Gsm Mode - LG KU800 Service Manual

3. TECHNICAL BRIEF

3.2 GSM Mode

3.2.1 GSM Receiver
The Dual-mode KU800's receiver functions are split between the three RFICs as follows:
• UMTS-2100 operation uses the RFR6250 Receiver ICs to implement the receive signal path,
accepting an RF input and delivering analog baseband outputs (I and Q).
• EGSM-900, DCS-1800, and PCS-1900 modes both use the RTR6250 IC only. Each mode has
independent front-end circuits and down-converters, but they share common baseband circuits (with
only one mode active at a time). All receiver control functions are beginning with SBI
parameters.
RF Front end consists of antenna, Front End Module(including ASM,three Rx SAW filter;
GSM,DCS,PCS). The antenna switch module allows multiple operating bands and modes to share the
same antenna. In KU800, a common antenna connects to one of four paths : 1) DCS 1800/PCS 1900
RX 2) GSM900 RX 3) GSM 900 TX/ WCDMA 4) DCS 1800 /PCS 1900 TX operation requires
simultaneous reception and transmission, so the UMTS Rx/Tx connection is routed to a duplexer that
separates receive and transmit signals.
GSM900, DCS, and PCS operation is time division duplexed, so only the receiver or transmitter is
active at any time and a frequency duplexer is not required.
ANT_SELO
GSM 1800/GSM 1900 RX
GSM 850/GSM 900 RX
GSM 850/GSM 900 TX/WCDMA
GSM 1800/GSM 1900 TX
The GSM900, DCS, and PCS receiver inputs of RTR6250 are connected directly to the transceiver
front-end circuits (filters and antenna switch module). GSM900, DCS, and PCS receiver inputs are
similar to the RFR6250 UMTS Rx input in that they also use differential configurations to improve
common-mode rejection and second-order non-linearity performance. The balance between the
complementary signals is critical and must be maintained from the RF filter outputs all the way into the
IC pins
2 The RFIC operating modes and circuit parameters are MSM-controlled through the proprietary 3-line Serial Bus Interface (SBI). The Application
Programming Interface (API) is used to implement SBI commands. The API is documented in AMSS Software - please see applicable AMSS
Software documentation for details.
ANT_SEL1
GSM_PA_BAND
LOW LOW
LOW
HIGH LOW
HIGH
LOW HIGH
HIGH HIGH
Table. Antenna Switch Module Control logic
MODE
GSM900
GSM
DCS1800/PCS1900
DCS/PCS
OFF
- 20 -
2 -controlled
TX_VCO_EN_O_N TX_VCO_EN_1_N
HIGH LOW
LOW HIGH
HIGH HIGH