LG L240 Service Manual page 14

3.2.1.1 Front End Part
The RF front end consists of Antenna Switch, quad saw filters and LNAs integrated in transceiver .
Antenna switch is integrated in MMM6027 (Raptor) and quad saw filters are integrated in saw filter
bank. The Received RF signals (GSM850,900, PCS, DCS) are fed into the antenna and Mobile
switch. An antenna matching circuit is between the antenna and the mobile switch. The Antenna
Switch in Raptor is used to control the Rx and Tx paths. And, the input signals TX_ANT_SW_EN,
LB_HB and US_EURO of Raptor are connected to transceiver controller to switch either Tx or Rx
path on. Antenna Switch supports for quad band.
The FEM control logics given below Table 1
Switch Mode
GSM850 Rx
EGSM Rx
DCS Rx
PCS Rx
GSM850 Tx
EGSM Tx
DCS Tx
PCS Tx
The receiver part uses a very low-IF (VLIF) conversion architecture that allows for the on-chip
integration of the DC offset compensation system, eliminating DC offset from the demodulated signal.
The MMM6000 integrates quad differential input LNAs that are matched to the 200 ohm with
balanced-output SAW filter bank through LC matching networks in SAW filter bank.
3.2.1.2 Demodulator and base-band processing
The RX architecture is digital VLIF/DCR. There are four separate LNAs providing functionality for
GSM850, EGSM900, DCS1800 and PCS1900 frequency bands. The LNAs are differential and
provide 30 dB of dynamic range as digital steps, eliminating the need for RX AGC gain. The
quadrature down mixer converts the RF signal to base band. Passive differential and common mode
filtering at the mixer output limits out of band signals in the active stages of the base band section
and results in an IP2 of 55 dBm (including processor gain). The I and Q analog base band signals are
passed through low pass anti-aliasing filters and dc offset correction circuits before being processed
by the analog-to-digital converters.
TX_ANT_SW_EN
Low
Low
Low
Low
High
High
High
High
<Table 1> Control Logics
- 15 -
3. Circuit Description
LB_HB US_EURO
Low
Low
High
High
Low
Low
High
High
Low
High
High
Low
Low
High
High
Low