Lo Generation And Distribution Circuits - LG KF700Q Service Manual

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3.4 LO generation and distribution circuits

The integrated LO generation and distribution circuits are driven by internal VCOs to support various

modes to yield highly flexible quadrature LO outputs that drive all GSM/EDGE and UMTS band

upconverters and downconverters; with the help of these LO generation and distribution circuits, true

zero-IF architecture is employed in all GSM and UMTS band receivers and transmitters to translate the

signal directly from RF to baseband and from baseband to RF.

Two fully functional fractional-N synthesizers, including VCOs and loop filters, are integrated within the

RTR6280 IC. The first synthesizer (PLL1) creates the transceiver LOs that support the UMTS 2100

transmitter, and all four GSM band receivers and transmitters including: GSM900, DCS1800, and

PCS1900. The second synthesizer (PLL2) provides the LO for the UMTS 2100 receiver. An external

TCXO input signal is required to provide the synthesizer frequency reference to which the PLL is

phase and frequency locked. The RTR6280 IC integrates most of PLL loop filter components on-chip

except two off-chip loop filter series capacitors, and significantly reduces off-chip component

requirement. With the integrated fractional-N PLL synthesizers, the RTR6280 has the advantages of

more flexible loop bandwidth control, fast lock time, and low-integrated phase error

Only for training and service purposes

3. TECHNICAL BRIEF

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LGE Internal Use Only

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