Only For Training And Service Purposes - LG KS10 Service Manual

The RFR6250 IC accommodates single-ended or differential LO inputs; if single-ended, either pin can
be active. AC-couple the inactive pin to ground using an appropriately valued capacitor (12 pF is used
in KS10). The 27 pF capacitor should be used to AC-couple the active pin to the VCO signal. Using
only the selected VCO signal, the RFR6250 IC LO generation and distribution circuits create the
necessary LO signals for the active quadrature downconverter.
A sample of the downconverter LO is buffered and routed from RFR6250 IC pin 19 to RTR6250 IC pin
32 (RX_VCO_IN). This signal requires a terminating resistor near the RTR6250 IC input pin and an AC
coupling capacitor that assures the internal RTR6250 IC biasing is not disrupted in the example. Good
microstrip or stripline controlled-impedance techniques must be used.
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 RCounter 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.
Copyright © 2007 LG Electronics. Inc. All right reserved.

Only for training and service purposes

3. TECHNICAL BRIEF
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