Favourite low offset op-amp

It actually works *better* with a crude transistor amplifier.

Best regards, Spehro Pefhany

AD8551, prob. overkill for your application, 1uV offset, sold as a zero drift op amp. Just used these as a thermopile amplifier, they are simply amazing. At $2.30 in singles from Digi Key they are a wonder!

Rocky

Hello Graham,

If you can afford to do auto-zero as Bill suggested and your opamp budget really is 15 cents for a dual: Why not use ye olde LM324 and clamp to zero? Ok, you'd have to spring another 5c or so for a BSS123 to do the clamping but a quad LM324 can be had for around 10c.

Regards, Joerg

Hello Winfield,

Yes. I wish they were teaching this kind of thinking at universities (at least at mine they didn't). There is almost always a chance to do even the most challenging designs with jelly bean components. Even though I prefer M&Ms over jelly beans.

Regards, Joerg

Hello Jim,

Yes, although he was suggesting the use of an LTC auto-zero amp which are expensive.

Me, too. But I like the old fashioned word "clamping" better. Even the vintage tube TV sets did that already to set the proper black level.

Way to go. It'll even work with a crude transistor amp.

Regards, Joerg

Hello Jim,

Or maybe he is too young. In my days choppers were those motorcycles with extremely long handle bars, where the front wheel was way out there and you wore a bandana and some cool tattoos. Oh, and it had to be loud.

Regards, Joerg

Tis now

martin

After the first death, there is no other. (Dylan Thomas)

The AD8551 has an absolute maximum supply voltage of 6V, which doesn't fit too well with Pooh Bear's +/-17V rails.

That's why I suggested the LTC1150 - which can take +/-16V rails.

It's always a good idea to read the whole posting before responding - I didn't notice the +/-17V on the first pass either, and had to rewrite my response in consequence.

-------------- Bill Sloman, Nijmegen

We introduce the auto-zero circuit as well, pg 392.

But I was doing it before you were born ;-)

Actually, IIRC, I ran across those notes here at the house, so they're not buried in the archival storage. I'll post if I can re-find.

...Jim Thompson

It's one of those devices that started out as a typical high performance "$5 op-amp" and has happily slid into jellybeanitude (genericity?) over the years, with several reliable suppliers currently online.

Some of National's 1A/3A Simple Switcher line seem to be going the same way, over time, VERY slowly.

Best regards, Spehro Pefhany

See...

Newsgroups: alt.binaries.schematics.electronic Subject: uV Meter with Auto Zero - AutoZeroNotes.pdf Message-ID:

Early '70's

...Jim Thompson

The application is to 'dc servo' part of an amplifer stage that by design isn't capable of high DC precision. Basically need to counter some Vbe mismatches.

Graham

Certainly best bet so far. I'd forgotten it. I'm sure I used one about 20 yrs ago as a photodiode amplifier.

Graham

Astonishingly low offset.

Hmmm only 5V single rail though.

Graham

Hi Joerg,

is this like the 'chopper' concept ? I'm not familiar with this - other than conceptually.

Hmmm - I ought to add that I need my input to be differential !

Graham

LOL ! I would say 'snort' but that might come over wrong !

Graham

My first precision autozero amplifier design was in 1965.

Before that they were what my grandmother put in the glass of water by the side of the bed at night.