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March 15, 2011


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Mark Nelson

Hmmm. If you had done the bypassing with each rail's cap to ground (the way I was taught to always do it), you might never have experienced the problem, and you'd still have a high opinion of the company. The bypass cap connection from rail-to-rail doesn't seem like a good idea in general (though clearly specific conditions might make it necessary).

John Dunn

Hi, Mark.

Actually, I had tried it both ways and the op-amps did the same things. It was my choice to use the app-note's bypass plan to which the op-amp vendor decided to take exception, but the problem persisted either way.

Do check out that app-note though. It's quite edifying!

George Storm

Given the usual location of the "compensating" capacitor, I had expected the capacitor direct to ground would be between negative supply and ground (??).
Assuming "the other company" to have "merged" a couple of times since I first met them, I think I have used their products - and although they were sometimes more sensitive to layout there were other reasons to use them.
N.B. I love Paul Brokaw's humour.

John Dunn

Gotta take a look at that app-note again. It wasn't about a compensation capacitor of any sort, but about not unintendedly injecting rail voltage ripple into the current mirror circuits that in most op-amps are tied to the negative rail.

It's been too many years, so details elude me at this point, but that was the gist of the author's thesis.

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