Samsung SCH-3500 series Service Manual page 23

Circuit Description
6-2 Receiver
(For PCS)
LOW NOISE AMPLIFIER (LNA)
The low noise amplifier featuring 1.6 dB Noise
Figure and 20dB 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 transfers the signal amplified
at the LNA into 210.38 MHz IF signal. 210.38 MHz
IF signal is made by subtracting 1960 ±30 MHz RF
signal from 1750 ± 30 MHz first local signal. The
LAN is Q101 and down converter is U101.
LOCAL BUFFER AMPLIFIER
Buffer (Q203) amplifies signal to be applied to the
local input of the down converter (U101) when a
phase is locked between U201 and U204.
RF BAND PASS FILTER (BPF)
The RF BPF (F104) passes only a specific frequency
(1960±30MHz) from the signal received from the
mobile station. The band width is 60MHz.
IF SAW BAND PASS FILTER
IF SAW BPF (F106) is used for CDMA system
having 1.23MHz wide band and ±630 kHz
bandwidth. The filter also climinates spurious
signals generated at the mixer.
SAMSUNG Proprietary-Contents may change without notice
VOLTAGE CONTROLLED OSCILLATOR
The VCO (U201) generates the signal having
1750 MHz center frequency and ±30 MHz deviation
with voltage control. PLL IC (U204) controls this
signal.
PHASE LOCKED LOOP (PLL)
Input reference frequency is generated at VCTCXO
(U205) and the divider signal is generated at VCO.
PLL 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 PLL
(U204) and IFT (U501), IFR (U103). A correct
frequency tuning is made by the voltage control.
TEMPERATURE TO VOLTAGE CONVERTER
The Temperature to Voltage Converter (U341)
detects temperature. It is used to compensate active
component characteristics due to the temperature
difference.
DUPLEXER
Duplexer (F101) controls to transmit through the
antenna only the signals within acceptable Tx
frequency range (1880 ±30 MHz). It also matches
LNA (U401) input in receiving part and PA out in
transmitter part with the antenna.
6-5