From: John Larkin
Subject: Re: Niosy A/D converter - an advantage ?
Date: Wed, 13 Nov 2002 20:14:32 -0800
Organization: Posted via Supernews, http://www.supernews.com
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On Thu, 14 Nov 2002 14:28:03 +1100, "Roger Lascelles"
>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
Noise+averaging will extend resolution nicely. It's used in
temperature controllers, electronic electric meters, and
communications applications. I make a thermocouple temperature
controller with a 12 bit ADC that gives about 16 bits effective
resolution; the front-end opamp alone makes all the noise we need.
Just make sure the noise is uncorrelated to the sample rate; that may
be a problem using noise from the uP bus. It's also best if it has a
smooth probability distribution; gaussian and flat PDs both work well.