply regulator (U381, U382)
generates a regulated power (3.6VR).
ANTENNA
Antenna (ANT1) allows signals to send to receive
from the base station.
IF AUTOMATIC GAIN CONTROLLER AMP
The signal out to the base station should be a
constant level. The TX IF AGC amp (U460) con-
trols power to keep the signal at a constant level.
Dynamic range is 85 dB, up gain +40dB, and
down gain -45dB.
RF BAND PASS FILTER (BPF)
The RF BPF (F451) accepts only a specific
frequency (836 ¡¾12.5MHz) to send it out to the
base station. The band width is 25 MHz.
POWER SUPPLY SWITCHING
Power supply switching (Q483) turns on
TX_POWER when the phone is in traffic mode
and supplies power to the circuits.
ISOLATOR
Isolator (U468) is used to reduce a reflected signal
to protect the power amp module from being
damaged.
POWER SUPPLY REGULATOR
The power supply regulator (U482, U483) supply
a regulated power to each part of transmitter.
U483 supplies 4.7V to TX mixer (U461) and OP
amp (U463). U482 supplies 3.6 V to TX IF AGC
amp (U460).
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