Gsm Mode - LG L602i Service Manual

3.2 GSM Mode

3.2.1 GSM Receiver
The multi-mode L602i's receiver functions are split between the four RFICs as follows:
• UMTS-800 and UMTS-2100 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).
• 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.
The EGSM, DCS, and PCS receiver inputs of RTR6250 are connected directly to the transceiver front-
end circuits(filters and antenna switch module). EGSM, DCS, and PCS receiver inputs are similar to
the RFR6202 IC UMTS and GPS mixer input in that they also use differential configurations to improve
common-mode rejection and second-order nonlinearity 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.
Since EGSM, DCS, and PCS signals are time-division duplex (the handset can only receive or
transmit at one time), switches are used to separate Rx and Tx signals in place of frequency duplexers
- this is accomplished in the switch module.
The EGSM, DCS, and PCS receive signals are routed to the RTR6250 through band selection filters
and matching networks that transform single-ended 50-Ω. sources to differential 100-Ω load
impedances optimized for gain and noise figure. Similar to the RFR, the RTR input uses a differential
configuration to improve second-order intermodulation and common mode rejection performance. The
RTR6250 input stages include MSM-controlled gain adjustments that maximize receiver dynamic
range.
The amplifier outputs drive the RF ports of the quadrature RF-to-baseband downconverters. The
downconverted baseband outputs are multiplexed and routed to lowpass filters (one I and one Q)
having passband and stopband characteristics suitable for GMSK processing.
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.
3. TECHNICAL BRIEF
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