LG U880, Руководство по обслуживанию, Страница: 26 / 197

3. TECHNICAL BRIEF
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Most UMTS Rx PLL circuits are included within the RTR6250 IC: reference divider, phase detector,
charge pump, feedback divider, and digital logic that generate LOCK status. The buffered 19.2 MHz
TCXO signal provides the synthesizer input (REF), the frequency reference to which the PLL is phase
and frequency locked.
The reference is divided by the R-Counter to create a fixed frequency input to the phase detector, FR.
The other phase detector input (FV) varies as the loop acquires lock, and is generated by dividing the
RX_VCO_IN frequency using the feedback path.s N-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 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 1.4.2-1). 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