Delta Sigma converter

lawlopez

Teh SX28 has a comparator, the first 4 io pins can do rail to rail,
doesn't this mean you could make a delta sigma a/d converter ?
Not that I really know what that is, I'm still working it out.

Just curious.

I was wondering if anyone did this and what problems they
ran into.

No, don't send me any code that would be the fun part to do.

Thank you,
larry

pjv

Hey Larry;

You bet!

There are (or at least were) some app. notes on the Ubicom site for exactly that. An A/D converter can be made with less than a dozen lines of code, two resistors an one small capacitor. The simplest is 8 bits of resolution, but you can make shorter and longer ones as well.

For fun I made one that was 4 bits, and hence it was 16 times as fast as the 8 bit, and I was also able to get 12 bits running quite reliably, at 1/16 the speed of the 8 bit version.

In all those cases I did not use the comparator, but let the CMOS input switch level (half of rail) do that work, so that makes things very easy.

I messed with a 14 bit, but the SX's switching noise gets in the way, even with using the comparator. I suspect it can be done, but that was just for fun, so I did not pursue it too far.

Makes a great little A/D; I can't figure why everyone is interfacing external A/D's to the SX while the simple embedded internal solution is staring them right in the face, with less code than it takes to interface an external chip.

Two resistors, one small cap, 10 instructions, delivers up 8 bits..........go figure!

Cheers,

Peter (pjv)

lawlopez

Thanks Peter.
I found it.
Very nice app notes, too.
Perhaps I'll understand them now!!!
Larry

Post Edited (lawlopez) : 11/7/2005 2:35:34 PM GMT