Afc Function; Receiver Blocks; Rx Interstage Filter; 1St Mixer In Crfu_1A - Nokia NSE-6 SERIES Service Manual

PAMS
Technical Documentation

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 frequency
accuracy. The VCTCXO–module requires also 5 ms to settle into final
frequency. Amplitude rises into full swing in 1 ... 2 ms, but frequency set-
tling 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
Original 08/98
Min. Typ.
935 – 960
Min. Typ./ Max.
Nom.
2.7 2.8
935
1006
71
10 k
min.
–20
System Module
Max. Unit
MHz
3.3 dB
+15 dBm
Unit/Notes
2.85 V
960 MHz
1031 MHz
MHz
ohm
typ. max.
+75
71
8.5
Page 3 – 55
NSE–6
unit
deg.C
MHz
dB