Follow along with the video below to see how to install our site as a web app on your home screen.
Note: This feature may not be available in some browsers.
How to determine the impedance at combining node (Rcn) of doherty sub-amplifiers? Is it a standard for all DPA designs? Or depends on the design? Thanks in advancedView attachment 154540
This is the standard Doherty impedance that you see.
Rp=Rl' / (1 + I_carrier'/I_peaking)
Where I_carrier' is the current coming out of the quarter wavelength line in series with the carrier amplifier and I_aux is the current from the auxiliary amplifier. Rl' = Z_t^2/2R_L
This is the standard for current combining based Doherty PA. You can also have a voltage combining based Doherty which has different expressions.
Thank you. These equations can be used to design real DPA (to be fabricated)?
It serves as a starting point. It really depends on your frequency of operation.
A nice 'textbook' on the design of Doherty power amplifiers was published in 2018. https://www.oreilly.com/library/view/doherty-power-amplifiers/9780128098752/
Several different implementations exist, some examples of which are:
1. Using transformers: Look at the work by Ercan et al (Here is one of their papers from their research group: https://ieeexplore.ieee.org/document/7059254). This can also be done at lower frequencies and I think their first work was at 2.4GHz
2. Using transmission lines: Look at the paper by Hua Wang's group in ISSCC 2017. Personally, I found this approach to be much better at mmwave
3. Making Doherty combiners using a more mathematical approach: Look at the work done by Mustafa Ozen's group https://ieeexplore.ieee.org/document/8103016
In ISSCC 2019, they even proposed a digital Doherty which was a very nice publication.