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From: Joerg on 12 Sep 2006 16:43 Hello Jim, >>> >>> We generally don't anymore. We tried a design using an AVR's internal >>> comparator. The next revision put it back in an external device. On the >>> other hand the ADC has been adequate for a lot of purposes. Our general >>> policy now is that any internal analog components on uCs should be >>> presumed worthless until proven otherwise, especially considering the >>> lack of adequate specifications. We suspect they let the digital guys >>> build them for fun or something. :) >> >> Sometimes it looks like it. It is also a reason why I never used SoC. >> Even a puny 10c opamp can often run circles around what's in there. >> Whenever I looked at the "analog" offerings in uC or SoC devices I >> couldn't resist the urge to yawn. Then did the whole design analog, >> like usual. Ended up being lower in cost anyways. > > Yes, it certainly pays to look for Analog performance from the companies > that cut their teeth on analog, and added a uC, and not vice-versa. > > So, TI, Analog Devices, and SiLabs offer 24 bit ADCs and well spec'd > 12 bit ADCs, and their Comparators are Rail-Rail, on their uC. > > I know an AVR user whose ADC performance measurably degraded on a > generation upgrade [90S -> mega]. > > Tip: if you NEED ADC performance, and the spec sheet has empty MAX > columns, or no supply range or Temp range included, just pause and > think "why do they leave off that info ?" > Or when you have bugged them 3-4 times about some more detailed ADC specs and they promised to get back to you but never do, just pause and think "Why don't they have an answer here?" :-) Oh heck, maybe I'll have to do the next one totally analog as well. The downside is that I'll have to push a few filters and their CF has to be programmable. Not that I haven't done that analog before but that is no fun. -- Regards, Joerg http://www.analogconsultants.com
From: steve on 12 Sep 2006 16:49 Jim Granville wrote: > I know an AVR user whose ADC performance measurably degraded on a > generation upgrade [90S -> mega]. > > Tip: if you NEED ADC performance, and the spec sheet has empty MAX > columns, or no supply range or Temp range included, just pause and > think "why do they leave off that info ?" > At first I thought it was because it was known but wasn't very good, but from your generation upgrade example above, maybe it isn't known. Maybe the lack of max spec allows them to move to a different process or package (maybe in different plants around the world) without spec updates? Some plants/ may produce very good A/D's, while others, for whatever reason, cannot, and they simply don't know ahead of time which plant will make which chip in which package, just a guess.
From: Joerg on 12 Sep 2006 16:54 Hello Steve, > >>Some of them actually do. They check out the performance themselves. > > I wouldn't think that is possible by using one or several samples, > don't you have to know about the chip manufacturing process variations > to characterize the performance of a part made 6 months from now? > > Individual parts sometimes perform way better (and I mean like an order > of magnitude better) then the max worse case specifications. > Well, yes, that's why I never do that for production runs. Never did. The sole exception may be once in a blue moon projects or specialty apps such as when you have to avalanche an RF transistor. There you can hardly get away without screening. -- Regards, Joerg http://www.analogconsultants.com
From: Joerg on 12 Sep 2006 16:57 Hello Steve, > >>Sometimes it helps to communicate before a chip design and not after. >>Example: IMHO the decision by TI to take the ADC function out of the new >>HW-multiplier equipped F2xxx device was not a good decision. It'll cost >>design-wins. > > I'm not aware of these new HW multiplier F2 parts, is there a link > somewhere with the announcement? > I heard it from someone I know at TI. No idea if there was a formal announcement but it's this one: http://focus.ti.com/docs/prod/folders/print/msp430f2350.html MSP430F2350 in case the link doesn't work for you. -- Regards, Joerg http://www.analogconsultants.com
From: Joerg on 12 Sep 2006 17:01
Hello Steve, > >>I know an AVR user whose ADC performance measurably degraded on a >>generation upgrade [90S -> mega]. >> >>Tip: if you NEED ADC performance, and the spec sheet has empty MAX >>columns, or no supply range or Temp range included, just pause and >>think "why do they leave off that info ?" >> > > At first I thought it was because it was known but wasn't very good, > but from your generation upgrade example above, maybe it isn't known. > > Maybe the lack of max spec allows them to move to a different process > or package (maybe in different plants around the world) without spec > updates? Some plants/ may produce very good A/D's, while others, for > whatever reason, cannot, and they simply don't know ahead of time which > plant will make which chip in which package, just a guess. > I remember an unspoken instruction at a fab: Don't start process xyz on a cold winter day unless it rains or snows. I believe it had something to do with ESD. Lots of "seat-of-the-pants" flying but I don't know if it's still so prevalent these days. -- Regards, Joerg http://www.analogconsultants.com |