Carrier (main) Doherty power amplifier

[Mabrok]

Regarding the main (carrier) stage of doherty power amplifier matching network. I have done the load Pull for saturation and BO performance according to my design targets. I got two different load impedance for saturation and back-off which are 7.311+j7.596 & 7.656+j13.258 respectively. My question is how to deal with these two loads when i want to design the matching network? Which impedance should I choose in order to maintain the performance for both saturation and back-off? I have tried to take the average value of the two loads which is 7.4835+j10.427 and designed the matching network according to this impedance. Unfortunately, I could get the back-off performance as required. please advice me with this if anyone have experience with doherty power amplifier design. thanks in advanced.

 

[BigBoss]

First Impedance will be used while the Main Amplifier working standalone, the second Impedance when the Auxiliary Amplifier starts to involve..

 

[Mabrok]

First Impedance will be used while the Main Amplifier working standalone, the second Impedance when the Auxiliary Amplifier starts to involve..

Thank you. Which impedance have to use while i am designing the matching network of main amplifier as in my knoweldge i only can use one impedance to match to 50 ohm system impedance? If there is a method to use multi-impedance matching network please advice me.

 

[BigBoss]

Thank you. Which impedance have to use while i am designing the matching network of main amplifier as in my knoweldge i only can use one impedance to match to 50 ohm system impedance? If there is a method to use multi-impedance matching network please advice me.

In fact there are some difficulties while designing multimode matching circuit.As you know very well, first the main amplifier works and deliver to certain amount of power to the load then auxiliary amplifier involves just after efficiency starts to drop down.
So, the impedance won't be changed while this transition occurs except auxiliary amplifier changes the load ( or seen by main amplifier) by its output impedance ( of course coupling transmission line ).
All those stuff will impact the impedance which is seen by main amplifier and optimizing this and auxiliary amplifier is not easy.
There is no unique way to optimize such circuit, a good starting point is to use 7.311+j7.596 Ohm principal impedance then tweaking around this impedance may give you a concrete result.Other impedance is also not too far from this value.
I'm saying again that is not easy. Playing around impedance values will you bring somewhere not so bad.

 

[vivekroy]

What is more important to you? Back-off efficiency or peak power? If it's the back-off efficiency, design your matching network such that at backoff you see the optimum impedance. If its the peak efficiency, design your matching network for saturation. It's a trade-off which is why design of DPA is so tricky at very high frequencies.

Alternatively, you can use an optimizer to get a bunch of solutions and see which one fits your purpose.

I did come across a design procedure when I spent a lot of time on it. I never used it though. But feel free to give it a try: https://ieeexplore.ieee.org/document/7726022

 

[Mabrok]

@vivekroy & @BigBoss What are the most suitable technique that can be used to match these complex impedance to 50 ohm system impedance for 3.4-3.6 GHz band?

 

[Mabrok]

@vivekroy & @BigBoss What are the most suitable technique that can be used to match these complex impedance to 50 ohm system impedance for 3.4-3.6 GHz band?

How about quarter wave transformer impedance matching?