LG U8110 Service Manual page 86

3. TECHNICAL BRIEF
E. RF Mixer and Buffer
The RF mixer converts the signal output from the IF BP filter from an intermediate frequency (IF) to the
final radio frequency (RF). The mixer can be switched between three different gain levels: high gain
(HG), medium gain (MG), and low gain (LG).
The LO buffer provides the buffering for either an internal LO signal generated within the internal
RFPLL, or an external LO signal applied to the RFLO/RFLOBAR pins. External DC blocking is
necessary for the external LO signal.
The RF buffer is used to drive an external PA stage. The buffer is of an open-collector design. The
gain switching together with the VGA amplifier at IF will enable an output power control in 0.25 dB
steps over no less than 80dB.
The programmable bias in the high and mid-gain settings is specified as a reduction of bias current
from the maximum bias condition. It should achieve a reduction of bias current from the nominal value
of 17mA to 3mA (signal ended) in 7 steps.
Figure 3-13. Block Diagram of RF Mixer and Buffer.
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