Rf Synthesizer; Front End Module Control - LG GS290 Service Manual

3. TECHNICAL BRIEF

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 (OLGA ). To overcome the
statistical 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, 1900 MHz) and operates at double or four times transmit or receive frequency. To cover the wide
frequency range the VCO is automatically aligned by a binary automatic band selection (BABS) before each
synthesizer startup.
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Only for training and service purposes

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
VC1 (FE1) VC2 (FE2)
GSM850 / 900_TX H L
GSM 1800 / 1900_ TX L H
GSM850 / 900_RX L L
GSM 1800 / 1900_ RX L L
ANT500
SW500
KMS-518_P
G1
R510
R501
A C524
C
0
22p G2 22p
L501
C539
C519 C510
100n
DNI
DNI 0.5p
Figure 27 FEM schematic
Copyright © 2010 LG Electronics. Inc. All right reserved. - 59 -
Only for training and service purposes
3. TECHNICAL BRIEF
CI:$0.05(CMOS->PIN)
R502 100
VC1
R504 100
VC2
C503 C508
47p 47p
FL500
ANT LMSP43NA-782
17
LGE Internal Use Only