Only For Training And Service Purposes - LG CT815 Service Manual

3.3.2 UMTS TRANSMITTER
The UMTS TX path begins with differential baseband signals (I and Q) from the MSM device.
These analog input signals are amplified, filtered, and applied to the quadrature upconverter mixers.
The up-converter output is amplified by multiple variable gain stages that provide transmit AGC control.
The AGC output is filtered and applied to the driver amplifier; this output stage includes an integrated
matching inductor that simplifies the external matching network to a single series capacitor to achieve
the desired 50-Ω interface.
The RTR6285 UMTS output is routed to its power amplifier through a bandpass filter, and delivers fairly
high-level signals that are filtered and applied to the PA. Transmit power is delivered from the duplexer
to the antenna through the switch module.
The transceiver LO synthesizer is contained within the RTR6285 IC with the exception of the off-chip
loop filter components and the VC-TCXO. This provides a simplified design for multimode applications.
The PLL circuits include a reference divider, phase detector, charge pump, feedback divider, and digital
logic generator.
UMTS TX. Using only PLL1, the LO generation and distribution circuits create the necessary LO signals
for nine different frequency converters. The UMTS transmitter also employs the ZIF architecture to
translate the signal directly from baseband to RF.
This requires FLO to equal FRF, and the RTR6285 IC design achieves this without allowing FVCO to
equal FRF.
The RTR6285 IC is able to support UMTS 2100/1900/1800/1700 and 850 mode transmitting. This
design guideline shows only UMTS 2100 applications.
Copyright © 2009 LG Electronics. Inc. All right reserved.

Only for training and service purposes

3. TECHNICAL BRIEF
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LGE Internal Use Only