LG lg530g Service Manual page 29

3. TECHNICAL BRIEF
LG530G
3.3.3 Rx LO circuits
3.3.3 Rx LO circuits
The QSC62x0 device integrates all of the frequency synthesizer functions that generate the UMTS and GSM
receive LO signals (UHF local oscillator, PLL circuits, and loop filter), plus the distribution circuits that deliver the
quadrature LO signals to the two downconverters.
The buffered 19.2 MHz TCXO or XO signal provides the synthesizer input (REF), the frequency reference to
which the PLL is phase and frequency locked. The reference is divided to create a fixed frequency input to the
phase detector, FR.
The other phase detector input (FV) varies as the loop acquires a lock and is generated by dividing the local
oscillator output frequency using the feedback path's counter. The closed-loop will force FV to equal FR when
locked.
If the loop is not locked, the error between FV and FR will create an error signal. This error signal is filtered by
the loop filter and applied to the local oscillator, tuning the output frequency so that the error is decreased.
Ultimately the loop forces the error to approach zero and the PLL is phase and frequency locked.
13/87
LGE Internal Use Only - 29 - Copyright © 2012 LG Electronics. Inc. All right reserved.
Only for training and service purposes