Nokia 9110 Service Manual
PAMS
Technical Documentation
RAE–2
BS8_RF
Page 3 – 17
Original 02/99
required. Remaining 10 dB is for gain variations in RX–chain ( for calibra-
tion )
tion )
Below –95 dBm RF–levels, output level of the receiver drops dB by dB.
At –95 dBm level output of the receiver gives 50 mVpp. This is the target
value for DSP. Below this it drops down to ca. 9 mVpp @ –110 dBm RF–
level.
At –95 dBm level output of the receiver gives 50 mVpp. This is the target
value for DSP. Below this it drops down to ca. 9 mVpp @ –110 dBm RF–
level.
This strategy is chosen because we have to roll off the AGC in PLUSSA
early enough, that it won’t saturate in selectivity tests. Also we can’t start
too early, then we will sacrifice the signal to noise ratio and it would re-
quire more accurate AGC dynamic range. 50 mVpp target level is set,
because RX–DAC will saturate at 1.4 Vpp. This over 28 dB headroom is
required to have margin for +/– 200 kHz faded adjacent channel ( ca. 19
dB ) and extra 9 dB for pre–monitoring.
early enough, that it won’t saturate in selectivity tests. Also we can’t start
too early, then we will sacrifice the signal to noise ratio and it would re-
quire more accurate AGC dynamic range. 50 mVpp target level is set,
because RX–DAC will saturate at 1.4 Vpp. This over 28 dB headroom is
required to have margin for +/– 200 kHz faded adjacent channel ( ca. 19
dB ) and extra 9 dB for pre–monitoring.
Production calibration is done with two RF–levels, LNA gain step is not
calibrated. The gain changes in the receiver are taken off from the dy-
namic range of accurate AGC. Variable gain stage in SUMMA is designed
in a way, that it is capable of compensating itself, there is good enough
margin in AGC.
calibrated. The gain changes in the receiver are taken off from the dy-
namic range of accurate AGC. Variable gain stage in SUMMA is designed
in a way, that it is capable of compensating itself, there is good enough
margin in AGC.
AFC function
AFC is used to lock the transceivers clock to the frequency of the base
station.
station.
AFC–voltage is generated in the COBBA with a 11 bit AD–converter.
There is a RC–filter in AFC control line to reduce the noise from the con-
verter. Settling time requirement for the RC–network comes from signal-
ling, how often PSW ( pure sine wave ) slots occur. They are repeated af-
ter 10 frames , meaning that there is PSW in every 46 ms.
There is a RC–filter in AFC control line to reduce the noise from the con-
verter. Settling time requirement for the RC–network comes from signal-
ling, how often PSW ( pure sine wave ) slots occur. They are repeated af-
ter 10 frames , meaning that there is PSW in every 46 ms.
AFC tracks the base station frequency continuously, so the transceiver
has got a stable frequency, because changes in the VCTCXO–output
don’t occur so fast ( temperature ).
has got a stable frequency, because changes in the VCTCXO–output
don’t occur so fast ( temperature ).
Settling time requirement comes also from the start up–time allowed.
When transceiver is in sleep mode and ”wakes” up to receive mode ,
there is only about 5 ms for the AFC–voltage to settle. When the first
burst comes in system clock has to be settled into +/– 0.1 ppm frequency
accuracy. Settling time requirement comes also from the start up–time al-
lowed. When transceiver is in sleep mode and ”wakes” up to receive
mode , there is only about 5 ms for the AFC–voltage to settle. When the
first burst comes in system clock has to be settled into +/– 0.1 ppm fre-
quency accuracy.
When transceiver is in sleep mode and ”wakes” up to receive mode ,
there is only about 5 ms for the AFC–voltage to settle. When the first
burst comes in system clock has to be settled into +/– 0.1 ppm frequency
accuracy. Settling time requirement comes also from the start up–time al-
lowed. When transceiver is in sleep mode and ”wakes” up to receive
mode , there is only about 5 ms for the AFC–voltage to settle. When the
first burst comes in system clock has to be settled into +/– 0.1 ppm fre-
quency accuracy.
The VCTCXO–module requires also 5 ms to settle into final frequency.
Amplitude rises into full swing in 1 ... 3 ms, but frequency settling time is
longer so this oscillator must be powered up early enough.
Amplitude rises into full swing in 1 ... 3 ms, but frequency settling time is
longer so this oscillator must be powered up early enough.