Transmitter Section - Samsung SCH-470 Service Manual

Circuit Description

5-3 Transmitter Section

BBA (U401)
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 throuth 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 each filter and the up-converters.
POWER AMP MODULE (U467)
Power Amp module (U467) amplifies signal (24dB
Gain) to be sent out to the base station through the
antenna.
UP CONVERTER (MIXER, U460)
The up-converter (U460) receives the first local
signal to generate 836 °æ12.5 MHz from the BBA.
836 °æ12.5 MHz signal comes out of the mixer
output by subtracting 130 MHz IF signal from 966
°æ12.5 MHz first local signal.
RF AUTOMATIC GAIN CONTROLLER AMP
(U461, U464)
The signal out to the base station should be a
constant level. The TX RF AGC amp controls
power to keep the signal at a constant level.
5-6
RF BAND PASS FILTER (BPF, F451)
The RF BPF ( F451) accepts only a specific
frequency (836 °æ12.5MHz) to send it out to the
base station. The band width is 25 MHz.
POWER SUPPLY SWITCHING (U484)
Power supply switching (Q484) turns on
TX_POWER when the phone is in traffic mode and
supplies power to the circuits.
POWER SUPPLY REGULATOR (U482, U483)
The power supply regulators (U482,U483) supply
a regulated power to each part of transmitter.
U482 supplies 3.6V to TX AGC amp (U461) and
up-converter (U460). U483 supplies 3.0V to power
amp module control circuit (U487).
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