Samsung SCH-2000, Service Manual, Page: 15 / 97

Samsung Electronics 4-5
Circuit Description
4-3 Transmitter Section
POWER AMP MODULE
Power Amp Module (U407) amplifies signal to be
sent out to the base station through the antenna.
DRIVER AMP
The driver amp (Q413) allows the signal input to
the Power Amp Module (U407) to be within a
specified level.
UP CONVERTER (MIXER)
The up-converter (U405) receives the first local
signal to generate 1880
°æ
30MHz from the signal
controlled by TX AGC amp (U404). 1880
°æ
30MHz
signal comes out from the mixer output by adding
130MHz IF signal to 1750
°æ
30MHz first local
signal. The driver amp's reference number is Q413
and up converter's reference number is U405.
IF AUTOMATIC GAIN CONTROLLER AMP
The signal out to BBA (Base Band Asic) should be
a constant level. The TX IF AGC amp (U404)
controls power to keep the signal at a constant
level. Dynamic range is 85 dB, up gain +40dB, and
down gain -45dB.
ANTENNA
ANT1 allows signals to send to receive from the
base station.
RF BAND PASS FILTER (BPF)
The RF BPF (F402) accept only a specific frequency
(1880
°æ
30MHz) to send it out to power amp
MMIC. The band width is 60MHz.
POWER SUPPLY SWITCHING
Power supply switching (Q412) turns on TX
POWER when the phone is in traffic mode and
supplies power to the circuits.
ISOLATOR
Isolator (I401) is used to reduce a reflected signal
to protect the power amp MMIC from being
damaged.
POWER SUPPLY REGULATOR
The power supply regulator (U413,U414) supply a
regulated power to each part of transmitter.
U413 supplies 3.6V to Tx driver (Q413) and Power
Amp Module (U407). U414 supplies 3.3V to the
others.