Source pull---Power Amplifier

[jayce3390]

Hi all,

I don't really understand the need of source pull measurement on the load pull bench.
You can perform a load pull measurement on PA using a 50 ohms source impedance on the bench, using only one tuner at the PA output.
I think that will not distort the results, but you will need more input power due to reflect coefficient.


What do you think about it?

 

[madengr]

I think that will not distort the results, but you will need more input power due to reflect coefficient.

Yes that is true, however remember that a FET is modeled as voltage controlled current source. The shape of the gate voltage waveform affects the drain current. That is why the peak output power does not always coincide with the best input return loss. You match the gate to achieve the highest output power (or gain), not the best return loss as one would expect with a linear circuit.

 

[jayce3390]

Ok, On source pull bench measurement it's necessary to set source impedance which provides best output power rather than corresponding to best IRL.
If you put the corresponding source impedance and you perform a load pull measurement, does it impact on founded load impedances?


Thanks in advance

 

[madengr]

A little, however the effect of load on the source is more pronounced. Experiment with some tuners and transistors and you will see the effect.