User Guide

PAMS

Technical Documentation

NSE–8/9

System Module

Page 2– 77

Issue 1 07/99

To preserve the stability of the loop a resistor is included for phase

compensation. Other filter components are for sideband rejection.

The dividers are controlled via the serial bus. SDATA is for data, SCLK is

the serial clock for the bus and SENA1 is a latch enable, which enables

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

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

diplexer that has one common antenna input/output is used. The selection

between GSM900 and GSM1800 operation modes in the CRFU3 is done

with the band selection signal (BAND_SEL) from the MAD in baseband.