Rotating memory data recovery

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