LG U970, Service Manual

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The GSM900, DCS, and PCS receiver inputs of RTR6275 are connected directly to the transceiver
front-end circuits(filters and antenna switch module). GSM900, DCS, and PCS receiver inputs 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 switch module.
The GSM900, DCS, and PCS receive signals are routed to the RTR6275 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 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
3. TECHNICAL BRIEF
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