Only For Training And Service Purposes - LG GT500 Service Manual

3. TECHNICAL DESCRIPTION
3.7.4. Front-End Module (FEM)
A single antenna is used for all bands. The single antenna is used for all transmission and reception.
The Front End block connects the proper block in the radio system to the antenna. The Front End has two
inputs for EDGE/GSM/GPRS, one for low band (850/900 MHz) and one for high band (1800/1900 MHz). The
EDGE/GSM/GPRS power amplifier output is filtered by the low pass filter in the Front End and then
connected to the antenna through a switch. In receive mode, the EDGE/GSM/GPRS signal from the antenna
passes through the switch to one of the four receive SAW filters. The SAW filter provides receive
band selectivity.
In GSM/GRPS/EDGE systems, transmit and receive operations are divided in time and the switch connects
the proper block in accordance with the mode of operation (that is, transmit or receive; one at a time).
In WCDMA the transmit outputs from the WCDMA transceiver are filtered by an external SAW filter that
cleans up the spectrum. The SAW filter output is connected to the power amplifier, one for each band. For
power control, a sample of the transmit output is taken by a directional coupler and converted to a DC level
by the power detection circuit. This signal is used to control the transmitter output power. The transmit
signal passes through an isolator and then a duplexer. The duplexer output is selected by the switch in the
Front End for connection to the antenna. In WCDMA receive mode the signal from the antenna is switched
by the Front End to the correct duplexer. The output from the duplexer is connected to the LNA input in the
WCDMA receiver.
LGE Internal Use Only
Figure 3-7-10. Front-End Module
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Only for training and service purposes