The Cyber-Spy.Com Usenet Archive Feeds Directly
From The Open And Publicly Available Newsgroup
This Group And Thousands Of Others Are Available
On Most IS NNTP News Servers On Port 119.
Cyber-Spy.Com Is NOT Responsible For Any Topic,
Opinions Or Content Posted To This Or Any Other
Newsgroup. This Web Archive Of The Newsgroup And
Posts Are For Informational Purposes Only.
Date: Wed, 13 Nov 2002 22:50:04 -0500
From: "Raymond E. Rogers"
X-Mailer: Mozilla 4.76 [en] (Win95; U)
Subject: Re: Niosy A/D converter - an advantage ?
X-Comments: This message was posted through Newsfeeds.com
X-Comments2: IMPORTANT: Newsfeeds.com does not condone, nor support, spam or any illegal or copyrighted postings.
X-Comments3: IMPORTANT: Under NO circumstances will postings containing illegal or copyrighted material through this service be tolerated!!
X-Report: Please report illegal or inappropriate use to
X-Abuse-Info: Please be sure to forward a copy of ALL headers, INCLUDING the body (DO NOT SEND ATTACHMENTS)
Organization: Newsfeeds.com http://www.newsfeeds.com 80,000+ UNCENSORED Newsgroups.
Roger Lascelles wrote:
> We have 12 bit ADC in a product. Due to grounding problems, the ADC
> readings fluctuate - I don't know exactly by how much, but lets say at least
> the last two bits dither around. The noise is digital hash from the
> microprocessor which has external RAM and ROM.
> Because the AD for is only used to measure periodic or DC quantities, the
> programmer has added a lot of averaging code which produces smooth readouts,
> to an equivalent of 13 bits resolution. He claims that the noise is an
> advantage, because it dithers the AD to permit averaging.
> Has anybody got experience of ADC dithering / noisy ADCs ? What are the
> dangers or limitiations with this sort of thing ? Are there gotchas with
> some types of noise ? Do you know of any articles or web links which would
> help ?
The IEEE had several articles in 80's that I know of. The long and
short is that dithering can increase the resolution and if the A/D trip
levels are stable the precision. You are still stuck with the A/D
accuracy specs though. You are basically trading off time for
precision. Perhaps the most extreme version might be considered to be
the delta sigma converters that have 100% full scale dithering that is
Dithering can smooth out the A/D steps for control purposes. This
reduces the impulses introduced by crossing the A/D steps. You can do
the calculations if you like but its probably better to just measure and
calculate the results. It does allow you push the control gain up a
little because you are sidestepping the A/D steps. This all gets a
little complicated though.
In theory you would like "unbiased" dithering. This can be done with
white noise or a ramp. The problem with letting the uP garbage do it is
that it might drift around as various different programs run. It would
be better to introduce it in a controlled way so you can calculate the
results. The easiest start is to imagine a four step ramp (synchronous)
and then walk through the calculations. This should show all of the
-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 80,000 Newsgroups - 16 Different Servers! =-----
Go Back To The Cyber-Spy.Com
Usenet Web Archive Index Of
The sci.electronics.design Newsgroup