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Copyright © 2008 LG Electronics. Inc. All right reserved.
Only for training and service purposes
3. TECHNICAL BRIEF
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3.2 GSM Mode
3.2.1 GSM Receiver
The Dual-mode CU920/CU915’s receiver functions are split between the three RFICs as follows:
■ UMTS-850, UMTS-1900 operation uses the RFR6275 receiver ICs to implement the receive signal
path, accepting an RF input and delivering analog baseband outputs (I and Q).
■ GSM-850, GSM-900, DCS-1800, and PCS-1900 modes 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 CU920/CU915, a common
antenna connects to one of six paths: 1) UMTS-850 Rx/Tx, 2) UMTS-1900 Rx/Tx, 3) GSM-850 Rx, 4)
GSM-900 Rx, 5) GSM- 850/900 Tx(lo band Tx’s share the same path), 6) DCS-1800 Rx, and 7) DCS-
1800, PCS-1900 Tx(High Band Tx’s share the same path), 8) 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. GSM850/900, 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_SEL0 ANT_SEL1 ANT_SEL2 ANT_SEL3
GSM900/GSM850 TX HIGH HIGH LOW LOW
DCS/PCS TX HIGH LOW LOW LOW
GSM 850 RX LOW LOW LOW LOW
GSM 900 RX LOW LOW HIGH LOW
DCS RX LOW HIGH HIGH LOW
PCS RX LOW HIGH LOW LOW
UMTS 850 HIGH LOW HIGH LOW
UMTS 1900 HIGH HIGH HIGH HIGH
ANENNA SWITCH MODULE LOGIC
Table. 3.2.1 Antenna Switch Module Control logic
[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.
LMSP4LMA_573TEMP_Rew B Later
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