Umts Mode - LG CU920 Manual

3.3 UMTS Mode

3.3.1 Receiver
The UMTS duplexer receiver output is routed to LNA circuits within the RFR6275 device.
UMTS LNA circuits(one for low-band UMTS and one for high-ban UMTS path) separated from all other
receive functions contained within the RFR6275 receiver IC to improve mixer LO to RF isolation a
critical parameter in the ZIF architecture. Isolation is further improved using high-reverse isolation
circuits into the LNA designes.
The LNA gains are stepped via API control. The IC operating mode and LNA bias currents
reautomatically adjusted via software to minimize DC power consumption.
The UMTS Rx input is provided with an on-chip LNA that amplifies the signal before a second stage
filter that provides differential downconverter. This second stage input is configured differentially to
optimize second-order 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 RTR6275 is downconverting GSM signals and on when the UMTS is operating.
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Fig. 3.2.2 GSM Transmitter matching
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3. TECHNICAL BRIEF
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