http://www.dspguide.com/ has the full text to the Scientist's And Engineer's
Guide to DSP. Chapter 4 (ADC And DAC) has a nice low-maths explanation of
how they work.

Wagner's quite right, except I believe that you will still find a few
high(ish) accuracy non sigma delta converters as sigma delta converters
aren't very appropriate for time domain encoded information (e.g. any form
of echo location system (sonar, radar et al)). Sigma delta converters (sigma
= sum, delta = change = sum of changes converter) produce a value that
represents the AVERAGE voltage in the conversion period (or average slope of
voltage (not commercially used I don't think)) rather than the instantaneous
voltage at a known point in the conversion process. i.e. in a 1kHz SD
converter you'd know the average coltage for each 1ms period. This is fine
for frequency encoded signals such as audio but if you need to know the
shape of a wave then they're not especially suitable.

Tom.
-----Original Message-----
From: Wagner Lipnharski [mailto:wagner@USTR.NET]
Sent: Thursday, April 13, 2000 2:11 AM
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: [OT] What is a Sigma-Delta AtoD converter? [EE]


All ADCs for high bit counting (bigger than 14 bits) use Sigma-Delta
conversion for a lower cost production. Sigma Delta use a capacitor ramp
measurement based on voltage comparison. They use integration, discharge
and other techniques to get great precision and accuracy. Actually they
are quire precise, and much cheaper than the regular instantaneous
multiple voltage comparison technique used in lower bit count.

<SNIP>

Wagner.

Mark Skeels wrote:
>
> Hi, folks.
>
<SNIP>
> I never heard of a Sigma-Delta AtoD converter before. Can anyone tell me
how
> it works, and has anyone had experience with this new part?
>
> Thanks on advance,
>
> Mark