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From: Jeroen Belleman <jeroen@nospam.please>
Newsgroups: sci.electronics.design
Subject: Re: Is anybody using NE521 comparators?
Date: Thu, 26 Sep 2024 15:07:50 +0200
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On 9/26/24 13:04, Jean-Pierre Coulon wrote:
> "offset" has a particular meaning for its designers. Tha datasheet says: 
> output undefined if abs(Va_Vb) < offset. Forget what you know about the 
> offset of an opamp! One could expect better from a bipolar differential 
> pair :-)

It's Va-Vb, the difference. Not Va_Vb.

They mean that they can't tell if the output will be either
high or low; Not that it is hovering somewhere in between.
This is pretty much what one should expect from a comparator
offset. Of course, for *really* small inputs, the output
will start wiggling randomly. You're not supposed to go there.

I agree Vos=6mV is pretty poor for a bipolar differential
comparator, but hey, this is an old design. It can easily
compare voltages less than the offset, but you'd have to
get serious about correcting for it. It gets slower, too.

Jeroen Belleman