Rotating memory data recovery

From: Paul Koning <pkoning_at_equallogic.com>
Date: Tue Sep 14 08:21:35 2004

>>>>> "Gordon" == Gordon JC Pearce <gordon_at_gjcp.net> writes:

 Gordon> Obviously, the higher the resolution, the slower the
 Gordon> conversion. Most A-D converters (and I'm sure many, if not
 Gordon> most of you know this) use "successive approximation" to
 Gordon> derive the correct value - get a D-A converter and a
 Gordon> comparator, then loop through "toggle the MSB, is it too high
 Gordon> or too low? Toggle the next bit, too high or too low?" all
 Gordon> the way down. You get "flash" converters for video (or you
 Gordon> used to) which were 32 or 64 individual comparators and
 Gordon> voltage references, and some encoding logic to give you a
 Gordon> binary output. Overkill really, but very, very fast. If you
 Gordon> found a fast 6-bit flash converter cheaply, that may well be
 Gordon> enough resolution for your track scanner. We're not going
 Gordon> for Dolby Digital quality here...

Flash converters certainly go up to 8 bits, perhaps more by now.

Also, modern SAR converters are often hybrids -- flash for the high
order bits, SAR tweak for the low order bits.

Then there are sigma-delta converters, particularly well suited for
very high resolution at relatively modest speeds.

"Relatively modest" is subject to change. I just saw an Analog
Devices ad describing their new 2 megasample per second 18 bit SAR
converter, and a 20 bit S-D converter at 2.5 megasamples. I don't
suppose those are "relatively cheap" though...

        paul
Received on Tue Sep 14 2004 - 08:21:35 BST