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Class D Switching Power Amplifiers and Power D/A conversion

Class D investigation.
Class D investigation.
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Old 4th January 2017, 12:58 PM   #1
kees52 is offline kees52  Netherlands
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Default Class D investigation.

Hi All


First I wish the people here a happy and audiophile 2017.

I did post some on thread's but better is my own one.


I have a thread here also with a allfet circlotron however I wait for parts and so I have to do something els to eat my time on the end of the lazy year.

I thought I do test some digital amps, or better class D switching amps, as I did read everywhere the HD of them but also the kind of sound quality is wide spread as from hars to warm, and even a single ended tube warm sound.

The technology behind this amps is very wide, sigma delta where some 001 is fill in with 011 fo get lower switching and self oscillating UCD, the last I did some reading on, with multipole HD shaping we can get very low HD.

see some excamples, I have sims discrete power comparator in picture 3 and 4 the first are just a complemmentairy stage after a comparator chip, the chips used are very fast..

To get good sound the choose of opamp is important, that is why I use burr brown opa 2365 or single one opa365 who is allfet but nog yet do I now how it sounds, this is later care..

regards
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Old 4th January 2017, 08:18 PM   #2
Pafi is offline Pafi  Hungary
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Faster distortion simulation:
- Simulate only 2 periods! (I usually use 1 kHz, 2 ms.)
- Set "Time to start saving data" to the start of 2nd period (1 ms)!
- FFT can "Use Extent of Simulation Data".
- Don't use any windowing function!

Above is for fast but still accurate analysys. But if there is some weird aperiodical (transient) behaviour, or signal freq is not exactly known, then you may have to use multiple periods (even if not exactly whole periods) and to smooth the fractional period by windowing. For exact amplitude reading flat-top windowing is the best, but it may hide some fine details. Generally Blackmann-harris is good. But use windowing only if many periods of the interesting freq is available for analysis!
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Last edited by Pafi; 4th January 2017 at 08:46 PM.
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Old 4th January 2017, 08:50 PM   #3
Pafi is offline Pafi  Hungary
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HF portion of the plot is useful for checking Sw freq variation, but using too much data makes it harder to see.
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Old 4th January 2017, 09:11 PM   #4
TNT is offline TNT  Sweden
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Do you have some insight in why almost all Class D amps has a distorsion peak at around 4-5k and then to drop to lower values again at say 10khz?

//
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Old 4th January 2017, 09:38 PM   #5
kees52 is offline kees52  Netherlands
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Hi Pafi


Thanks for the info, I have did some tests to see what happens, see the pictures.

TNT you did ask Pafi? because I did not see these peaks on sim, but did use a HD shaper as was on papers, did try some different things to learn and see, class D is not such playtool als liniair amps, she are quite complicated, also in pcb design.

See on plot that the carrier is on 1.5 Mhz, but when I come close to rails it drops to 700 khz. this is to high and bad for EMI.

regards
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Old 4th January 2017, 10:03 PM   #6
doctormord is offline doctormord  Germany
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Quote:
Originally Posted by TNT View Post
Do you have some insight in why almost all Class D amps has a distorsion peak at around 4-5k and then to drop to lower values again at say 10khz?

//
Switching over filters in the AP.
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Old 4th January 2017, 10:34 PM   #7
kees52 is offline kees52  Netherlands
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I did sim with your setup Pafi

see the result, is this what you mention.

regards
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Old 4th January 2017, 11:01 PM   #8
Pafi is offline Pafi  Hungary
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Quote:
Originally Posted by TNT View Post
Do you have some insight in why almost all Class D amps has a distorsion peak at around 4-5k and then to drop to lower values again at say 10khz?

//
It drops because measured through a very sharp 20 kHz low pass filter what filters out 3rd harmonic as soon as signal freq exceeds 6.6 kHz. (Or simply FFT components above 20 kHz are ignored.) The increasing part is due to decreasing loop gain. Measured the same way all amps behave this way, not only ClassD, but this strict bandwidth limit is not always applied to linear amps.
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Old 4th January 2017, 11:19 PM   #9
TNT is offline TNT  Sweden
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Aha - thanks!

//
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Old 4th January 2017, 11:35 PM   #10
Pafi is offline Pafi  Hungary
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Quote:
Originally Posted by kees52 View Post
Hi Pafi

Thanks for the info, I have did some tests to see what happens, see the pictures.

See on plot that the carrier is on 1.5 Mhz, but when I come close to rails it drops to 700 khz. this is to high and bad for EMI.

regards
I don't know what you changed and what do you expect.
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