Lo Generation And Distribution Circuits; Off-Chip Rf Components - LG KB770 Service Manual

3. TECHNICAL BRIEF

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
RTR6275 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 RTR6275 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 RTR6275 has the advantages of more flexible loop bandwidth control,
fast lock time, and low-integrated phase error

3.5 Off-chip RF Components

3.5.1 Front-End Module(FL100 : LMSP4LMA-573TEMP)
This equipment uses a single antenna to support all handset operating modes, with an antenna switch
module select the operating frequency and band. UMTS operation requires simultaneous reception and
transmission, so the UMTS Rx/Tx connection is routed to a duplexer that separates receive and transmit
signals. The active connection is MSM-selected by three control lines (GPIO[9], GPIO[10], GPIO[11],
GPIO[12]). These GPIOs are programmed to be ANT_SEL0, ANT_SEL1, ANT_SEL2, ANT_SEL3
respectively.
LGE Internal Use Only
Table 3.5.1 Antenna Switch Module Control logic
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