Umts Mode - LG GT540 Service Manual

3.3 UMTS MODE

3.3.1 UMTS RECEIVER
The UMTS duplexer receiver output is routed to LNA circuits within the RTR6285 device as shown in Figure 1-4. The
UMTS Rx input is provided with an on-chip LNA that amplifies the signal before a second stage filter that provides
differential downconverter as shown in Figure 1-5. This second stage input is configured differentially to optimize
secondorder intermodulation and common mode rejection performance. The gain of the UMTS frontend amplifier
and the UMTS second stage differential amplifier are adjustable, under MSM control, to extend the dynamic range
of the receivers. The second stage UMTS Rx amplifiers drive the RF ports of the quadrature RF-to-baseband
downconverters. The downconverted UMTS Rx baseband outputs are routed to lowpass filters having passband
and stopband characteristics suitable for UMTS Rx processing. These filter circuits allow DC offset corrections, and
their differential outputs are buffered to interface shared with GSM Rx to the MSM IC. The UMTS baseband outputs
are turned off when the RTR6285 is downconverting GSM signals and on when the UMTS is operating.
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[Figure 1-4] UMTS Receiver Inputs Topologies
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3. TECHNICAL BRIEF
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