> 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))
>
        I think that this is a dual slope style converter that your are
thinking of
        Sigma is to integrate. This is done in the front end
        of the converter so that the rate of change in the incomming signal
is reduced, so then the delta area can run
        at a lower speed so as to produce a small rate of change in period,
it is then the period of the rate of change of the output multiplied by the
sigma value that then represents the actual input value.

        A simple signal delta converter of this type can be represented as
the following:-

        input-------> sigma--------------Comparator----------->output

        (forgive the ASCII art)


> 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.
>
        OK you are talking about averaging here so I do think that the
converter you are looking at is a dual slope type, and is good for removing
CMR.

>  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
        Only for slope converters, else my current DSP project would not be
working :), else we  would also have to come up with a valid explanation as
to why Sigma Delata converters are used in the French radar system and in
the Australian Jindalee over  the horizon radar


        Dennis





> 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