Samsung SPH-A900 Service Manual page 11

Circuit Description
Driver Amp
The driver amp(U402 ; included in S1M8690X) allows the signal to be inputted to the power
amp(PAM400) as a specified level.
Up-converter(Mixer)
F * 0.7999
The up-converter(U402 ; also included in S1M8690X) receives the local signal
Tx
and signal controlled by TX AGC amp(in S1M8690X) to generate Tx RF signal 1880±30MHz
F * 0.7999
which signal comes out from the mixer output by adding local signal.
Tx
F
means TX RF signal Frequency.
Tx
Automatic Gain Control Amp
The TX IF AGC amp (in S1M8690X) controls gain of AGC to deliver power level needed at
driver amp. Its control voltage varies from 0.2V to 2.5V.
2-3. CDMA Section
2-3-1. Receiver
Low Noise Amplifier(LNA)
The low noise amplifier(It is included RFL6000 : U300) amplifies a weak signal received from
the base station to obtain the optimum signal level.
RF Band Pass Filter(Rx RF SAW Filter)
The RF BPF in F300 passes only a specific frequency(881.49±12.5 MHz) from the signal
received from the mobile station. The bandwidth is 25 MHz.
Voltage Controlled Oscillator
The VCO(VCO300) generates the signal having 1715 ~ 1788MHz frequency range.
The VCO's output frequency is changed by control voltage. The PLL in S1M8690X generates this control
signal and this signal is changed into DC control voltage by R-C Loop filter.
2-7
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