Samsung SCH-A302 Service Manual page 48

SCH-A302
Circuit description & Circuit Diagrams
2. CDMA
(1) Receiver
Low Noise Amplifier(LNA)
The low noise amplifier featuring 1.8 dB Noise Figure and 14.5 dB gain amplifier a weak signal receiver
from the base station to obtain the optimum signal level.
Down Converter(MIXER)
First local signal is applied to this down converter. The down converter tranfers the signal amplified at
the LNA into 85.38 MHz IF signal. 85.38 MHz IF signal is made by subtracting 881 ± 12.5 MHz RF
signal 966 ± 12.5 MHz first local signal.
The LNA and down converter is U361.
RF Band Pass Filter(BPF)
The RF BPF(F303) passes only a specific frequency(881.49 ± 12.5 MHz) from the signal received from the
mobile station. The width is 25 MHz.
IF SAW Band Pass Filter(CDMA)
If SAW BPF(F200) is used for CDMA system having 1.23 MHz wide band and ± 630 kHz bandwidth.
The filter also eliminates the image product generated by the mixer.
Voltage Controlled Oscillator, Phase Locked Loop(PLL)
The VCO+PLL (OSC402 , U402) generates the signal having 966 MHz center frequency
and ± 12.5 MHz deviation with voltage control. The VCO , PLL Module(OSC402, U402) controls this
signal.
Input reference frequency is generated at VC-TCXO(OSC402, U402) and RF local signal is generated at
VCO , PLL (OSC402, U402). The VCO , PLL (OSC402, U402) compares the two signals and generates the
desired signal with a preprogrammed counter which controls voltage.
Voltage Controlled Temperature Compensated Crystal Oscillator
It provides 19.68 MHz reference frequency to VCO , PLL (OSC402, U402) and RFT3100(U204),
IFR(U302). A correct frequency tunning is made by the voltage control.
Duplexer
Duplexer(F302) controls to transmit through the antenna only signals within acceptable TX frequency
range(836.03 ± 12.5 MHz). It also matches LNA(U360) input in receiving part and PA output in
transmitter part with the antenna.
(2) Transmitter
Power Amp
Power amp module(U201) amplifiers the signal to be sent out to the base station through the antenna.
RFT3100
The RFT3100(U204) receives the first local signal to generate 836.03 ± 12.5 MHz.
836.03 ± 12.5 MHz signal comes out from the mixer output by substracting 130.38 MHz IF signal to
967.41 ± 12.5 MHz first local signal.
Antenna
Antenna allows signal to send to receive from the base station.
SAMSUNG Proprietary-Contents may change without notice
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