Only For Training And Service Purposes - LG GU280 Service Manual

3. Technical Brief
3.2.2. Receiver Part
WCDMA Receiver
The antenna collects the base station forward-link signal and radiates the phone's reverse-link signal. In the example of
a multiband, multimode phone (Figure 1.2.2.1), a switch routes the antenna signals to one of the three UMTS Rx/Tx paths,
each beginning with its own band-specific duplexer that separates that band's receive and transmit paths
Each UMTS duplexer provides a differential output signal that is compatible with its QSC LNA input.
The duplexer-to-LNA interface requires a differential matching network (MN) that optimizes the power transfer into
the LNA.
Although there are three UMTS LNAs, only one is active at a time. The active gain-stepped LNA output drives a
shared quadrature downconverter directly — an off-chip inter-stage filter is not required. The elimination of this
filter is achieved by a combination of factors:
- New on-chip QSC processing
- Higher performance achieved by the differential duplexer-to-LNA interface
-Greater duplexer suppression of Tx leakage
The downconverter's RF circuitry includes another gain-stepped amplifier that supplements the LNA gain steps to
further extend the receiver dynamic range. The downconverter translates the active LNA's RF signal directly to
baseband, producing two analog outputs: in-phase (I) and quadrature (Q). The UMTS baseband signals are routed
to lowpass filters whose passband and stopband characteristics are optimized for the active WCDMA waveform.
Both filter outputs are buffered to drive their analog-to-digital converters for digitization. The digital baseband
outputs are routed to QSC baseband circuits for further processing.
LGE Internal Use Only
Figure 1.2.2.1 WCDMA Receiver schematic
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Only for training and service purposes