Digital Delta-Sigma DAC

Hi all,

I want to design a digital delta-sigma DAC. It includes a pulse density
modulated module and RC low-pass filter.

The pulse density modulated module is a Delta-Sigma type (one adder and
one substractor). But why use Delta-Sigma type (i.e. how to understand
it)? Is there any good tutorial on digital Delta-Sigma?

Best regards,
Davy

"Davy" <zhushenli@gmail.com> writes:

> Hi all,
>
> I want to design a digital delta-sigma DAC. It includes a pulse density
> modulated module and RC low-pass filter.
>
> The pulse density modulated module is a Delta-Sigma type (one adder and
> one substractor). But why use Delta-Sigma type (i.e. how to understand
> it)? Is there any good tutorial on digital Delta-Sigma?

Wikopedia has some good information. At least yesterday it did.
-- 
%  Randy Yates                  % "How's life on earth? 
%% Fuquay-Varina, NC            %  ... What is it worth?" 
%%% 919-577-9882                % 'Mission (A World Record)', 
%%%% <yates@ieee.org>           % *A New World Record*, ELO
http://home.earthlink.net/~yatescr

Randy Yates wrote:
> "Davy" <zhushenli@gmail.com> writes:
> 
> 
>>Hi all,
>>
>>I want to design a digital delta-sigma DAC. It includes a pulse density
>>modulated module and RC low-pass filter.
>>
>>The pulse density modulated module is a Delta-Sigma type (one adder and
>>one substractor). But why use Delta-Sigma type (i.e. how to understand
>>it)? Is there any good tutorial on digital Delta-Sigma?
> 
> 
> Wikopedia has some good information. At least yesterday it did.

Hi Randy,

You mean "Wikipedia" - replace the 'o' with an 'i'.
http://wikipedia.org


-- 
Jim Thomas            Principal Applications Engineer  Bittware, Inc
jthomas@bittware.com  http://www.bittware.com    (603) 226-0404 x536
Being a good example is hard.  I'm trying to serve as a horrible
warning instead. - Brian Crane

Ayup. Of that's the way you spell ot.

:)

--RY

In sci.electronics.basics Davy <zhushenli@gmail.com> wrote:
: Hi all,

: I want to design a digital delta-sigma DAC. It includes a pulse density
: modulated module and RC low-pass filter.

: The pulse density modulated module is a Delta-Sigma type (one adder and
: one substractor). But why use Delta-Sigma type (i.e. how to understand
: it)? Is there any good tutorial on digital Delta-Sigma?

: Best regards,
: Davy

	Read, read, read!

	In any A/D or D/A circuit there is a quantizer -- the part of the 
circuit that actually does the conversion from analog to digital.  The 
error in quantization shows up as noise in the resulting signal.  The 
total power of this quantization noise only depends upon the number of 
levels in the quantizer, for any type of data converter (This is often 
stated as the distance between levels, which means pretty much the same 
thing.)

	In a nutshell, while most types of data converters result in 
quantization noise with a white spectrum (i.e. spread evenly throughout 
the signal band,) Delta-Sigma converters "shape" the noise, to move it out 
of the band of interest.  This is often combined with oversampling which 
has at least two advantages -- to spread the quantization noise out over a 
larger band (even without noise shaping,) and to be able to move the 
quantization noise far away from the band of interest, such that it can be 
subsequently filtered out relatively easily.

	Delta-Sigma modulation allowed for parctical A/D and D/A 
converters to be built that use as few as 2 levels (i.e. "1-bit 
converters") and have acceptable performance for data conversion of 
relatively low-bandwidth signals like audio (or slower) signals.  The 
reason why Delta-Sigma converters are usually used for low-bandwidth 
signals is because the oversampling ratio must be relatively high 
(around 100X) for good performance, which dictates how fast the system 
clock needs to run.

Joe
  

"Davy" <zhushenli@gmail.com> skrev i en meddelelse 
news:1137467765.105916.108520@g47g2000cwa.googlegroups.com...
> Hi all,
>
> I want to design a digital delta-sigma DAC. It includes a pulse density
> modulated module and RC low-pass filter.
>
> The pulse density modulated module is a Delta-Sigma type (one adder and
> one substractor). But why use Delta-Sigma type (i.e. how to understand
> it)? Is there any good tutorial on digital Delta-Sigma?

I would recommend books from the authors Richard Schreier, Gabor C. Temes, 
Steven R. Norsworthy and James C. Candy. Specifically the following books 
cover almost all subjects from end to other:

R. Schreier, G. Temes, "Understanding Delta-Sigma Data Converters", 2004
http://www.amazon.com/gp/product/0471465852/103-2515440-5710236
Very good introduction to the principles, with many examples. A more 
hands-on approach than many other books on the subject.

R. Schreier, G. Temes, S. Norsworthy "Delta Sigma Data Converters: Theory, 
Design and Simulation", 1996
http://www.amazon.com/gp/product/0780310454/103-2515440-5710236
Very detailed and in-depth coverage with good theoretical background on most 
subjects.

James C. Candy, Gabor C. Temes, "Oversampling Delta-Sigma Data Converters: 
Theory, Design and Simulation", 1991
http://www.amazon.com/gp/product/0879422858/103-2515440-5710236
A collection of important scientific papers that covers the full (almost) 
history of the development of this particular field of science. Very good 
supplement for the two other books.

I have read several other books on the subject, but none of them have the 
accuracy of these books. I would recommend not reading them cronologically, 
but start with the newest one, and then progress to the older books if you 
have a need for more background info or explanation of the theories.

-Thomas

Hi,

Thank you for your help!

I just want to learn the simplest one-bit Sigma Delta DAC.

And I found a link interesting:
http://www.embedded.com/shared/printableArticle.jhtml?articleID=22101730

I have one more question:
If I want the one-bit Sigma Delta DAC have better performance, shall I
accelerate the integrator (move the frequency Fs to higher frequency)?

Best regards,
Davy

Hi,

If you want to understand more about internals of ADC/DAC with
differentiation of various methods
I will refer one book

It titles something like Designing Methods of ADC/DAC from an author
named Joshpher...

I am very sorry that I am not able to give correct name of both book
and author but what ever I knew I have told I had referred this book
some time back.

But for delta sigma type of conversion you have to limit the data width
also as you increase the data width for more resolution the noise will
cause problems.

Thanks,
Regards,
Kedar

In sci.electronics.basics Davy <zhushenli@gmail.com> wrote:
: Hi,

: Thank you for your help!

: I just want to learn the simplest one-bit Sigma Delta DAC.

: And I found a link interesting:
: http://www.embedded.com/shared/printableArticle.jhtml?articleID=22101730

: I have one more question:
: If I want the one-bit Sigma Delta DAC have better performance, shall I
: accelerate the integrator (move the frequency Fs to higher frequency)?

: Best regards,
: Davy

	Yes, that is one way to achieve slightly higher performance.

Joe

"Davy" <zhushenli@gmail.com> writes:

> Hi,
>
> Thank you for your help!
>
> I just want to learn the simplest one-bit Sigma Delta DAC.
>
> And I found a link interesting:
> http://www.embedded.com/shared/printableArticle.jhtml?articleID=22101730
>
> I have one more question:
> If I want the one-bit Sigma Delta DAC have better performance, shall I
> accelerate the integrator (move the frequency Fs to higher frequency)?

You can read the presentation I made at the comp.dsp conference on
delta sigma conversion here:

  http://www.digitalsignallabs.com/presentation.pdf

See especially Figure 9 on page 18, which shows how SNR is related to
modulator order and oversampling ratio.
-- 
%  Randy Yates                  % "...the answer lies within your soul
%% Fuquay-Varina, NC            %       'cause no one knows which side
%%% 919-577-9882                %                   the coin will fall."
%%%% <yates@ieee.org>           %  'Big Wheels', *Out of the Blue*, ELO
http://home.earthlink.net/~yatescr