LG U8120, Руководство по обслуживанию

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3. TECHNICAL BRIEF
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3.8 WCDMA Mode
3.8.1 Receiver
The received RF signal on the antenna connector arrives via the antenna switch to the duplexer. The
duplexer directs the signal to the LNA, which resides in Wopy (W-CDMA Receive ASIC) as every other
active part of the radio receiver. The LNA has two different gain settings. From the output of the LNA,
the signal is fed to the input of a RF SAW filter, and then appears at the differential output of the filter.
The differential output of the RF SAW filter is connected to the differential mixer input, and the
received signal is down-converted to a 190MHz IF frequency (with the RFLO signal) by the mixer.
At 190MHz, the signal is filtered in a differential (input and output) IF SAW filter, with the approximate
bandwidth of 4MHz, and then again the signal is fed to Wopy (W-CDMA Receive ASIC), this time to
the differential IF input, which also has a LNA.
From the 190MHz, the signal is mixed down to base-band I and Q which represented signals (using
the IFLO signal). Finally the signals are filtered in low pass filters and amplified in base-band VGAs.
The I and Q represented signals appear at the output of Wopy (W-CDMA Receive ASIC) as differential
voltages.
The large signal gain provided by the processing steps from the antenna down to base-band gives a
DC offset at the outputs of Wopy (W-CDMA Receive ASIC). To eliminate this, there are DC-offset
compensation loops included, one in the VGA of each of the I and the Q signals.
A. IFLO Section
The balanced IFLO signal from an external IFVCO drives the divider to provide qaudrature LO signals
to the RxIF mixers. The LO buffers amplifies the signal to a suitable amplitude and DC level to drive
the RxIF mixers.
Figure 3-9. Block diagram of the IFLO section.