LG KU950 Service Manual page 26

3. TECHNICAL BRIEF
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 at the output of the charge pump. This error signal is filtered by the
loop filter and applied to the VCO, tuning the output frequency such that the error is decreased.
Ultimately the loop forces the error to approach zero and the PLL is phase and frequency locked.
Many key PLL performance characteristics are largely determined by the loop filter design - stability,
transitory response, settling time, and phase noise.
3.4.2 Transceiver PLL (PLL1)
All LO functional blocks for the other handset modes(UMTS Tx, EGSM Tx/Rx, DCS Tx/Rx, PCS
Tx/Rx) are integrated into the RTR6250 IC except the loop filter components (Figure 3.4.2-1). On-chip
circuits include reference divider, phase detector, charge pump, VCO, feedback divider, and digital
logic status. The functional description given in Section 1.4.1 for the UMTS Rx PLL applies to the
Transceiver PLL as well.
Figure 3.4.2-1 Transceiver PLL functional block diagram
The off-chip loop filter allows optimization of key PLL performance characteristics (stability, transitory
response, settling time, and phase noise) for different applications. Guidelines are provided in the next
subsection for proper implementation of this critical circuit.
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