LG U8210, Руководство по обслуживанию, Страница: 36 / 231

3. TECHNICAL BRIEF
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3.5.9 GSM band Rx RF filter (FL201, FL202, FL203)
FL201 - B7037 925 ~ 960MHz EGSM Rx RF filter
FL202 - B7844 1805 ~1880MHz DCS1800 Rx RF filter
FL203 - B7846 1930 ~ 1990MHz PCS1900 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 dash 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 (U206 : 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
MSM6250 IC. The 6250-series chipset requires a 19.2 MHz nominal VCTCXO frequency . The
oscillator frequency is controlled by the MSM6250’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.
3.5.11 UMTS Rx VCO (U208 : MQL302A1G71)
The UMTS Rx CH VCO is a key component within its phase-locked loop; VCO performance directlry
impacts PLL and receiver performance.
When the phone is not in the UMTS mode the unused VCO must be turned off by UHF_VCO_EN logic
signal from MSM6250. Using only the external UMTS_RX_VCO signal, the LO generation and
distribution circuits create the necessary LO signals for the quadrature downconverter.
3.5.12 Bluetooth (U406 : RB06A, ANT400 : KFBA090025020AA )
The MSM6250 includes BT baseband embedded BT 1.1 compliant baseband core, so the other
bluetooth components are an bluetooth RF module and Antenna. Figure 3.5.12-1 shows the bluetooth
system architecture in the U8210.