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LGE Internal Use Only
Copyright © 2009 LG Electronics. Inc. All right reserved.
Only for training and service purposes
3. Technical Brief
GM750
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-
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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.
Содержание Vodafone GM750
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