Favourite low offset op-amp

[Joerg]

Hello Spehro,

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.

That is one of the marketing concepts I never really understood. I can't
even count anymore how often I have designed out such parts because they
were initially too expensive. Once the design-out process was completed
and tested the door went shut for them for good.

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

Switcher chips were probably the majority of chips I designed out, often
replacing them with a mundane sub-10c logic chip. Much of this is still
in production, likely never to be touched again.

Regards, Joerg

http://www.analogconsultants.com

 

[Keith Williams]

In article <vNKie.18566$J12.8767@newssvr14.news.prodigy.com>,
notthisjoergsch@removethispacbell.net says...

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.

....and your cutters of "farwoood" . As long as we're being complete,
what about them aeroplanes with wings that go roundy-round (the ones
banned from Italian airspace .

--
Keith

 

[Jim Thompson]

On 18 May 2005 10:31:47 -0700, Winfield Hill
<hill_a@t_rowland-dotties-harvard-dot.s-edu> wrote:

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.

Well if we're going to play, "Can you top this"... my MIT BSEE Thesis
(1961-1962) was done in cooperation with Harvard Med School, Peter
Bent Brigham Hospital (*) EKG Laboratory, with Doctors Gorlin, Hood,
Krasnow and Rolett, "Thermistors as Blood Flow Rate Transducers", and
featured a discrete chopper-stabilized operational amplifier made out
them thar new-fangled things called transistors ;-)

(*) Now called, I believe, Women and Children's ??

...Jim Thompson
--
| James E.Thompson, P.E. | mens |
| Analog Innovations, Inc. | et |
| Analog/Mixed-Signal ASIC's and Discrete Systems | manus |
| Phoenix, Arizona Voice480)460-2350 | |
| E-mail Address at Website Fax480)460-2142 | Brass Rat |
| http://www.analog-innovations.com | 1962 |

I love to cook with wine. Sometimes I even put it in the food.

 

[Pooh Bear]

bill.sloman@ieee.org wrote:

It wasn't exactly a new technique even then. My boss a George Kent
(1973-6) was proud of having replaced the relay choppers in the George
Kent chart recorder amplifiers with FET choppers.

The relays had - in their turn - replaced an ingenious mechanical
auto-zeroing system which was even slower.

Kent Instruments ? I recall the name.


Graham

 

[John Larkin]

On Thu, 19 May 2005 07:38:05 +0100, Pooh Bear
<rabbitsfriendsandrelations@hotmail.com> wrote:

bill.sloman@ieee.org wrote:

It wasn't exactly a new technique even then. My boss a George Kent
(1973-6) was proud of having replaced the relay choppers in the George
Kent chart recorder amplifiers with FET choppers.

The relays had - in their turn - replaced an ingenious mechanical
auto-zeroing system which was even slower.

Kent Instruments ? I recall the name.

The old tube-type Fluke differential voltmeters used vibrator choppers
and were very good. The worst part was the gas-tube voltage reference,
which you had to tweak against a standard cell fairly often as it
drifted around.

That reminds me, I should buy one on ebay for my collection. Nice
boxes with mirror-scale meters and lots of big fat knobs.


John

 

[Rich Grise]

On Wed, 18 May 2005 09:22:15 +0100, Pooh Bear wrote:

Jim Thompson wrote:

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 !

When I saw that one Beatle movie where one of them puts a Coca-Cola

bottle up to his nose, I was so young and naive I didn't even get
the joke. :-\

Cheers!
Rich

 

[Keith Williams]

In article <eldp815f832pvt1plk2kcv3067o45vilr5@4ax.com>,
jjlarkin@highNOTlandTHIStechnologyPART.com says...

On Thu, 19 May 2005 07:38:05 +0100, Pooh Bear
rabbitsfriendsandrelations@hotmail.com> wrote:

bill.sloman@ieee.org wrote:

It wasn't exactly a new technique even then. My boss a George Kent
(1973-6) was proud of having replaced the relay choppers in the George
Kent chart recorder amplifiers with FET choppers.

The relays had - in their turn - replaced an ingenious mechanical
auto-zeroing system which was even slower.

Kent Instruments ? I recall the name.



The old tube-type Fluke differential voltmeters used vibrator choppers
and were very good. The worst part was the gas-tube voltage reference,
which you had to tweak against a standard cell fairly often as it
drifted around.

In college I worked (and did the maintenance) on a pair of analog
computers with chopper-stabilized op-amps. This was '70-'74, but the
computers were at least a couple of decades older than that. After I
graduated no one knew how to use 'em and they were scrapped. :-(

That reminds me, I should buy one on ebay for my collection. Nice
boxes with mirror-scale meters and lots of big fat knobs.

--
Keith

 

[Bob Stephens]

On Thu, 19 May 2005 13:19:20 -0400, Keith Williams wrote:

In college I worked (and did the maintenance) on a pair of analog
computers with chopper-stabilized op-amps. This was '70-'74, but the
computers were at least a couple of decades older than that. After I
graduated no one knew how to use 'em and they were scrapped. :-(

Some of the older flight simulators I used to work on 1965 - 70 vintage
still used mechanical chopper stabilized opamps in the control loading
analog computers. The choppers were a little smaller than a C cell battery.
I forget the chopping frequency, but you could feel it switching through
the chopper's case.


Bob

 

[Keith Williams]

In article <1kb7df9050v28.ide2smal8ddf$.dlg@40tude.net>,
roberts@dcxchol.com says...

On Thu, 19 May 2005 13:19:20 -0400, Keith Williams wrote:

In college I worked (and did the maintenance) on a pair of analog
computers with chopper-stabilized op-amps. This was '70-'74, but the
computers were at least a couple of decades older than that. After I
graduated no one knew how to use 'em and they were scrapped. :-(

Some of the older flight simulators I used to work on 1965 - 70 vintage
still used mechanical chopper stabilized opamps in the control loading
analog computers. The choppers were a little smaller than a C cell battery.
I forget the chopping frequency, but you could feel it switching through
the chopper's case.

I guess I wasn't clear, but the analog computers (IIRC they were made
by Pace) above also used mechanical choppers (about the size of a 16oz.
beer can). One could hear them buzz, though I don't remember the
chopping frequency. Each chassis was about 10"x6"x18" and contained a
dual op amp or a servo-multiplier or servo-sine converter. One of the
computers had forty op amps and a dozen multipliers and sine
converters. The other was somewhat smaller.

--
Keith

 

[Joerg]

Hello Keith,

I guess I wasn't clear, but the analog computers (IIRC they were made
by Pace) above also used mechanical choppers (about the size of a 16oz.
beer can). ...

Why on earth did they use mechanical choppers? I mean, transistors had
been invented by then and in a differential and thermally coupled setup
the drift wasn't that bad.

Regards, Joerg

http://www.analogconsultants.com

 

[Keith Williams]

In article <ys5je.918$mK.648@newssvr13.news.prodigy.com>,
notthisjoergsch@removethispacbell.net says...

Hello Keith,

I guess I wasn't clear, but the analog computers (IIRC they were made
by Pace) above also used mechanical choppers (about the size of a 16oz.
beer can). ...

Why on earth did they use mechanical choppers? I mean, transistors had
been invented by then and in a differential and thermally coupled setup
the drift wasn't that bad.

Well, each op-amp was something like a dozen tubes, so I don't think
they quite had transistors down at that point (built in the '50s).
IIRC the open-loop gain of the amplifiers was 1E8, or some such. The
computers were designed for four-digit accuracy.

--
Keith

 

[Spehro Pefhany]

On Thu, 19 May 2005 19:06:06 GMT, the renowned Joerg
<notthisjoergsch@removethispacbell.net> wrote:

Hello Keith,

I guess I wasn't clear, but the analog computers (IIRC they were made
by Pace) above also used mechanical choppers (about the size of a 16oz.
beer can). ...

Why on earth did they use mechanical choppers? I mean, transistors had
been invented by then and in a differential and thermally coupled setup
the drift wasn't that bad.

Early transistor thermocouple and strain-guage amplifiers used
mechanical choppers too. IIRC they were more like the size of a vacuum
tube, but that was a very long time ago and I were a mere wisp of a
lad.


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

 

[Rich Grise]

On Thu, 19 May 2005 19:06:06 +0000, Joerg wrote:

Hello Keith,

I guess I wasn't clear, but the analog computers (IIRC they were made
by Pace) above also used mechanical choppers (about the size of a 16oz.
beer can). ...

Why on earth did they use mechanical choppers? I mean, transistors had
been invented by then and in a differential and thermally coupled setup
the drift wasn't that bad.

1) Known reliability
2) If it works, why fix it?

I had a buddy once who was a "Simulator Engineer" at what was then
Republic Airlines, in MSP. He worked 3rd shift, so he'd let friends
come over and fly the DC-9 simulator. It was one of those ones in
the two-story high room, on the six 6' hydraulic struts, and four
HUGE TV screens outside the windows. Kind of like this one:
http://www.simlabs.arc.nasa.gov/cvsrf/images/acfs_sim.jpg
I found that a DC-9 doesn't respond quite as snappily to control inputs
as a Cessna 150. But you could do a barrel-roll in it, except it
would go to about 45 degrees of bank, hit the stops, and when the math
model got all the way around to about 45 degrees of bank the other way, it
went WHAP! to the other side, and bonked your head against the side wall.

Landing it was really weird. When you flare, you practically have to
drive it into the ground, or ground effects would float it off the
end of the runway, or at least that's what it felt like.

It had a TI processor with 64K bytes of memory.

He often said that he'd like to get ahold of some fighter jet math model,
but I don't know if that ever materialized.

Cheers!
Rich

 

[Bob Monsen]

Rich Grise wrote:

On Thu, 19 May 2005 19:06:06 +0000, Joerg wrote:


Hello Keith,


I guess I wasn't clear, but the analog computers (IIRC they were made
by Pace) above also used mechanical choppers (about the size of a 16oz.
beer can). ...

Why on earth did they use mechanical choppers? I mean, transistors had
been invented by then and in a differential and thermally coupled setup
the drift wasn't that bad.


1) Known reliability
2) If it works, why fix it?

I had a buddy once who was a "Simulator Engineer" at what was then
Republic Airlines, in MSP. He worked 3rd shift, so he'd let friends
come over and fly the DC-9 simulator. It was one of those ones in
the two-story high room, on the six 6' hydraulic struts, and four
HUGE TV screens outside the windows. Kind of like this one:
http://www.simlabs.arc.nasa.gov/cvsrf/images/acfs_sim.jpg
I found that a DC-9 doesn't respond quite as snappily to control inputs
as a Cessna 150. But you could do a barrel-roll in it, except it
would go to about 45 degrees of bank, hit the stops, and when the math
model got all the way around to about 45 degrees of bank the other way, it
went WHAP! to the other side, and bonked your head against the side wall.

There is a great story about the test pilot for the boeing 707, on the
introduction to the public. Here is a video that describes it:

http://www.aviationexplorer.com/707_roll_video.htm

 

[keith]

On Thu, 19 May 2005 16:53:52 -0700, Bob Monsen wrote:

Rich Grise wrote:
On Thu, 19 May 2005 19:06:06 +0000, Joerg wrote:


Hello Keith,


I guess I wasn't clear, but the analog computers (IIRC they were made
by Pace) above also used mechanical choppers (about the size of a 16oz.
beer can). ...

Why on earth did they use mechanical choppers? I mean, transistors had
been invented by then and in a differential and thermally coupled setup
the drift wasn't that bad.


1) Known reliability
2) If it works, why fix it?

I had a buddy once who was a "Simulator Engineer" at what was then
Republic Airlines, in MSP. He worked 3rd shift, so he'd let friends
come over and fly the DC-9 simulator. It was one of those ones in
the two-story high room, on the six 6' hydraulic struts, and four
HUGE TV screens outside the windows. Kind of like this one:
http://www.simlabs.arc.nasa.gov/cvsrf/images/acfs_sim.jpg
I found that a DC-9 doesn't respond quite as snappily to control inputs
as a Cessna 150. But you could do a barrel-roll in it, except it
would go to about 45 degrees of bank, hit the stops, and when the math
model got all the way around to about 45 degrees of bank the other way, it
went WHAP! to the other side, and bonked your head against the side wall.


There is a great story about the test pilot for the boeing 707, on the
introduction to the public. Here is a video that describes it:

http://www.aviationexplorer.com/707_roll_video.htm

The amazing thing abut that is that the aircraft never new it was
upside-down. It was a perfect 1G roll (no change in the gravity vector).
It was impressive to see, though not so once the physics are understood.
"Tex" Johnson was "suspended" (he ws reinstated after promising never
to do it again) for doing something "that dangerous", but the Dash-80 (the
707 prototype) didn't care a bit.

--
Keith

 

[Mark Zenier]

In article <amvk811tuk6n43f3h870tejs6j09hh6rn6@4ax.com>,
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:

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.

Philbrick.

"The Story of the P2"...

Chapter 9 in _Analog Circuit Design: Art, Science, Personalities_


Mark Zenier mzenier@eskimo.com Washington State resident

 

[John Larkin]

On Fri, 20 May 2005 20:35:05 GMT, mzenier@eskimo.com (Mark Zenier)
wrote:

In article <amvk811tuk6n43f3h870tejs6j09hh6rn6@4ax.com>,
John Larkin <jjlarkin@highNOTlandTHIStechnologyPART.com> wrote:
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.


Philbrick.

Right.

John