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Class D Amplifiers 101

Offler

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You mean this distortion? ;)
Precisely :). The argument went like that amplifier which does not use triangle wave will always be better, or because "D" stands for "digital" which I later found out to be wrong.

Even relatively cheap and simple UcD102 has THD+N at -80dB.
 

Kokoriantz

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I tried out my idea on post 62 to see the feasibility. I simulate it at standard 400khz and 50ns dt. This is without correction.
50ns 400khz.JPG

The distortion.
dis 400k 50ns.JPG

A roughly adjusted gives
400khz 50ns corrected.JPG

distortion.
dis 400k 50ns cor.JPG
 
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Kokoriantz

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What makes the amp better sounding at high switching frequencies is the very low ripple current. The kinks observed are separated by PP current of the ripple, running it at 2Mhz the the kinks will have shorter separation acting at very low power, very similar to under biased class AB. There the feedback acts as usual once at every zero crossing.
 

Kokoriantz

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Similar to class AB crossover distortion, though not exactly same. Odd and annoying in TPA32XX related circuits, when frequency gets higher and dead time is more pronounced.
It looks like the dt correction is voltage sense as it is optimized for 3ohms load.
3 ohms tpa3255.JPG
4ohms tpa3255.JPG
8ohms tpa3255.JPG
 

Kokoriantz

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Here is 10ns dt and 2Mhz Fs. The pair kinks got merged to make a smooth zero transition, only each polarity now is lacking an offset as the distortion is about 0.5%. The feedback can operate now much better in the lack of abrupt kinks, as the frequency is high 60db NFB can be easily applied to bring the number 0.0005%.
dis10ns 2M.JPG
10n 2M.JPG
 

JohnYang1997

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