Rf Synthesizer; Front End Module Control - LG GM360i Service Manual

3.19 RF synthesizer

The transceiver contains a fractional-N sigma-delta synthesizer for the frequency synthesis in the RX operation
mode. For TX operation mode the fractional-N sigma-delta synthesizer is used as Sigma-Delta modulation loop
to process the phase/frequency signal. The 26MHz reference signal is provided by the internal crystal oscillator.
This frequency serves as comparison frequency of the phase detector and as clock frequency for all digital
circuitry.The divider in the feedback path of the synthesizer is carried out as a multi-modulus divider (MMD). The
loop filter is fully integrated and the loop bandwidth is about 100 kHz to allow the transfer of the phase
modulation. The loop bandwidth is automatically adjusted prior to each slot (OLGA2). To overcome the statistical

3.20 Front End Module control

spread of the loop filter element values an automatic loop filter adjustment (ALFA) is performed before each
synthesizer startup. The fully integrated quad-band VCO is designed for the four GSM bands (850, 900, 1800,
Implemented in the S-Gold3 (FL500) are two outputs which are VC1, VC2 for direct control of front end modules
1900 MHz) and operates at double or four times transmit or receive frequency. To cover the wide frequency
with two logic input pins to select RX and TX mode as well as low and high band operation..
range the VCO is automatically aligned by a binary automatic band selection (BABS) before each synthesizer
startup.
Table 8 FEM Control Logic
3.20 Front End Module control
Implemented in the S-Gold3 (FL500) are two outputs which are VC1, VC2 for direct control of front end modules
with two logic input pins to select RX and TX mode as well as low and high band operation..
Table 8 FEM Control Logic
GSM 1800 / 1900_ TX
ANT504
GSM850 / 900_RX
GSM 1800 / 1900_ RX
C10 4.7pF C9 82pF
C530
C537
18n 1.8p
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LG Electronics
Only for training and service purposes
VC1 (FE1) VC2 (FE2)
L H
L L
L L
SW501
C542
2
ANT COMMON
1
100pF
G3 G4
3 4 L502 C521
DNI DNI
Figure 27 FEM schematic
Figure 27 FEM schematic
61/147
FL500
ANT
17
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3. TECHNICAL BRIEF
R505 100ohms
VC1
(FROM Transceiver)
R506 100ohms
VC2
(FROM Transceiver)
C525 C528
47pF 47pF
LGE Internal Use Only
LGE Property