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Design >> Mixed-Signal Design >> sigma-delta DAC for audio
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Message started by Dan Clement on Feb 9^th, 2010, 8:34pm

Title: sigma-delta DAC for audio
Post by Dan Clement on Feb 9^th, 2010, 8:34pm

Forum:

Please point me to a PRACTICAL reference on how to design a sigma-delta DAC for audio applications.

I need some examples of real hardware, not just more math as is found in all the classical references.

I also need guidance on dithering.

Thanks in advance!

-Dan

Title: Re: sigma-delta DAC for audio
Post by loose-electron on Feb 10^th, 2010, 3:13pm

Chapter 7
"Understanding Delta Sigma Data Converters"

By Schreir & Temes

IEEE press, , Wiley Interscience
ISBN 978-0-471-46585-0

Probably the best thing out there and even it is a pile of analaytical math as well.

Cant offer anything better and I think I have everything that's been published on the topic.

Title: Re: sigma-delta DAC for audio
Post by Dan Clement on Feb 10^th, 2010, 8:40pm

Thanks.

I have quickly found that nobody seems to have any examples of a real implementation, especially for a second order and above.

I wonder why that is...

Does this mean I shouldn't use this kind of design? :)

-Dan

Title: Re: sigma-delta DAC for audio
Post by yvkrishna on Feb 10^th, 2010, 11:14pm

Hi Dan Clement,

No doubt sigma delta DACs are the best choice for audio applications with high snr requirements.

this reference talks about a survey of interpolation filters used in sigma delta dacs for audio .

http://www.scribd.com/doc/20203269/Interpolation-filters-for-oversampled-audio-DACs

Regarding the modulator please refer to sigma delta toolbox which is exhaustive

http://www.mathworks.com/matlabcentral/fileexchange/19

some other useful refs are
An FPGA-based Re-configurable 24-bit 96kHz Sigma-Delta Audio DAC

Higher order implementations have stability issues, that may be the reason for you to not find enough references.

Regards,
yvkrishna

Title: Re: sigma-delta DAC for audio
Post by vivkr on Feb 11^th, 2010, 2:32am

Dan Clement wrote on Feb 10^th, 2010, 8:40pm:

Hi Dan,

There are plenty of good implementations although it is unclear what exactly you want to see. It would be very difficult to find a paper discussing basics like choosing NTFs etc. That part is identical to choosing an NTF for an ADC but with the difference that you almost always use error feedback structures in a DAC (only realistic for delta-sigma DACs anyway).

That being said, the yellow book by Norsworthy, Schreier and Temes has some practical design examples in one chapter, one of which covers a DAC (by Sooch et. al. I think). The green book by Schreier and Temes also has example designs. Then there is the classic paper by Testsuro Sugimoto. Just go to the SSCS website and look for the best papers from the JSSC.

Regards,

Vivek

Title: Re: sigma-delta DAC for audio
Post by Berti on Feb 11^th, 2010, 3:31am

Hi Dan Clement,

Vivek is completely right: There are many good paper about implemented ΔΣ ADCs.
Just use ieeexplore (if you have access).

Cheers

Title: Re: sigma-delta DAC for audio
Post by Dan Clement on Feb 11^th, 2010, 7:35pm

Thanks all.

Vivek, what I am really struggling to find is a practical example of a real life, RTL example, or even a block diagram implementation of a second order DAC.

The books are all about the math and yes that's important, but I have a hard time drawing a line between the high level theory and how to build it with RTL and logic gates.

I will check out all the references I've been provided and I will come back with specific questions if I can't get there.

thanks!
-Dan

P.S. to clarify i'm looking for help with a DAC not an ADC...

Title: Re: sigma-delta DAC for audio
Post by vivkr on Feb 12^th, 2010, 1:44am

Dan Clement wrote on Feb 11^th, 2010, 7:35pm:

Dan,

I was also referring to DACs (note my mention of error-feedback structures). There are papers by Fujimori in the Dec. '98 (low-power, cheap audio DAC), and Aug. 2000 (high-performance audio DAC) in the JSSC. The reason for mentioning ADCs was simply that the math applies equally well to ADCs as well as DACs.

That being said, the thing you are looking for is not easy to find anywhere. You would need to search for courses (maybe on some univ websites) or look for professional courses on delta-sigma DAC design or digital filter design. I cannot imagine that the techniques used are any different from that in most conventional digital design, particularly filter design. However, I have never had to make a delta-sigma DAC myself.

Finally, the yellow book (Schreier, Norsworthy, Temes) covers DACs in Chapters 10 and 12, and the green book by Schreier and Temes covers DACs in Chapters 7 and 9, with practical examples. Even Johns & Martin has some basic stuff about the subject.

Regards,

Vivek

Title: Re: sigma-delta DAC for audio
Post by Dan Clement on Feb 12^th, 2010, 4:49am

Thanks!