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Power amplifiers

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7 months 2 weeks ago #819 by dave.aarsh
dave.aarsh created the topic: Power amplifiers
Hello all,
I am starting to design a power amplifier. I have read some articles about the stability of the power amplifiers. Can anyone suggest what should I look other than K factor to see the stability of my power amplifier. I want to be certain that my amplifier will not oscillate at any random frequency.

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7 months 6 days ago #820 by Desert Sage
Desert Sage replied the topic: Power amplifiers
You haven't told us the operating frequency or the number a gain stages. Both of which would be helpful information.

It is very important to keep the signal off of the dc supplies to prevent oscillations. Also, the cavity width the active devices are in should provide enough isolation from output to input to provide sufficient gain margin to prevent oscillation. This can be estimated using waveguide below cutoff calculations. I think that info can be found on this site.

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6 months 1 week ago #829 by Microwaves101
Microwaves101 replied the topic: Power amplifiers
Keep the gate voltage away from the drain voltage if you are using FETs, at least until you are on th eother side of a regulator. Capacitive feedback can cause oscillations.

If you are power combining devices reactively there are special considerations which we have never dealt with on this site. One example paper is by Platzer and Struble, there are certainly other references on this. I think I will try to chase down Wayne Struble to make a M101 page on this topic soon.

ieeexplore.ieee.org/document/512515/

Steve

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6 months 1 week ago #834 by MMWENGR
MMWENGR replied the topic: Power amplifiers
Balanced amplifiers can exhibit what is referred to as odd mode instability that is not predicted by the standard K and B stability factors. Ronald Freitag has published papers on this topic.

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6 months 1 week ago #835 by rob
rob replied the topic: Power amplifiers
K-factor will only give an indication of even-mode stability. Odd-mode instability is not just an issue for balanced amplifiers, it needs to be considered whenever power from multiple devices is combined. What kind of power amplifier are you trying to design?

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6 months 6 days ago #836 by Microwaves101
Microwaves101 replied the topic: Power amplifiers
Check out our new page on normalized determinate function (NDF). If it does not already, it will soon have some download presentations on the topic.

It is a lot to wrap your head around, but highly recommended to use this technique in power amplifier design.

Steve

microwaves101.com/encyclopedias/normaliz...rminate-function-ndf

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