Nokia 2600 服务手册
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Nokia Customer Care
48
COMPANY CONFIDENTIAL
ISSUE 1 09/2004
Copyright © 2004 Nokia. All Rights Reserved.
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Synthesizer
There is only one PLL synthesizer generating Local Oscillator frequencies for both RX and TX
in both bands ( PCN and EGSM). The VCO frequency is divided by 2 for PCN operation or by
4 for EGSM operation inside the Mjoelner IC.
in both bands ( PCN and EGSM). The VCO frequency is divided by 2 for PCN operation or by
4 for EGSM operation inside the Mjoelner IC.
26 MHz reference oscillator ( VCXO )
The 26 MHz oscillator is located in the Mjoelner IC (N600). The coarse frequency for this oscil-
lator is set by an external crystal (B600). The reference oscillator is used as a reference fre-
quency for the PLL synthesizer and as the system clock for BaseBand. The 26MHz signal is
divided by 2 to achieve 13MHz inside the UPP IC (D400).
lator is set by an external crystal (B600). The reference oscillator is used as a reference fre-
quency for the PLL synthesizer and as the system clock for BaseBand. The 26MHz signal is
divided by 2 to achieve 13MHz inside the UPP IC (D400).
The 26 MHz signal from the VCXO can be measured by probing R425 (must be measured on
the UPP side of R425 i.e. the end not
the UPP side of R425 i.e. the end not
connected to C425). The level at this point is approx.
700mVpp. Frequency of this oscillator is adjusted by changing the AFC-register inside the
Mjoelner IC. This is done via the Mjoelner serial interface.
Mjoelner IC. This is done via the Mjoelner serial interface.
Example Signal Measured at VCXO output (R425)
Figure 45: VCXO 26 MHz waveform
VCO
The VCO is an ASIC with all the frequency determining parts inside.
In order to reduce the requirements of the tuning voltage and coverage of the VCO, the VCO
core is composed of four VCOs in parallel. This VCO circuit enables a very wide tun-ing range
of 3.4 - 4.0 GHz .
core is composed of four VCOs in parallel. This VCO circuit enables a very wide tun-ing range
of 3.4 - 4.0 GHz .