Favourite low offset op-amp

Rich Grise · May 17, 2005

On Tue, 17 May 2005 14:28:23 -0700, Jim Thompson wrote:

On Tue, 17 May 2005 21:11:20 GMT, Joerg
notthisjoergsch@removethispacbell.net> wrote:

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

http://www.analogconsultants.com

Bill? Did I miss an actual technical contribution by Sloman ?

Jim, are you mellowing out in your old age? ;-)

I love auto-zeroing.

Once upon a time, I even built a micro-voltmeter, using LM324's, to
measure voltage drop on PCB tracks, to locate shorts.

Zero, measure, zero, measure....

You built stuff? I thought all you did was ideate and simulate. ;-)
Oh, right - at our age, we don't have time for all that trimming and
crap, right? ;-)

Cheers!
Rich

John Larkin · May 17, 2005

On Tue, 17 May 2005 16:18:53 -0700, Jim Thompson
<thegreatone@example.com> wrote:

On Tue, 17 May 2005 16:05:53 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 17 May 2005 15:43:53 -0700, Jim Thompson
thegreatone@example.com> wrote:

On Tue, 17 May 2005 15:12:11 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 17 May 2005 21:48:26 GMT, Joerg
notthisjoergsch@removethispacbell.net> wrote:

Hello Jim,

Bill? Did I miss an actual technical contribution by Sloman ?

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

I love auto-zeroing.

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.

Once upon a time, I even built a micro-voltmeter, using LM324's, to
measure voltage drop on PCB tracks, to locate shorts.

Zero, measure, zero, measure....

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

Double-emitter choppers.

John

You're showing your age, John. And they weren't all that wonderful...
CMOS is MUCH better.

...Jim Thompson

Varicap parametric bridges.

John

What did they call the big-ass ones.

I vaguely remember using some kind of varactor to triple me up to the
2 meter band. (5W

...Jim Thompson

Burr-Brown did a very impressive potted-brick opamp using modulated
varicaps in the front end; CMRR was about infinite, as the entire
input circuit was transformer-coupled. I think Bob Pease did an
article on it. I seem to recall that TI did a monolithic varicap opamp
at some point... I may have a datasheet in The Dungeon.

Paramps are cool. Somebody did a paper on using ceramics caps as
active gain elements, and I have a paper on making nonlinear
transmission lines (shock lines) using the nonlinearity of ceramic
caps.

Just because I know about this stuff doesn't mean I'm old enough to
have experienced it all first-hand.

John

Joerg · May 17, 2005

Hello Jim,

Double-emitter choppers.

You're showing your age, John. And they weren't all that wonderful...
CMOS is MUCH better.

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

http://www.analogconsultants.com

Jim Thompson · May 17, 2005

On Tue, 17 May 2005 16:52:36 -0700, John Larkin
<jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

[snip]

Paramps are cool. Somebody did a paper on using ceramics caps as
active gain elements, and I have a paper on making nonlinear
transmission lines (shock lines) using the nonlinearity of ceramic
caps.

Just because I know about this stuff doesn't mean I'm old enough to
have experienced it all first-hand.

John

480)460-2350 | |
| E-mail Address at Website Fax

Jim Thompson · May 17, 2005

On Tue, 17 May 2005 23:54:43 GMT, Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Hello Jim,

Double-emitter choppers.

You're showing your age, John. And they weren't all that wonderful...
CMOS is MUCH better.

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

http://www.analogconsultants.com

Reminds me when we first met the daughter-in-law's family.

My son, bride-to-be and her mother show up in the bride's Honda Civic.

They say that father is on the way.

All of a sudden the house is shaking, and this crazy, hippy-looking
guy, with a bandanna, comes up the hill on a Harley chopper... so loud
that all the neighbors pour out of their houses.

It's the father-of-the-bride. Turns out he's a big-time dealer in
Harley parts in LA (now moved to Palm Springs).

Then he took off the bandanna... it had a velcro closure. I gave him
a ration of shit for lack of authenticity ;-)

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice

480)460-2350 | |
| E-mail Address at Website Fax

Pooh Bear · May 18, 2005

Winfield Hill wrote:

Pooh Bear wrote...

Winfield Hill wrote:

Pooh Bear (Graham) wrote...
Bernhard Kramer wrote:
Pooh Bear a écrit:

I have an application where I'm looking for a low input voltage
offset op-amp. I'd like 100uV or so typical and don't want to
pay much. Lowish input current is desirable too.

Speed isn't an issue, nor is very low noise or single supply
operation. In fact I *want* to run it off +/- 17V.

One of my favourite opamps is the OPA227. It has an offset of
75uV, is reasonable fast (8MHz, 2 V/us Slew Rate, but the OPA228
is faster), and runs off +/- 18 V max. It's a low cost opamp with
good characteristics, IMHO. But look out for its input bias, it
is around 10 or 100 nA.

That's > 10x what I want to pay! I could live with 100kHz GBWP - lol!
My idea of low cost is around 15 cents per dual op-amp in quantity!

Snork!

That's consumer product for you !
You want to see an itemised BOM ?

If you wish, but it'd be better to discuss your application and
circuit, to see why you need 0.1mV, and if there's a workaround
that'll allow you to use cheaper opamps.

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

Pooh Bear · May 18, 2005

Winfield Hill wrote:

Spehro Pefhany wrote...

On Tue, 17 May 2005, the renowned Pooh Bear wrote:

I have an application where I'm looking for a low input voltage offset
op-amp. I'd like 100uV or so typical and don't want to pay much. Lowish
input current is desirable too.

Speed isn't an issue, nor is very low noise or single supply operation.
In fact I *want* to run it off +/- 17V.

It's not an area I'm intimately familiar with.

There's no contest, use an OP-07D

TI's OP07DD, 60uV typ, 32.5 cents qty 2500, not bad, good call Spef!

--
Thanks,
- Win

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

Graham

Pooh Bear · May 18, 2005

Rock wrote:

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!

Astonishingly low offset.

Hmmm only 5V single rail though.

Graham

Pooh Bear · May 18, 2005

Joerg wrote:

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.

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

Pooh Bear · May 18, 2005

Jim Thompson wrote:

On Tue, 17 May 2005 23:54:43 GMT, Joerg
notthisjoergsch@removethispacbell.net> wrote:

Hello Jim,

Double-emitter choppers.

You're showing your age, John. And they weren't all that wonderful...
CMOS is MUCH better.

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

http://www.analogconsultants.com

Reminds me when we first met the daughter-in-law's family.

My son, bride-to-be and her mother show up in the bride's Honda Civic.

They say that father is on the way.

All of a sudden the house is shaking, and this crazy, hippy-looking
guy, with a bandanna, comes up the hill on a Harley chopper... so loud
that all the neighbors pour out of their houses.

It's the father-of-the-bride. Turns out he's a big-time dealer in
Harley parts in LA (now moved to Palm Springs).

Then he took off the bandanna... it had a velcro closure. I gave him
a ration of shit for lack of authenticity ;-)

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

Graham

Bill Sloman · May 18, 2005

"Jim Thompson" <thegreatone@example.com> schreef in bericht
news:v9ok819hvu2cv1mid03g28vvauou8tbcns@4ax.com...

On Tue, 17 May 2005 21:11:20 GMT, Joerg
notthisjoergsch@removethispacbell.net> wrote:

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

http://www.analogconsultants.com

Bill? Did I miss an actual technical contribution by Sloman ?

Since he's kill-filed me, he'll never know.

I love auto-zeroing.

Once upon a time, I even built a micro-voltmeter, using LM324's, to
measure voltage drop on PCB tracks, to locate shorts.

Zero, measure, zero, measure....

Haven't we all? Win has got a couple of pages on lock-in detection in "The
Art of Electronics" - it isn't exactly rocket science.

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

Winfield Hill · May 18, 2005

Bill Sloman wrote...

Jim Thompson wrote...
I love auto-zeroing.

Once upon a time, I even built a micro-voltmeter, using LM324's,
to measure voltage drop on PCB tracks, to locate shorts.

Zero, measure, zero, measure....

Haven't we all? Win has got a couple of pages on lock-in detection
in "The Art of Electronics" - it isn't exactly rocket science.

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

--
Thanks,
- Win

Spehro Pefhany · May 18, 2005

On Wed, 18 May 2005 09:09:00 +0100, the renowned Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:

Winfield Hill wrote:

Spehro Pefhany wrote...

On Tue, 17 May 2005, the renowned Pooh Bear wrote:

I have an application where I'm looking for a low input voltage offset
op-amp. I'd like 100uV or so typical and don't want to pay much. Lowish
input current is desirable too.

Speed isn't an issue, nor is very low noise or single supply operation.
In fact I *want* to run it off +/- 17V.

It's not an area I'm intimately familiar with.

There's no contest, use an OP-07D

TI's OP07DD, 60uV typ, 32.5 cents qty 2500, not bad, good call Spef!

--
Thanks,
- Win

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

Graham

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
--
"it's the network..." "The Journey is the reward"
speff@interlog.com Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog Info for designers: http://www.speff.com

Adrian Tuddenham · May 18, 2005

John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 17 May 2005 16:18:53 -0700, Jim Thompson
thegreatone@example.com> wrote:

On Tue, 17 May 2005 16:05:53 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 17 May 2005 15:43:53 -0700, Jim Thompson
thegreatone@example.com> wrote:

On Tue, 17 May 2005 15:12:11 -0700, John Larkin
jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

On Tue, 17 May 2005 21:48:26 GMT, Joerg
notthisjoergsch@removethispacbell.net> wrote:

Hello Jim,

Bill? Did I miss an actual technical contribution by Sloman ?

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

I love auto-zeroing.

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.

Once upon a time, I even built a micro-voltmeter, using LM324's, to
measure voltage drop on PCB tracks, to locate shorts.

Zero, measure, zero, measure....

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

Double-emitter choppers.

John

You're showing your age, John. And they weren't all that wonderful...
CMOS is MUCH better.

...Jim Thompson

Varicap parametric bridges.

John

What did they call the big-ass ones.

I vaguely remember using some kind of varactor to triple me up to the
2 meter band. (5W

...Jim Thompson

Burr-Brown did a very impressive potted-brick opamp using modulated
varicaps in the front end; CMRR was about infinite, as the entire
input circuit was transformer-coupled. I think Bob Pease did an
article on it. I seem to recall that TI did a monolithic varicap opamp
at some point... I may have a datasheet in The Dungeon.

Paramps are cool. Somebody did a paper on using ceramics caps as
active gain elements, and I have a paper on making nonlinear
transmission lines (shock lines) using the nonlinearity of ceramic
caps.

Just because I know about this stuff doesn't mean I'm old enough to
have experienced it all first-hand.

Pye made a pH meter with a mechanically driven varicap (like a tuning
fork) and an EF37A as the input valve (tube).

The input impedance was as near open circuit as a glass insulator can be
and the accuracy was totally dependent on the loop gain and the
super-high-stability resistors in the DC-coupled feedback loop.

It was a brilliant piece of design and could be configured with wire
links for different gains and offsets to suit various electrodes and
probes.

We had one still working in the labs when I left about 7 years ago.

--
~ Adrian Tuddenham ~
(Remove the ".invalid"s and add ".co.uk" to reply)
www.poppyrecords.co.uk

Jim Thompson · May 18, 2005

On 18 May 2005 04:36:51 -0700, Winfield Hill
<hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:

Bill Sloman wrote...

Jim Thompson wrote...
I love auto-zeroing.

Once upon a time, I even built a micro-voltmeter, using LM324's,
to measure voltage drop on PCB tracks, to locate shorts.

Zero, measure, zero, measure....

Haven't we all? Win has got a couple of pages on lock-in detection
in "The Art of Electronics" - it isn't exactly rocket science.

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

480)460-2350 | |
| E-mail Address at Website Fax

Keith Williams · May 18, 2005

In article <7vvie.898$kj7.554@newssvr21.news.prodigy.com>,
notthisjoergsch@removethispacbell.net says...

Hello Jim,

Double-emitter choppers.

You're showing your age, John. And they weren't all that wonderful...
CMOS is MUCH better.

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.

Before that they were what my grandmother put in the glass of water by

the side of the bed at night.

--
Keith

Jim Thompson · May 18, 2005

On 18 May 2005 04:36:51 -0700, Winfield Hill
<hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:

Bill Sloman wrote...

Jim Thompson wrote...
I love auto-zeroing.

Once upon a time, I even built a micro-voltmeter, using LM324's,
to measure voltage drop on PCB tracks, to locate shorts.

Zero, measure, zero, measure....

Haven't we all? Win has got a couple of pages on lock-in detection
in "The Art of Electronics" - it isn't exactly rocket science.

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

480)460-2350 | |
| E-mail Address at Website Fax

Joerg · May 18, 2005

Hello Keith,

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

And before that it described the folks that did what I just did:
Chopping the firewood for next winter. Or rather "farwood" in mountain
speak.

Regards, Joerg

http://www.analogconsultants.com

Joerg · May 18, 2005

Hello Graham,

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

Yes, although as said before the chopper concept also applies to certain
modifications of Harley Davidsons. And according to Keith also to the
third set of teeth.

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

That should be no big deal either. A very long time ago I needed that,
too, but at several MHz bandwidth. The project was on a tight BOM budget
(ain't that always so?) which is why I used a uA733. Everything else
either hadn't been invented yet or was way out of budget. The uA733 was
cheap and fast but didn't have any DC stability to write home about. So
I clamped differentially, using a FET.

The only downside was a wee charge injection. It wasn't much because
most of that went common mode. Still, I compensated for it by injecting
a similar opposite charge.

Regards, Joerg

http://www.analogconsultants.com

Winfield Hill · May 18, 2005

Jim Thompson wrote...

Winfield Hill wrote:
Bill Sloman wrote...
Jim Thompson wrote...

I love auto-zeroing.

Once upon a time, I even built a micro-voltmeter, using LM324's,
to measure voltage drop on PCB tracks, to locate shorts.

Zero, measure, zero, measure....

Haven't we all? Win has got a couple of pages on lock-in detection
in "The Art of Electronics" - it isn't exactly rocket science.

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

See... Newsgroups: alt.binaries.schematics.electronic
Subject: uV Meter with Auto Zero - AutoZeroNotes.pdf
Message-ID: <64om81l4gcikaqc3cjl51s8qmhcmt07974@4ax.com

Early '70's

My first precision autozero amplifier design was in 1965.

--
Thanks,
- Win

Favourite low offset op-amp

Rich Grise

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