Synthesizer; 26 Mhz Reference Oscillator (Vcxo ); Vco - Nokia RM-4 Troubleshooting Instructions

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RM-4/RM-5

Troubleshooting Instructions

CCS Technical Documentation

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.

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).

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 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.

Example Signal Measured at VCXO output (R425)

Figure 20: VCXO 26 MHz waveform

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 tuning range

of 3.4 - 4.0 GHz .

ISSUE 1 02/2004

COMPANY CONFIDENTIAL

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Rm-5