Afc; Software Compensations; Power Levels (Txc) Vs. Channel; Modulator Output Level - Nokia NSB-5 Series Technical Documentation Manual

NSB-5
System Module
to desired value (50mVp–p). This is accomplished in DSP by measuring the receive IQ
level after the selectivity filtering (IF–filters, SD–converter and FIR–filter in DSP). This
results in an AGC dynamic range of 50 dB with the remaining 7 dB for gain variations in
RX–chain (for calibration). For RF levels below –95 dBm, the output level of the receiver
drops dB by dB with a level of 7.1 mVp–p @ –110 dBm for GSM1900.
This strategy is chosen because it is necessary to roll off the AGC in SUMMA early so that
the signal is not saturated in selectivity tests but cannot roll off too early as this will sac-
rifice the signal to noise ratio, thus requiring a larger AGC dynamic range. The 50 mVpp
target level is set, because the RX–DAC in COBBA_GJP will saturate at 1.4 Vpp. This re-
sults in over 28 dB of headroom which is required for the +/– 200 kHz faded adjacent
channel (approximately 19 dB) and extra 9 dB for pre– monitoring.

AFC

The AFC is used to lock the MS clock to the frequency of the BS. AFC voltage is gener-
ated in COBBA_GJP with an 11 bit ADC. This voltage then controls the center frequency
of the 13 MHz VCTCXO module.

Software Compensations

Power Levels (TXC) vs. Channel

Power levels are calibrated on one channel in production. Values for channels between
these tuned channels are calculated using linear interpolation.

Modulator Output Level

For optimum linearity and efficiency, the output level of the modulator is adjusted in the
production.

Power Levels vs temperature

In order to avoid the bias voltage variation of the detector diode ruining the accuracy of
the power control loop, the bias voltage of the detector is measured when no RF power is
transmitted. This voltage (DETLVL) is fed to the A/D converter in CCONT where DSP uses
this value to correct the TXC voltage.

RSSI

Signal strength RSSI vs. input signal is calibrated in production, but RSSI vs. channel is
compensated by software. If DETLVL (A/D) is used as a temperature sensor to correct for
RX variations over temperature, the diode characteristics are 1.2mV/C.

TX power range

If COBBA_GJP does meet specifications, it will be necessary to divide the power levels
into two ranges. One range will be between power level 0 to 10 (lets call this the HI
range) with the other range between 11 and 15 (lets call this the LO range) . NOTE: at
this time the exact range is unknown. One of MAD2_WD1 DSPGenOut pins will be used.
The TX power control range is divided into two regions for reasons of linearity in the
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PAMS Technical Documentation
Issue 1 03/01