LG C1100, Service Manual, Page: 13 / 127

(1) Receiver Part
The Aero I transceiver uses a low-IF receiver architecture which 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 superheterodyne architectures.
A. RF front end
RF front end consists of Antenna Switch(FL400), two SAW Filters(FL401, FL402) and dual
band LNAs integrated in transceiver (U401).
The Received RF signals(GSM 925MHz ~ 960MHz, DCS 1805MHz ~ 1880MHz) are fed into
the antenna or Mobile switch.
The Antenna Switch(FL400) is used to control the Rx and Tx paths. And, the input signals
VC1 and VC2 of a FL400 are directly connected to baseband controller to switch either Tx or
Rx path on.
The logic and current is given below Table 3-1.
Table 3-1. The Logic and current
Three differential-input LNAs are integrated in SI4205. The GSM input supports the GSM 850
(869-849 MHz) or E-GSM 900 (925-960MHz) bands. The DCS input supports the DCS 1800
(1805-1880 MHz) band. The PCS input supports the PCS 1900 (1930-1990 MHz) band.
The LNA inputs are matched to the 150
Ω
balanced output SAW filters through external LC
matching networks. The LNA gain is controlled with the LNAG[1:0] and LNAC[1:0] bits in
register 05h (Figure 3-2).
VC1 VC2 Current
DCS TX 0V 2.5 ~ 3.0V 10.0 mA max
GSM TX 2.5 ~ 3.0V 0V 10.0 mA max
GSM/DCS RX 0V 0V < 0.1 mA
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3. TECHNICAL BRIEF