LG KG240, Service Manual

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3. TECHNICAL BRIEF
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(1) Receiver Part
The Aero 2 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 Front End Module(FL400) and dual band LNAs integrated in transceiver (U401).
The Received RF signals(GSM 925MHz ~ 960MHz, DCS 1805MHz ~ 1880MHz PCS 1905MHz ~
1980MHz) 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 ANT_SW1,
ANT_SW2 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
Three differential-input LNAs are integrated in SI4205. The GSM input supports the GSM 850 (864-
894MHz) 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 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).
ANT_SW1 ANT_SW2
GSM Tx 2.5 ~ 3.0 0 V 0V
DCS, PCS Tx 0V 2.5 ~ 3.0 V
GSM Rx 0V 0 V
DCS, PCS Rx 0V 0 V
Table 3-1 THE LOGIC AND CURRENT