26 Mhz Reference Oscillator (Vcxo); Vco; Fault Finding Chart For Pll Synthesizer - Nokia 616 Service Manual

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26 MHz reference oscillator ( VCXO )
The 26 MHz reference oscillator (VCXO) is part of Mjoelner RF-ASIC (N601). It requires
only an external 26 MHz Xtal (B601) as external circuitry. The reference oscillator has
three functions:
• Reference frequency for the PLL synthesizer.
• System clock for BB (RFClk_I = 26 MHz).
• 26 MHz Reference clock (LPRFClk_I) for Bluetooth Module (V130) via buffer
V601.
For a successful initial synchronization, the 26MHz frequency of the VCXO must be cali-
brated accurately. Therefore, a VCXO-calibration (cal) value is written via the serial
Bus into the RefOSCCAL register of Mjoelner and an additional bit in the RefOSCCntl
register of the Mjoelner. That is necessary for the rough calibration of the VCXO. The
VCXO is fine tuned by programming the AFC value via the serial bus of Mjoelner. The
necessary AFC value is written into the RefOSCAFC register inside the Mjoelner.

VCO

The VCO has to generate frequencies in the range from 3420MHz to 3840MHz for the
PLL. The frequency of the VCO signal is divided by 2 or by 4 in Mjoelner RF-ASIC. Gener-
ate the frequency of all channels in EGSM900, GSM1800 (both RX and TX). Frequency of
the VCO is controlled by DC voltage (Vc) the output of the PLL loop filter. Range of Vc
when PLL is operating is 0.7V– 3.8V. Typical tuning sensitivity of the VCO is 240MHz/V.
Even if PLL is not working (Vc out of range) there should be a frequency at the output of
the VCO, between 3 and 4 GHz (if the VCO itself is ok).

Fault finding chart for PLL Synthesizer

Setup with
Band: GSM 900
Mode: RX Continuous
Channel: 37
Spectrumanalyzer
VCO out (G701) No
f = 3769.6 MHz
VCO
U =2.3..2.8V
tune
Yes
Oscilloscope
Bluetooth Clockbuffer
No
(R601 LPRFCLK_I)
26MHz app. 0.6Vpp
Yes
PLL Block is functional
Issue 2.0 Mar/2005
Company Confidential
BB not working
PLL Synthesiser Fault finding Tree
because 26MHz
missing.
Oscilloscope
VCXO Supply (C607)
Yes
(
VR3=2.78V, VIO=1.8V
VREF1=1.35V)
No
Check supply filter components
Check BB, and Software
Phone not in function
Check Bluetooth
Clockbuffer
R601,R602,R603,
V601,C602
(For a failure free working of BB the 26MHz clock is necessary!!!)
If the 26MHz clock isn´t work please check first the necessary voltages
VR3;VIO and VREF01. This can be checked after power on for a time of
about 32sec. After that time the voltages a going down.)
Copyright © 2005 Nokia Corporation.
Company Confidential
TF4 Technical Information
Oscilloscope
VCXO output
Yes
(R425 RFCLK
26MHz,app.0.8Vpp
No
Check supply filter components
Check UEM, and Software
check R618; C425
B601+Mjoelner Phone not in function
Loop filter components?
If ok change Mjoelner
Yes
Wrong writing on RFBus
(see BB part)
TFE-4/RV-1
Oscilloscope VCO supply
(
VR7 = 2.78V, VR5=2.78V)
VR1A=4.7V
No
Yes
Spectrumanalyzer
VCO out (G701 out)
Some signal 3-4 GHz
No
Change VCO G701
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