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How to design asymmetrical Doherty power amplifier?

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slienteyes

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doherty power amplifier

How to design asymmetrical Doherty power amplifier? Using uneven power splitter could be one way. question is how to define which path have more power, main amplifier path or peak amplifier path?
Other way is to use different LDMOS transistor, do you have some suggestion on it?

Besides, how to design three-way doherty power amplifier?
 

asymmetrical doherty

You must make sure the change of output impedence of two branches as input power increasing. Then decide which one get more power based on the impedence changing of main and peak amplifier (2Zopt->Zopt/2)
 

inverted doherty amplifier

He means which type doherty you choose, regular or inverted, right?
 

doherty amplifier design

In my view different LDMOS transistors for Doherty amplifier will lead to more losses in power combining over broad band.
It may also lead critical in bias design.
the below link gives you on N- way ans explains on 3 way too.
**broken link removed**
 

how to design a doherty amplifier

I recommend this reference

S. Bousnina, “Analysis and design of high efficiency variable conduction angle Doherty amplifier,” ITE antenna & propagation journal, vol. 3, no. 3, pp. 416-425, April 2009.

It shows how to design an asymmetrical Doherty amplifier, how to bias the main and auxiliary amplifier, and how much power is expected from each asymmetrical Doherty amplifier configuration. The same principle can be extended to the design of three-way Doherty amplifier.

Regarding the LDMOS devices, it is better to use transistors with low output parasitics (including package capacitance). That way it will be easier to reproduce the resistive load pulling effect in the Doherty amplifier.
 

asymmetrical doherty amplifier

Asymmetrical doherty amplifier can be designed by simultaneously adjusting the load of the main amplifier at low drive level simultaneously with the bias of the auxiliary amplifier and the ratio of the power splitting at the input.
Theoretical analysis and simulations with a large signal model can determine the ration of the power splitting.
I went through the referenced paper and it seems that presented analysis can be extended to determine the ration of the power splitting. The paper also consider for the conduction angle of the auxiliary amplifier since it is biased class C.
I think it also possible to derive similar equations for bipolar device.
 

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