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6-7
Circuit Description
6-3 CDMA Section
6-3-1 Receiver
LOW NOISE AMPLIFIER & DOWN
CONVERTER (U300)
U300 includes LNA and Down Converter and
supports Tri_mode CDMA & AMPS LNA/DOWN
Converter.
The low noise amplifier featuring 1.4dB Noise Figure
and 15.7dB gain amplifies a weak signal received
from the base station to obtain the optimum signal
level.
First local signal is applied to this down converter.
The down converter transfers the signal amplified at
the LNA into 183.6 MHz IF signal. 183.6MHz IF
signal is made by subtracting 881.5±12.5MHz RF
signal from 1065.1±12.5MHz first local signal.
IF AUTOMATIC GAIN CONTROLLER(AGC)
AMP
183.6MHz IF signal is applied to IF AGC amplifier(in
IFR3000), AGC output level is applied to next stage in
IFR3000.. The AGC amp keeps the signal at a constant
level by controlling the gain. Dynamic range is 90 dB,
and its control voltage varies from 0.2V to 2.5V.
RF BAND PASS FILTER (F300)
The RF BPF passes only a specific frequency
(881.49±12.5 MHz) from the mobile station. The width
is 25 MHz.
IF SAW BAND PASS FILTER (F304)
If SAW BPF is used for CDMA system having
1.23MHz wide band. The filter also climinates the
image product generated at the mixer.
VOLTAGE CONTROLED OSCILATOR(U382)
A dual-band VCO generates 1391.82MHz LO and PLL
circuit whose other narrowband tunning range
supports both PCS and Cellialr operation.
PHASE LOCKED LOOP(PLL) (U340)
Input reference frequency is generated at VCTCXO
(U380) and the divided signal is generated at VCO.
The PLL compares the two signals and generates the
desired signal with a pre-programmed counter which
controls voltage.
VOLTAGE CONTROLLED TEMPERATURE
COMPENSATED CRYSTAL OSCILLATOR
(U390)
It provides 19.68Hz reference frequency to PLL (U340),
RFT3100(U400), and IFR3300(U300).
A correct frequency tuning is made by the voltage
control.
6-3-2 Transmitter
RFT3100 (U400)
The RFT3100 contains Up converter, Automatic gain
control amplifier(AGC),and Driver Amplifier.
RFT3100 accepts analog data signal, so there is no
need for additional Modulation Circuit.
Up Converter and Driver Amplifier's gain are
controlled through the Serial Bus Interface(SBI).
RF BANDPASS FILTER(F300)
The Bandpass Filter(BPF) accepts only a specific
frequency(836±12.5MHz) to send it to next RF stage.
The band width is 25MHz.
POWER AMP MODULE (U444)
Power amp module amplifies RF signal and send it to
base station through the antenna.
