Lo Generation And Distribution Circuits; Only For Training And Service Purposes - LG KE990 - Viewty Cell Phone 100 MB Service Manual

3. TECHNICAL BRIEF

3.3 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 band upconverters and
downconverters; with the help of these LO generation and distribution circuits, true zero-IF architecture
is employed in all GSM 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
RTR6235 IC. The synthesizer (PLL1) creates the transceiver LOs that support four GSM band
receivers and transmitters including: GSM850, EGSM900, DCS1800, and PCS1900. An external
TCXO input signal is required to provide the synthesizer frequency reference to which the PLL is
phase and frequency locked. The RTR6235 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 RTR6235 has the advantages of
more flexible loop bandwidth control, fast lock time, and low-integrated phase error
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Only for training and service purposes