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Copyright © 2008 LG Electronics. Inc. All right reserved.
Only for training and service purposes
LGE Internal Use Only
3. TECHNICAL BRIEF
Figure 3-7-8. Front-End Module
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.
Содержание TU750
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