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3. TECHNICAL BRIEF
The PA interface of SMARTi 3GE supports direct control of standard dual mode power amplifiers
(PA’s) which usually have a power control input VAPC and an optional bias control pin VBIAS for
efficiency enhancement. 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.
3.17.3 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 (OLGA
2
). 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.
3.17.4 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.
3.17.5 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.
LGE Internal Use Only
Copyright © 2008 LG Electronics. Inc. All right reserved.
Only for training and service purposes
