LG CU920 Manual page 24

3. TECHNICAL BRIEF
3.3.2 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 up-converter 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 RTR6275 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 RTR6275 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 RTR6275 IC design achieves this without allowing FVCO to equal FRF.
The RTR6275 IC is able to support UMTS 2100/1900 and UMTS 850 mode transmitting. This design
guideline shows only UMTS 1900 and UMTS 850 applications.
LGE Internal Use Only Copyright © 2008 LG Electronics. Inc. All right reserved.
- 26 -
Only for training and service purposes