LG MG810c, Service Manual

Page: 15 / 134

3.2.1. RF Front End
RF front end consists of Antenna Switch Module with SAW filter for triple band(FL400), triple band
LNAs integrated in transceiver(U401).
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 FL400) is used for control the Rx and TX paths.
And, the input signals ANT1,ANT2 of a FL400 are directly connected to baseband controller to switch
either TX or RX path on and select bands. Ant S/W module(FL400) is an antenna switch module for
dual band phone. The logic and current is given below.
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 SI4210[U401] integrates three differential input
LNAs that are matched to the 200 ohm balanced-output SAW filters through external LC matching
networks.
3. H/W Circuit Description
- 14 -
Figure 1. RECEIVER PART Block Diagram
Table 3-2. BAND/RTX SELECTION
ANT_SW1 ANT_SW2
GSM 850_EGSM RX L L
GSM-850_EGSM TX L H
DCS/PCS RX H L
DCS/PCS TX H H