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8 Calibration of Power Level
8.1
Introduction
In the GSM 900 system is it possible for a phone to transmit with 15 different power levels,
from 33 dBm, power level 5 to 5 dBm, power level 19.
In the GSM 1800 system is it possible for a phone to transmit with 16 different power levels,
from 30 dBm, power level 0 to 0 dBm, power level 15.
It is best to transmit at as low output power as possible, but with maintained transfer quality, in
order to e.g. save current in the battery and restrict the disturbances.
The base station evaluates the transfer quality and informs the phone when to change the output
power.
For the base station to be able to regulate the output power of the phone in a satisfying way, the
power levels of the phone have to be as the base station expect.
This means that the power levels of the phone have to be calibrated to be accurate enough.
Figure below shows a very simplified schematic of the power regulation Fig.8.1
The calibrated DAC values are stored in the EEPROM.
When the base station orders the phone to transmit at a certain power level, is the DAC value for
the current power level taken from the EEPROM and sent to the Power level-DAC in N800.
The output power POWLEV of the DAC let the power regulation of the radio know how large
the power should be.
N450 uses POWLEV to create the control voltage VREG with Offset level and Full Power
level, it regulates the amplification of the power amplifier.
The regulation is fed back by measuring the current consumption of the power amplifier using
R413.
The signal is called VSENSE.
4/00021-3/FEA 209 544/18 B
Fig.8.1
Trouble Shooting Guide, Advanced
37(121)
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