About AM-PM characteristic of LDMOS power amplifier.

Has anyone measured the AM-PM characteristic of a LDMOS power amplifier?
It's positive or negative？

I studied some papers about predistortion. I found that some linearizers in some papers have positive AM-PM characteristic while others have negative AM-PM characteristic. I feel strange.

I want to design a series predistortion linearizer using Schottky diode to improve the IM3 and IM5 performance of PA based on MRF9060 LDMOS transistor from Freescale. Does anyone have experience on this issue? Can you give me some suggestions or some papers?

Thank you.

you can use network analyzer to sweep the power and watch the phase. The curve is the AM-PM curve.

Hi, foxgan:
Of course I know I can measure the AM-PM curve using network analyzer. But right now, it's not convenient for me to do that. So I want to ask for someone's experience.

Thank you for your information.