Reason for Phase Error reported in a GSM handset?

[westrice2002]

phase error

hello, everybody. thanks for your help.

There is a PhaseError issue reported in a GSM handset. Maybe it's related about the modulator or the phase noise of the RF synthesizer. But they are all located inside a chipset. Is there any other possible reason?

 

[artem]

I do not know where is the phase error is reported , but sometimes it could be the case due to synchronization in operator networks . There is BCCH (broadcast control channel ) where is the SCH - synchronization channel is seated v. if there are 2 operators and there is no synchronization between their physical channels on air interface I have seen the case where mobile locked due to different unsynchronized frequences . SCH get synschronization
from digital transmission coming to the base stations from BSC . I did not clarify the cause of the problem but this could either be within mobile and network as well .

 

[ttrf]

phase error

group delay of filter, Sideband Suppression and carrier Suppression

 

[westrice2002]

Thanks for your reply, artem and ttrf.

The test is performed with CMU in a shielding room. In the transmit path, there is no discrete filters, and there is no enough test points to test the Sideband suppression and carrier suppression.

How to solve the problem?What's the main possible contributors? Any suggestions? Thanks a lot.

 

[martinthorn]

Hi,
Perhaps you have fixed your problem, but if not here's a few ideas.
There are many possible causes for poor phase error in a GSM handset,
here are just some I have come across :

-TX VCO pulling due to RF power from PA : poor layout of RF
-faulty PA device
-PA power control fault/noise
-faulty TX VCO : spurious on output
-misaligned/faulty IQ modulator
-IQ data corrupted/incorrect/noisy
-RF feedback to device regulators/supplies
-faulty PLL components (loop filter caps correct value ?)
-TX PA outputting too much power ?
-VCXO faulty : too noisy, adds to PLL noise
-and others.. such as smd faults on asic balls or shields

without more details of the GSM handset in question it's difficult to
be anymore specific...

Martin