Only For Training And Service Purposes - LG L704I Service Manual

3. TECHNICAL BRIEF
The GSM900, DCS, and PCS receiver inputs of RTR6275 are connected directly to the transceiver
front-end circuits(filters and front end module). GSM900, DCS, and PCS receiver inputs are similar to
the RFR6275 UMTS Rx input in that they also use differential configurations to improve common-mode
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 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 front end module.
The GSM900, DCS, and PCS receive signals are routed to the RTR6275 through band selection filters
and matching networks that transform single-ended 50Ωsources 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 RTR6275 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 (an interface shared with the RFR6275 UMTS receiver outputs
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Only for training and service purposes