Nokia Mobile Phones NSE-5 Series, Руководство по обслуживанию

Страница: 69 / 327

PAMS
Technical Documentation
NSE–5
System Module
Page 2 – 55
Issue 1 07/99
storing of new data into the dividers. The UHF-synthesizer is the channel
synthesizer, so each step equals the channel spacing (200 kHz). When
GSM900 operation is active, a 200 kHz reference frequency is used for
the phase detector. For GSM1800 operation, a 100 kHz reference
frequency has to be used.
This is because the GSM1800 UHF parts use a 2GHz LO–signal, but the
UHF synthesizer is locked to a 1GHz LO–signal, which is derived by
dividing the 2GHz LO–signal by two.
Except for the VHF–VCO the VHF PLL is located in the SUMMA. It is
common for both systems like the UHF PLL. The part in the SUMMA
includes a 16/17 (P/P+1) dual modulus prescaler, an N- and A-dividers, a
reference divider, a phase detector and a charge pump for the loop filter.
The VHF–VCO is running at 464MHz. The operation of the VHF PLL is
identical to that of the UHF PLL, except for the use of the prescaler in the
CRFU3. The used reference frequency is 333kHz.
Receiver
Figure 17. Receiver Block Diagram
The receiver is a conventional dual conversion for GSM900 and triple
conversion for GSM1800. Both receivers use upper side LO injection in
the first RF mixer, after that lower side LO injection is used. Because of
this there is no need for changing I/Q phasing in baseband when receiving
band is changed between GSM1800 and GSM900.The two receiver
chains are combined in 71 MHz IF so that they use the same RX chain
from that point down to 13MHz AD converter. Because there is only used
one external antenna connector, common for both bands, a dualband