Only For Training And Service Purposes - LG GM310 Service Manual

4.2.3 GSM RF Synthesizer
The SMARTi 3GE 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 spread of the loopfilter element values an automatic loopfilter 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.
4.2.4 Reference Oscillator
The SMARTi 3GE comprises three 26MHz reference frequency outputs for the GSM baseband, for the
3G RF and for other subsystems (GPS, Bluetooth, etc.) as well as an reference frequency input for
application of an external VCXO module.
4.2.5 Front End Module Control
Implemented in the SMARTi 3GE are two outputs for direct control of GSM front end modules with two
logic input pins to select RX- and TX-mode as well as low- and highband operation.
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Only for training and service purposes

4. RF Circuit Technical Brief
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