LGC-340/345W
20
LGIC
LG Information & Communications, Ltd.
1.2 Description of Receive Part Circuit
1.2.1 Duplexer
The duplexer(DP1) consists of the receive part bandpass filter (BPF) and the transmit part bandpass filter (BPF)
which have the function of separating transmit/receive signals in the full duplex system using the transmit/receive
common antenna. The transmit part BPF is used to suppress noises and spurious waves entering the receive band
among transmit signals in order to prevent the drop in receive sensitivity characteristics. The receive part BPF
blocks the signals sent out from entering the receive end in order to improve sensitivity characteristics.
Insertion loss (IL) in the transmit band is 2.4dB (Max), whereas IL in the receive band is 3.3dB (Max).
The receive band attenuation amount of transmit filter is 58dB (Min) and the transmit band attenuation amount of
receive filter is 43dB or more (Min).
1.2.2 Downconverter
The downconverter is made up largely of low noise amplifiers(U2) and a frequency active gain DOWN
mixer(U14).
RF signals (869.04 ~ 893.97 MHz) received from the Duplexer are amplified after obtaining the gain of 19dB
through the LNA. Then, they are passed through the BPF. At this time, about 3dB IL is generated.
The output signals are fed to the mixer input terminal(U14.4). The mixer synchronizes the RF signals with local
oscillating signal that has been inputted to the local input terminal(U14.3) in order to create the IF (85.38MHz)
signals. At this time, the conversion gain of 10dB is added the signals.
Local oscillating signals through other paths are fed into the mixer of transmit terminal.
The signal suppression rate of RF signal band on local oscillating signals is 40dB on th average whereas the IF
signal band signal suppression rate is 33 dB.
IF signals have two paths after passing the Mixer. One is the digital path (CDMA) while the other is the analog
path (FM).
The paths to be selected are determined by receiving output signals FM/ of MSM3000 through the IF select
terminal. IF signals that have selected the FM path are inputed to FM IF BPF(F8) for FM through the FM path.
IF signals that have selected the CDMA path are passed CDMA IF saw filter(F6) and then, are inputed to
IFR3000.
