Favourite low offset op-amp

[Pooh Bear]

Hi all,

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.

Anyone got any suggestions ? Low cost remember !


Cheers, Graham

 

[Pooh Bear]

Pooh Bear a écrit :



One of my favourite opamps is the OPA227. It has an offset of < 75 uV,
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 !


Graham

 

[[email protected]]

Pooh Bear a écrit :

Hi all,

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.

Anyone got any suggestions ? Low cost remember !


Cheers, Graham

One of my favourite opamps is the OPA227. It has an offset of < 75 uV,
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.

Best,
Bernhard

 

[[email protected]]

Sounds like a job for an auto-zeroing op amp. Linear Technology have
been making them for many years, though National Semiconductor and
Analog Devices also introduced useful products some years ago.

+/-17V is a bit high for this sort of amplifier - the Linear Technology
LTC1150 is the only one I know of that comes close, with a maximum
supply voltage of +/-16V. It isn't cheap - at about $5 in small
quantities, while the lower supply voltage parts come in under a
dollar. and the input currents aren't all that low, at around a
nanoamp, while the lower supply voltage parts claim tens of picoamps,
but the input offset voltage is 0.5uV typical, +/-10uV worst case.

 

[Winfield Hill]

Pooh Bear (Graham) wrote...

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!

 

[Pooh Bear]

Pooh Bear (Graham) wrote...

Snork!

That's consumer product for you !

You want to see an itemised BOM ?

Graham

 

[Winfield Hill]

Pooh Bear wrote...

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.

 

[Spehro Pefhany]

Hi all,

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.

Anyone got any suggestions ? Low cost remember !


Cheers, Graham

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



Best regards,
Spehro Pefhany

 

[Winfield Hill]

Spehro Pefhany wrote...

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

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

 

[John Larkin]

Snork!

Is that term in the Dictionary of Electronics?

John

 

[Joerg]

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

 

[Joerg]

Hello Winfield,

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.

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

 

[Jim Thompson]

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

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

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....

...Jim Thompson

 

[Joerg]

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.

Regards, Joerg

 

[Jim Thompson]

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.

Ah, yes. DC restorers. I grew up in a radio/TV repair shop ;-)

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

Regards, Joerg

I used 'HC4016's to do the work. Actually left out a step above,
should be...

Zero, measure, hold, zero, measure, hold....

With non-overlap between each, to keep caps from getting tweaked.

...Jim Thompson

 

[Spehro Pefhany]

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.

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


Best regards,
Spehro Pefhany

 

[John Larkin]

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.

Double-emitter choppers.

John

 

[martin griffith]

On 17 May 2005 03:59:34 -0700, Winfield Hill


Is that term in the Dictionary of Electronics?

John

Tis now


martin

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

 

[Jim Thompson]

Double-emitter choppers.

John

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

...Jim Thompson

 

[John Larkin]

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

...Jim Thompson

Varicap parametric bridges.

John