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Copyright © 2009 LG Electronics. Inc. All right reserved.
Only for training and service purposes
LGE Internal Use Only
3. Technical Brief
Since GSM-850, GSM-900, GSM-1800, and GSM-1900 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 GSM-850, GSM-900, GSM-1800, and GSM-1900
receive signals are routed to the RTR6285 through saw filters and matching networks that transform single-
ended 50-Ω sources to differential impedances optimized for gain and noise figure. The RTR input uses a
differential configuration to improve second-order inter-modulation and common mode rejection
performance. The RTR6285 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 or 8-PSK processing. These filter circuits include DC
offset corrections. The filter outputs are buffered and passed on to the MSM7200A IC for further processing as
shown in Figure 1-3.
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