Only For Training And Service Purposes - LG TU550 Service Manual

3. TECHNICAL BRIEF
3.5.9 GSM band Rx RF filter (FL100, FL101, FL102, FL103)
FL100 - B7845 869 ~ 894MHz GSM850 Rx RF filter
FL101 - B7851 1930 ~ 1990MHz PCS1900 Rx RF filter
FL102- B7837 880.2~959.8MHz GSM 900 Rx RF filter
FL103 - B7844 1805 ~1880MHz DCS1800 Rx RF filter
The GSM mode RF filters are located before their LNAs, so their insertion losses are extremely critical
(1.5 dB typical). Other important parameters are:
• Out-of-band rejection or attenuation levels
- 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.
- Frequencies of particular concern . bands known to include other wireless transmitters that may
deliver significant power levels to the receiver input.
- GSM band receivers operate while the handset transmitters are off so there are no Tx-band
leakage attenuation requirements.
• Phase and amplitude balance - the UMTS discussion presented above applies for GSM bands as
well. See the data sheet for specific values. Of course, passband ripple and return loss are still
important in all cases for the same reasons explained in the antenna switch module and duplexer
sections.
3.5.10 VCTCXO (X102 : TG-5001LA-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
MSM6275 IC. The 6250-series chipset requires a 19.2 MHz nominal VCTCXO frequency. The
oscillator frequency is controlled by the MSM6275'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