how to measure the linearity of the included VGA in TX

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abcyin

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topology: baseband VGA->mixer->PA, only PA's output can be detected by the equipment.

But I want to measure the linearity of the variable gain amplifier, how could I do it? is there anybody who can give me some advices?

Thx in advance!
 

It depends on the 3 stages linearity: if there isn't a condition in which the overall linearity is limited by the VGA, you cannot measure it (but in this case you should not be interested in it...). Use formula for the IP3 cascade to calculate if this condition is met.
I hope it can help.

suggestion: next time ask to the designers to provide a test point at VGA output.

Mazz
 

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