GSM peak phase error - help

I found that the phone has peak phase error and switching spectrum fail under low voltage (3.4V). It happend at maximum power level. I have checked the PA output matching, it's already very "matched". Actually I have tried to tune the output matching but no effect on this problem.

any comment?

I think you maybe you need to tune the PA ramping profile ,may be the PA open or close too early or too late cause the Phase error and switching .

Hello,

Are you sure that your PA is not "saturated". (keep increasing the Vcontrol, do the output power increase?).
Regards.

I tried. the switching come from ramp down. I tried to tune but it just has little effect.

Reduce the PA output power would help, but it just marginal pass on switching spectrum.

it is fail on +400kHz. switching suddenly increase sharply when voltage below 3.7V. From 4.2V to 3.8V, all test item are pass and with a lot margin.

I feel so depressed....

Added after 3 minutes:

I forgot to say thank you for yours help. thanks

For me this problem sound to be a poor layout design.

At low voltage and high power the mobile charge the highest current from battery or power supply.

High peak currents during the burst traveling thin traces could make to fail the Peak Phase Error test.

hello every body. I have proplem about peak phase. My mobile design have peak phase > 20° and phase of bit 0 usually > 20° and bit 1->147 usually 2°-3°. i try to control every thing but it not good. Can you help me, as soon as ? thanks you every body .

Sometimes are problems with shield. Typically single GSM PCB doesn't work without shielding, big error and so on. But WiFi PCB s works.