LG U970, Service Manual

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3. TECHNICAL BRIEF
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3.2 GSM Mode
3.2.1 GSM Receiver
The Dual-mode U970/KU970’s receiver functions are split between the three RFICs as follows:
• GSM-900, DCS-1800, and PCS-1900 UMTS-2100 modes bot use the RTR6275 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
2
-controlled parameters.
RF Front end consists of antenna, antenna switch module(LMSP4LMA-573TEM) which includes four
RX saw filters(GSM850, GSM900, GSM900, DCS and PCS). The antenna switch module allows
multiple operating bands and modes to share the same antenna. In U970/KU970, a common antenna
connects to one of six paths: 1) UMTS-2100 Rx/Tx, 2) GSM-900 Rx, 3) GSM-900 Tx, 4) DCS-1800
Rx, and 5) DCS-1800, PCS-1900 Tx(High Band Tx’s share the same path), 6) PCS-1900 Rx. UMTS
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.
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.
[Table 1.1] Antenna Switch Module Control logic