User Guide

NHL-12
Nokia Customer Care 7 - RF Description & Troubleshooting
38 COMPANY CONFIDENTIAL Issue 2 10/2004
Copyright © 2004 Nokia. All Rights Reserved.
7. Synthesizer Description and Troubleshooting
One PLL synthesizer is generating all the required frequencies for both Rx and Tx and for all
three bands (GSM850/1800/1900).
■ Frequency synthesizers
The VCO frequency is locked by a PLL (phase locked loop) into a stable frequency source giv-
en by a VCTCXO which is running at 26 MHz. The frequency of the VCTCXO is in turn locked
into the base station frequency with the help of an AFC voltage that is generated in the UEM
by an 11 bit D/A converter. The PLL is located in Helgo and it is controlled through the RFBus.
The required frequency dividers for modulator and demodulator mixers are integrated in Helgo.
Loop filter filters out the comparison pulses of the phase detector and generates a DC control
voltage to the VCO. The loop filter determines the step response of the PLL (settling time) and
contributes to the stability of the loop.
The frequency synthesizer is integrated in Helgo except for the VCTCXO, VCO, and the loop
filter.
Table 2: 26 MHz reference oscillator (VCTCXO)
Parameter Min Typ Max
Unit/
Notes
Supply voltage, Vcc 2.60 2.70 2.80 V
Current consumption, Icc 1.5 mA
Operating temperature range -30 +80 deg. C
Nominal frequency 26 MHz
Output voltage swing, Vcc=2.6V
Temp=-20...+75deg. C
(swing of the 26MHz component, a selec-
tive measurement from the spectrum)
0.8 Vpp
Load, resistance
capacitance
2
10
kohm
pF
Frequency tolerance @+25deg. C
with internal frequency tuning
no tuning
-1.0
-10
+1.0
+10
ppm
ppm
Frequency tolerance after reflow
(@+25deg. C)
-1.0 +1.0 ppm
Frequency stability vs. temperature
(ref. @+25, -20....+75deg. C)
-5.0 +5.0 ppm
Frequency stability vs. supply voltage
(2.7V +/- 100mV)
-0.2 +0.2 ppm