Only For Training And Service Purposes - LG L704I Service Manual

3.5.5 UMTS Rx RF filter (FL105, FL106)
FL33 - EFCH881MTDA 869 ~ 894MHz FL25 - SAFEB2G14FA0F0 2110 ~ 2170MHz An RF filter is
located between the UMTS LNA and mixer. Insertion loss is important, but not as critical as losses
before the LNA. The most important parameters of this component include:
■ Out-of-band rejection or attenuation levels, usually specified to meet these conditions:
❑ Far out-of-band signals - ranging from DC up to the first band of particular concern and from the
last band of particular concern to beyond three times the highest passband frequency.
❑ Tx-band leakage - the transmitter channel power, although attenuated by the duplexer, still
presents a cross-modulation threat in combination with Rx-band jammers. The RF filter must
provide rejection of this Tx-band leakage.
❑ Other frequencies of particular concern . bands known to include other wireless transmitters that
may deliver significant power levels to the receiver input.
■ Phase and amplitude balance - the ZIF architecture requires well-balanced differential inputs to the
RFR6275 IC. This is accomplished by the RF filter which takes a single-ended output from the
RFR6275 IC and provides differential outputs having nominal 180° phase separation. Phase and/or
amplitude imbalance causes degraded common-mode rejection and second-order nonlinearity, so
their requirements are specified jointly.
❑ ± 3 degrees and ± 1 dB
❑ -12 to + 3 degrees and ± 0.7 dB
3.5.6 VCTCXO (X4 : TG-5010LH-19.2MHz)
The Voltage Controlled Temperature Compensated Crystal Oscillator (VCTCXO) provides the
reference frequency for all RFIC synthesizers as well as clock generation functions within the
MSM6280 IC. The oscillator frequency is controlled by the MSM6280's TRK_LO_ADJ pulse density
modulated signal in the same manner as the transmit gain control.
The filtered PDM signal results in an analog control signal into the VCTCXO tuning port whose voltage
is directly proportional to the density of the digital bit stream. The MSM device varies the pulse density
to change the analog control voltage that sets the oscillator frequency - all within a feedback control
loop that minimizes handset frequency drift relative to the network.
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Only for training and service purposes

3. TECHNICAL BRIEF
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LGE Internal Use Only