Transmitter Part - LG GD310 Service Manual

3.19. Transmitter part

The GMSK transmitter supports power class 4 for GSM850 and GSM900 as well as power class 1 for
DCS1800 and PCS1900. The digital transmitter architecture is based on a very low power fractional-N
Sigma-Delta synthesizer without any external components. The analog I/Q modulation data from the
baseband is converted to digital, filtered and transformed to polar coordinates. The phase/frequency
signal is further on processed by the Sigma-Delta modulation loop. The output of its associated VCO is
divided by four or two, respectively, and connected via an output buffer to the appropriate single ended
output pin. This configuration ensures minimum noise level. The 8PSK transmitter supports power class
E2 for GSM850 and GSM900 as well as for DCS1800 and PCS1900. The digital transmitter architecture
is based on a polar modulation architecture, where the analog modulation data (rectangular I/Q
coordinates) is converted to digital data stream and is subsequently transformed to polar coordinates by
means of a CORDIC algorithm. The resulting amplitude information is fed into a digital multiplier for
power ramping and level control. The ready processed amplitude signal is applied to a DAC followed by
a low pass filter which reconstructs the analog amplitude information. The phase signal from the
CORDIC is applied to the Sigma-Delta fractional-N modulation loop. The divided output of its associated
VCO is fed to a highly linear amplitude modulator, recombining amplitude and phase information. The
output of the amplitude modulator is connected to a single ended output RF PGA for digitally setting the
wanted transmit power. The PA interface of SMARTi-PM 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.
Copyright © 2009 LG Electronics. Inc. All right reserved.
Only for training and service purposes
Figure 30. Transmitter part block diagram
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3. Technical Brief
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