Only For Training And Service Purposes - LG CT815 Service Manual

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 band selection 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 MSM6280 IC
for further processing as shown in Figure 3-4.
LGE Internal Use Only Copyright © 2009 LG Electronics. Inc. All right reserved.
- 18 -

Only for training and service purposes