Rf Synthesizer; Dcxo - LG KF350 Service Manual

In GMSK mode, the PA is in saturated high efficiency mode and is controlled via its VAPC pin directly
by the baseband ramping DAC. In this way both up- / down-ramping and output power level are set. In
8PSK mode, the ramping functionality is assured by an on-chip ramping generator, whereas output
power is controlled by the PGA's as described above.

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.

3.20 DCXO

The SMARTiPM contains a fully integrated 26MHz digitally controlled crystal oscillator (DCXO) with
three outputs for the system clock, one output for the GSM baseband and two additional for other
subsystems (GPS, Bluetooth, etc.).The only external part of the oscillator is the crystal itself. The
frequency tuning is performed along the selected subrange by programming the frequency control
word (XO_TUNE) via the three wire bus ("3Wbus")
Copyright © 2008 LG Electronics. Inc. All right reserved.
Only for training and service purposes
X400 NX3225SA
4
3
GND2 HOT2
1 GND1 2
HOT1
26MHz
Figure 28 DCXO Schematic
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3. TECHNICAL BRIEF
LGE Internal Use Only