LG CU500 - Cell Phone, 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 CU500’s receiver functions are split between the three RFICs as follows:
• UMTS-850,1900 operation uses the RFL6202 LNA and RFR6202 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 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 2 -controlled
parameters.
RF Front end consists of antenna, antenna switch module(CXG1198AEQ), and three RX saw
filters(GSM850, GSM900, DCS and PCS). The antenna switch module allows multiple operating
bands and modes to share the same antenna. In CU500, a common antenna connects to one of eight
paths: 1) UMTS-850 Rx/Tx, 2) UMTS-1900 Rx/Tx, 3) GSM-850 Rx, 4) GSM-900 Rx, 5) GSM-850
GSM-900 Tx, (Low 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/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.
IN_A IN_B IN_C
GSM850/GSM900 TX HIGH HIGH LOW
DCS/PCS TX HIGH LOW LOW
GSM 850 RX LOW HIGH LOW
UMTS 850 HIGH LOW HIGH
DCS RX LOW HIGH HIGH
PCS RX LOW LOW HIGH
UMTS 1900 HIGH HIGH HIGH
GSM 900 LOW LOW LOW
Table 3.2.1 Antenna Switch Module Control logic