Only For Training And Service Purposes - LG TU550 Service Manual

3. TECHNICAL BRIEF
The GSM850, GSM900, DCS, and PCS receiver inputs of RTR6250 are connected directly to the transceiver
front-end circuits(filters and antenna switch module). GSM850, GSM900, DCS, and PCS receiver inputs are
similar to the RFR6202 UMTS Rx input in that they also use differential configurations to improve commonmode
rejection and second-order non-linearity 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 GSM850, GSM900, 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 GSM850, GSM900, 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 impedances optimized for gain
and noise figure. Similar to the RFR, the RTR input uses a differential configuration to improve second-order inter-
modulation 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 or 8-PSK processing. These filter circuits include DC offset corrections. The
filter outputs are buffered and passed on to the MSM6275 IC for further processing (an interface shared with the
RFR6202 UMTS receiver outputs).
LGE Internal Use Only
Figure 3.2.1 RTR6250 RX feature
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Only for training and service purposes