LG F1200 Service Manual page 14

(1) RF Front End
RF front end consists of Antenna Switch Module with SAW filter for triple band (FL100), triple
band LNAs integrated in transceiver (U102).
The Received RF signals (EGSM 925MHz ~ 960MHz, DCS 1805MHz ~ 1880MHz, PCS 1850 ~
1990MHz) are fed into the antenna or mobile switch. An antenna matching circuit is between the
antenna and the mobile switch. The Antenna Switch (in FL100) is used for control the Rx and
TX paths. And, the input signals ANT1, ANT2 and ANT3 of a FL100 are directly connected to
baseband controller to switch either TX or RX path on and select bands. Ant S/W module
(FL100) is an antenna switch module for dual band phone. The logic and current is given below.
Mode
EGSM TX
DCS/PCS TX
EGSM RX
DCX RX
PCS RX
The receiver part uses a low-IF receiver architecture that allows for the on-chip integration of the
channel selection filters, eliminating the external RF image reject filters and the IF SAW filter
required in conventional super-heterodyne architecture. The Si4206[U102] integrates three
differential input LNAs that are matched to the 200 ohm balanced-output SAW filters through
external LC matching networks.
Figure 1. RECEIVER PART Block Diagram
ANT1
H
L
L
L
L
Table 2. BAND/RTX SELECTION
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3. TECHNICAL BRIEF
ANT2
L
H
L
L
L
ANT3
L
H
L
L
H