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Why do some transmitter chain designs adopt a stand-alone GSM PA ????

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criterion456

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Hi, from the following link :
https://datasheet.octopart.com/SKY77629-13-Skyworks-Solutions-datasheet-16052582.pdf

A MMPA (MultiMode MultiBand Power Amplifier) can cover GSM / WCDMA / LTE

Nevertheless, some designs adopt a stand-alone PA for GSM. As the photo below :

GSM Stand-alone PA.JPG

The design increases cost and PCB placement area.
I don’t know what the benefit and consideration are.

My opinion is that WCDMA / LTE need APT(Avearage Power Tracking) or ET (Envelope Tracking), but GSM doesn’t. But I am not sure it is correct or not.

Would you please tell me the reason ??

Thanks a lot~!!
 

Maybe transceiver designed to work only in switching mode and not simultaneous mode. Or it works simultaneous in two bands with separate PAs and antennas. You did not mention how antennas arranged after PAs, maybe it will give some idea.
 

Your assumption is right. If the system support ET, then GSM PA will be separate, because ET is not used in GSM mobile PAs.
 

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