The non-linearity of power amplifier limits the power output efficiency. So, we can use DPD technique to improve it. But we need to know the power amplifier with the memory effect or memory-less. I hope that i can use some kind of test or experiment to verify it.
Memory effects also depend on driving level and signal condition. Therefore you need to define the conditions and specs such as modulation type, PAR, BO performance, etc. For example, if you use pulsed signal at the saturation region for the tests, recovery time of the transistor is very important for GaN HEMTs. It means, if you push another pulsed signal before recovering, you observe very high nonlinearity regarding the power level, bias pulse time, and pulse width. For me, the easyist way; If you have a DPD tool, you can try DPD functions with and without memory components. So you can have some idea about the memory effects of the amplifier regarding the signal type and power level. Another thing, you can check the AM/AM ad AM/PM situations. If you have very irregular trend, you can say your PA is very nonlinear at that region; and it can bring you more memory effects than regular behavior.
Dear Mr Osman Ceylan,
Thank you for your help.
I have another method to determine whether or not the PA has the memory effects. We can use "two tone test" to observe the 3rd, 5th and 7th intermodulation points. If the PA has memory effects, the right side powers of intermodulations are not equal to the left side powers of intermodulations. Otherwise, they are equal.
In my experiment, I found my PA has the memory effects in the 7th intermodulation. This is because the left side power of the 7th intermodulation is less than the right side of that.
However, I have another question. How can I observe the phase distortion (AM-PM)?
This question iv very interesting. To answer this question clearly one has to define exactly what is the memory effect in the power amplifier. There is a principle concerning the measurement of the quantities. The quantities are measured as they are defined.
Memory means to preserve information when the time elapses. So, it is a direct time domain effect. It is so that one can preserve a analog sample for specific time in a capacitor. So, if the devices are containing energy storage effect they will show some memory effect. The memory effect in an amplifier can be tested by applying a pulse on the amplifier and then observe how long this pulse can last after the input pulse is removed.
If there is no memory effect the two pulses will follow each other in the time variations. This is straight forward from the transfer characteristics of the strictly linear amplifier Vo= AVi with A is the gain, Vo is the output voltage and Vi is the input voltage. So Vo is a replica of the output and no memory effect at all.
So, we have to define the memory effect on time domain and then determine it in the frequency domain.
Best wishes
Dear Abdelhalim Zekry,
Thank you for your answer.
That is a good ideal to explain what memory effect is.
Best wishes
How can I simulate the memory effect of the power amplifier using Matlab?
You can measure the memory effect by applying a pulse on the input of the amplifier and follow the amplifier output with time. If the pulse lasts after the end of the input pulse with appreciable time, then it is said that the amplifier has a memory. If the amplitude of the rem-anent voltage is proportional to the input voltage then the memory is analog memory if it is constant with the amplitude of the pulse the memory will be one bit.
Best wishes
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