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Use an opamp as a comparator or not?

Started by Piotr Wyderski December 21, 2017
On Fri, 22 Dec 2017 07:48:01 +0100, Piotr Wyderski
<peter.pan@neverland.mil> wrote:

>bill.sloman@ieee.org wrote: > >> It's a subject that comes up from time to time so a google search on "amplifiers as comparators" would have been worth the effort. >> >> http://www.analog.com/en/analog-dialogue/articles/amplifiers-as-comparators.html > >Yes, there is also a good TI analysis on the subject. The problem >is that there are two opposing camps, one says "never do that!" and >the other "actually, it's not that bad". The opamp will be fast >for other reasons, so I would like to know whether the 60x speed >margin is sufficient for reliable operation or not. > > Best regards, Piotr >
Some opamps, especially newer RRO types, make decent comparators in the 1 usec ballpark. Many/most older parts hang up on a rail and take forever to come off. The best thing to do is test candidates. I use LVDS line receivers a lot as RRIO comparators. They are not DC precise, but they are screaming fast, cheap, and have legal CMOS output levels. -- John Larkin Highland Technology, Inc lunatic fringe electronics