Any power stage could operate upto 6MHz? are there??

[banana]

The AD1994 is out now. If I'm reading the datasheet correctly, the switching frequency would be 6MHz

Are there any power stage design, that is capable of operating at such a high switching frequency?

Will IR2011 do? Or is it the time for discrete gate driver?

[classd4sure]

Hi,

You don't understand how this chip does what it does. Neither do I. However I can tell you it doesn't switch anywhere near that frequency. It would be silly to introduce a chip to the market that does, very few indeed would be able to make any use of it at all.

http://www.beis.de/Elektronik/DeltaS...eltaSigma.html

I find that link to be an excellent read!!!!!!!!!

Really, it should almost be a sticky here. (hint)

Anyway from what I've gathered of the data sheet which is extremely complete, switching frequency varies somewhere around 475khz.

Cheers

[Tekko]

Class D amplifiers are on the top edge 1-2MHz, but most are around 250-500KHz.

[Eva]

That's more 12V powered boom-box stuff rated at 10% THD and with pre-filter feedback.

They don't tell anything about it, but they are using special inductors (maybe shielded air cored) to obtain such low THD figures. In practice, when using mundane output inductors and capacitors, only the hysteresis from the cores will already account for more than 1% THD at medium powers (but they measure at 1W output).

Also, the 12.288 Mhz clock is for the delta-sigma modulator, not for the carrier. In practice, carrier frequency varies wildly and may be anywhere above 48Khz (modulator sampling frequency).

[phase_accurate]

I think they simply measured THD before the output filter.

It is quite interesting that a product by one of the most capable IC manufacturers is delayed by more than a year BTW.

Edit: Maybe this chip by itself could be used as modulator/driver for a more powerful amp.

Regards

Charles

[banana]

That was a great link! thanks

So 6MHz is only the sampling frequency. And the output spectrum might be implicit due to the delta sigma scheme........

Any suggestion on external power stage to boost more power?

[classd4sure]

Originally posted by phase_accurate
I think they simply measured THD before the output filter.

It is quite interesting that a product by one of the most capable IC manufacturers is delayed by more than a year BTW.

Edit: Maybe this chip by itself could be used as modulator/driver for a more powerful amp.

Regards

Charles

I've no doubt it could, very much like Zetex demonstrate in the data sheet for one of their modulators (I'm ignorant and won't check which).

Would it be worth doing though? I'd have to think performance would only get worse... I guess it depends alot on the drivers, both before and after.

Regards,
chris

[Lars Clausen]

I can also recommend a book on the same subject as the above link, it is the book where i got most of my inspiration for Class D amplifier construction.

It is IEEE no PC0274-1 Oversampling Sigma Delta Converters (Theory Design and Simulation) by James C Candy and Gabor C Temes.

It covers many of the same subjects as the link above, but maybe goes more indepth.

In practice, when using mundane output inductors and capacitors, only the hysteresis from the cores will already account for more than 1% THD at medium powers

Sorry i have to say, this claim from EVA is simply untrue. If so it would be impossible to make any kind of Class D amplifier with less than 0.3% THD. And we all know it is. Sorry EVA

[classd4sure]

Hi Lars,

Thanks for the book recommendation.

Regarding Eva's comment, keywords were "in practice", "mundane" and "medium powers", right along with the mention of them most likely using rather high end specialized inductors, just like you do to get good measurements.

It does make alot of sense that they'd go to great lengths in order to get optimal measurements for advertising, and such IC's often don't end up performing according to spec I understand.

It was also stated they don't measure at half power but at 1W, which further makes the measurements look better to the untrained eye, it really isn't telling of the true story (unless you know to look for all that they've omitted).

I think her comment was right on the money, and did a good job of demonstrating why it's just another junk box chip amp, destined for a 12$ radio.

Your quoted text took all that right out of context.

I find alot who don't begin to grasp class d yet and who are drawn in by the buzz going around often see these IC solutions as quick and cheap auto access to true high end audio. Personally I think that's a mistake, and it doesn't at all hurt to point out why it likely isn't as good as they try to make it seem.

That aside, Lars, what's your take on the IC solution, can ever be high end?

Regards,
Chris

[Genomerics]

Originally posted by Lars Clausen

Sorry i have to say, this claim from EVA is simply untrue. If so it would be impossible to make any kind of Class D amplifier with less than 0.3% THD. And we all know it is. Sorry EVA

Whilst I might disagree with EVA's 'statement' I still might pay attention for other reasons..... such as 'I wouldn't be so sure myself without looking closer'.

Of course you have done the sums before saying it is 'simply untrue'?

I think the point that was being made was that feedback was being taken prior to the output filter components.

I don't know much about this stuff myself other than the concept of a 1 bit oversampled A/D converter but I know as much as that a first order compensation (whoops it's a feedback loop) is naturally stable.

I would guess that references to second order loops really include a first order section at crossover.

What people care to do in the digital domain, after getting a digital answer, will be over my head.... and probably borrow terms from elsewhere, but it sounds like fiddling about.

Perhaps I should read more?

I think the basic point is this stuff needs pre-filter feedback because post filter feedback would make it go horribly wrong in a way that the digital johnnys would not have enough flexibility or the application engineers to deal with.

Fortunately, with pre-filter feedback they don't have to bother.

Problem solved!!(?????)


DNA