3. TECHNICAL BRIEF
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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 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-ohm interface.
The QTR8200/8600 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 QTR8200/8600 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 QTR8200/8600 IC design achieves this
without allowing FVCO to equal FRF. The QTR8200/8600 IC is able to support UMTS 2100/1900/1800/1700 and
850 mode transmitting. This design guideline shows only UMTS 1900 applications.
[Figure 3.3.2] QTR8200/8600 IC transmitters Block Diagram