Afc Function - Nokia NSE–3 SERIES Service Manual

NSE–3
System Module

AFC function

AFC is used to lock the transceivers clock to frequency of the base sta-
tion. AFC–voltage is generated in COBBA with 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. AFC tracks
base station frequency continously, so transceiver has got a stable fre-
quency, because changes in VCTCXO–output don't occur so fast ( tem-
perature ). 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 fre-
quency accuracy. The VCTCXO–module requires also 5 ms to settle into
final frequency. Amplitude rises into full swing in 1 ... 2 ms, but frequency
settling time is higher so this oscillator must be powered up early enough.
Receiver blocks
RX interstage filter
Parameter
Passband
Insertion loss
Maximum drive level
1st mixer in CRFU_1a
Parameter
Supply voltage
RX frequency range
LO frequency range
IF frequency
Output resistance (balanced)
1st IF–filter
Parameter
Operating temperature range
Center frequency , fo
Maximum ins. loss at 1dBBW
Page 3 – 56
Min. Typ.
935 – 960
Min. Typ./ Max.
Nom.
2.7 2.8
935
1006
71
10 k
min.
–20
Technical Documentation
Max. Unit
MHz
3.8 dB
+10 dBm
Unit/Notes
2.85 V
960 MHz
1031 MHz
MHz
ohm
typ. max.
+75
71
11
Original 11/97
PAMS
unit
deg.C
MHz
dB