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Load Pull transistor simulation

Azaro

Hello everyone,

I am trying to perform a load pull simulation of a transistor to verify some gain calculations I made using its S-parameters. Specifically, I have calculated the optimal conjugate impedances for the input and output to later calculate the power dissipated and transmitted in each stage of the transistor. Then, I only varied the output impedance and recalculated these powers, noticing that the power delivered to the load is lower.

Now, what I want to do is simulate this behavior using the Load Pull simulation. I have taken the model shown in the image, but I believe it is a linear model. My question is: if the chosen model is linear, is the load pull simulation accurate? In the calculations I made, nonlinearities are not considered. I don’t want to take nonlinearities into account.

In short, do you have any ideas on how to verify the calculations made with the transistor’s S-parameters through a load pull simulation?

Can you recommend any transistor model that is nonlinear and also has an S-parameter file?

Thank you very much in advance.

  • The S parameters are linear transfer functions and do not account for current or voltage, making it's impossible to determine power consumption. To accurately model the transistor and build an amplifier, a non-linear model is required.

  • in reply to OscPn

    Hello OscPn,

    Thank you for answering my inquiry. According to the books by Steve C. Cripps (RF Power Amplifiers for Wireless Communications) and Guillermo Gonzalez (Microwave Transistor Amplifiers), it is possible to determine power consumption in the design based on the theory of a linear RF amplifier. That is, without taking into account the nonlinear effects of the transistor.

    In these books, they explain how to calculate the amplifier gains (Gt, Gp, and Ga) through its S-parameters and by calculating the reflection coefficients. These gains are power ratios and are referenced to the source voltage (Vs).

    I understand that, in order to determine a more realistic physical behavior of the transistor, nonlinearities must be taken into account.

    But to verify those formulas, do you consider a load pull analysis accurate when using a linear component of the transistor? And what if I use a nonlinear one but make it operate in a linear region?

    Thank you very much for your attention.

  • in reply to Azaro

    While the text books (I have both of them) explain these determinations with a linear circuit, that will not work in a software tool.  What that means is that you must have a nonlinear model for the transistor.  Once you have a nonlinear model, you have 100% flexibility.  You can run this device with something like a satellite input (-100dBm) or you can push it well into compression with a high power input.  A nonlinear model can handle all of these extremes and everything between them.

    Load pull analysis is also 100% nonlinear.  There are several load pull examples in AWR - I suggest you do the following:

    On the main menu, select File=>Open Example

    When the example dialog opens, note that the keyboard is set to enter items in the text box at the bottom of the dialog.  Put this entry into the text dialog, and the number of examples will change from several hundreds to just a few: MWO Load Pull

    I recommend you take a look at 3 examples, and you should then be totally set up for load pull with AWR.  Start with  "Simulated_Load_Pull.emp".  Then take a look at both examples that deal with the main dealers that provide load pull items.  These two are "Focus_Load_Pull.emp" and "Maury_Load_Pull.emp"

    I hope this helps...

  • in reply to AWR Academic

    It has been incredibly helpful. I appreciate it a lot!

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