LG B2070, Service Manual

Page: 15 / 139

3. TECHNICAL BRIEF
- 14 -
(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 imagereject filters and the IF SAW
filter required in conventional super-heterodyne architectures.
A. RF front end
RF front end consists of Front End Module(FL500) and Quad band LNAs integrated in
transceiver (U500).
The Received RF signals(GSM 925MHz ~ 960MHz, DCS 1805MHz ~ 1880MHzPCS
1930MHz ~ 1990MHz) are fed into the antenna or Mobile switch. The Front End
Module(FL500) is used to control the Rx and Tx paths. And, the input signals VC1, VC2,
VC3 of a FL501 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
GSM850 (869-849 MHz) or E-GSM 900 (925-960MHz) bands. The DCS input supports
theDCS 1800 (1805-1880 MHz) band. The PCS input supports the PCS 1900 (1930-
1990MHz) band.
The LNA inputs are matched to the 150Ω 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 VC2 VC3
DCS, PCS Tx
GSM / DCS Rx
PCS / DCS Rx
GSM Tx
0 V
0 V
0 V
2.5 ~ 3.0 V
0 V
0 V
0 V
2.5 ~ 3.0 V
0 V
0 V
0 V
2.5 ~ 3.0 V