D
Deleted member 27948
Guest
Dear Audio Scientists,
Recently I had fun simulating crossover distortions in Class-AB amplifiers with nested feedback loops.
It was quite interesting and I would like to share the results of my study:
1) It's a bit more productive to look at feedback as means to take a derivative of distortions rather than a plain attenuator of distortions.
2) Being a differentiator, feedback "shifts" non-linear distortions to high frequencies
3) Feedback can be nested, with each loop shifting the distortions up and up.
4) By itself, no amount of fedback can eliminate distortions, but their high-frequency remnants can be filtered with a passive LC filter, same as in class-D.
5) The end distortions are inversely proportional to Iq and Gain Bandwidth Product of amplifier, for nested feedback GBP^n
An example of such design loosely based on "blameless" amplifier by D. Self, with two 2nd-order feedback loops:
Here are the distortions of the "blameless" amplifier itself, for Iq=20mA, 20kHz 100W. Only the envelope of harmonics is plotted in frequency domain, not the mess between harmonics because that mess is due to calculation errors and has nothing to do with reality.
and here are the distortions for the entire design:
A full description of the MATLAB package with LTspice schematics can be found at: https://www.mathworks.com/matlabcen...crossover-distortions-in-class-ab-0-00002-thd
As with any simulations untested in the real-life, you can never be 100% sure that it's all true but... please let me know how and where I screwed up.
Recently I had fun simulating crossover distortions in Class-AB amplifiers with nested feedback loops.
It was quite interesting and I would like to share the results of my study:
1) It's a bit more productive to look at feedback as means to take a derivative of distortions rather than a plain attenuator of distortions.
2) Being a differentiator, feedback "shifts" non-linear distortions to high frequencies
3) Feedback can be nested, with each loop shifting the distortions up and up.
4) By itself, no amount of fedback can eliminate distortions, but their high-frequency remnants can be filtered with a passive LC filter, same as in class-D.
5) The end distortions are inversely proportional to Iq and Gain Bandwidth Product of amplifier, for nested feedback GBP^n
An example of such design loosely based on "blameless" amplifier by D. Self, with two 2nd-order feedback loops:
Here are the distortions of the "blameless" amplifier itself, for Iq=20mA, 20kHz 100W. Only the envelope of harmonics is plotted in frequency domain, not the mess between harmonics because that mess is due to calculation errors and has nothing to do with reality.
and here are the distortions for the entire design:
A full description of the MATLAB package with LTspice schematics can be found at: https://www.mathworks.com/matlabcen...crossover-distortions-in-class-ab-0-00002-thd
As with any simulations untested in the real-life, you can never be 100% sure that it's all true but... please let me know how and where I screwed up.