LG C3400 Service Manual page 13

3. TECHNICAL BRIEF
(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 super-heterodyne architectures.
A. RF front end
RF front end consists of Antenna Switch(FL500), two SAW Filters(FL401, FL402) and dual
band LNAs integrated in transceiver (U502).
The Received RF signals(GSM 925MHz ~ 960MHz, DCS 1805MHz ~ 1880MHz) are fed into
the antenna or Mobile switch.
The Antenna Switch(FL500) is used to control the Rx and Tx paths. And, the input signals
VC1 and VC2 of a FL500 are directly connected to baseband controller to switch either Tx or
Rx path on.
The logic and current is given below Table 3-1.
Three differential-input LNAs are integrated in SI4205. The GSM input supports the GSM 850
DCS TX
GSM TX
GSM/DCS RX
(824-849 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 150ߟ 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).
Table 3-1 THE LOGIC AND CURRENT
VC1
0V
2.5 ~ 3.0V
0V
- 12 -
VC2
2.5 ~ 3.0V
0V
0V
Current
10.0 mA max
10.0 mA max
< 0.1 mA