User Guide

CCS Technical Documentation System Module LG4 and Grip Module LS4
Issue 2 11/02 ¤Nokia Corporation Page 47
Figure 26: Gain control of GSM1800
AFC function
The AFC is used to lock the transceivers clock to frequency of the base station. The AFC
voltage is generated in baseband using an 11 bit DAC where an RC-filter is placed on the
AFC control line to reduce the noise from the converter. The settling time requirement
-100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0
LNA gain = +19dB ( GSM1800 ) LNA gain = -11dB ( GSM1800 )
DtoS gain = ? dB DtoS gain = ? dB
Accurate gain control region
ADC input
voltage
[ mV
p-t-p ]
RF signal
[ dBm ]
+
4
6
d
B
+
3
6
d
B
+
2
6
d
B
+
1
6
d
B
+6dB
-
4
d
B
+
1
6dB
+
6
dB
-
4
d
B
-110
Accurate RSSI requirment range
19+46=65
19+36=55
19+26=45
19+16=35
19+6=25
19-4=15
-11+16=5
-11+6=--5
-11-4=-15
Receiver chain
gain
[ dB ]
65
55
45
35
25
15
5
-5
-15
RF signal
[ dBm ]
-110 -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0