Trouble Shooting Guide, Advanced
4/00021-3/FEA 209 544/25 C
Ericsson Mobile Communications AB
53(78)
16 Calibration Power Level
16.1 Introduction
In the EGSM 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 GSM1800 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,
thepowerlevelsofthephonehavetobeasthebasestationexpect.
This means that the power levels of the phone have to be calibrated to be accurate enough.
Fig. 16.1 shows a very simplified schematic of the power regulation.
Fig. 16.1
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
N500.
The output power POWLEV of the DAC let the power regulation of the radio know how
large the power should be.
N700 uses POWLEV to create the control voltage PRAREG 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
V400.
The signals are called PASENSE+ and PASENSE-.
Table 16.1 (EGSM900) and Table 16.2 (GSM1800) shows the default DAC values and the
output power goal of the calibration.
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