AoE x-Chapters, High-Speed op-amps section, DRAFT

On Friday, April 26, 2019 at 6:37:15 PM UTC-4, tabb...@gmail.com wrote:
On Friday, 26 April 2019 22:02:28 UTC+1, John Larkin wrote:
On Fri, 26 Apr 2019 13:11:46 -0400, Phil Hobbs

LM324. ;)

The horror!


National used to make a combo LM358/LM393 amp/comparator. (LM611 and
614 maybe?)

IIRC JT said that the two were the same silicon with different
metallization.

But for slow stuff that has to be very cheap, using a section of a 324
as a comparator works fine.

Cheers

Phil Hobbs

One thing about the classic National LM324 is that if you rail any
section, it wrecks the shared bias supplies for the other sections. So
one comparator switching *really* messes up whatever the other three
amps are doing.

I think some peoples' later versions didn't do that.

The 324 is my favourite opamp ever. You get so much for so little.


NT

Huh, I never used it. I might have replaced some.
I guess that's my loss.
What's 'so much' ?

George H.
(I use more opa2134's than anything else.)
 
"George Herold" <gherold@teachspin.com> wrote in message
news:4abe756c-3c8a-4ea5-9f95-22a46b4d06d9@googlegroups.com...
The 324 is my favourite opamp ever. You get so much for so little.


Huh, I never used it. I might have replaced some.
I guess that's my loss.
What's 'so much' ?

Distortion is "so much". The output stage is class B so exhibits crossover
distortion unless you bias it. Among other quirks that some are
suspiciously quick to forget... :)

I'm partial to TLV2372 myself.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/
 
Joerg wrote:
1. EMI behavior of opamps. This is generally not understood at all by
engineers and (still!) not taught at universities from what young EEs
told me. A bipolar input stage will rectify RF at the first BE
junction, even stuff at cell phone frequencies. This rectification or
demodulation is very inefficient but since that is inside the loop
any resultying baseband AM will hit at full tilt because it happens
at "open loop".
This has brought me several consulting assigments so maybe don't add
it. OTOH I am trying to retire, so maybe put it in, so I can cycle
more, bike more and brew more beer.

No kidding, two weeks ago I explained that to two engineers at a
client and they went "WHAT?!". Many don't believe it until
demonstrated.
[...]

What's needed is a circuit to provide the demonstration. I asked for
something like that pertaining to some other phenomenon, but even if
it's more appropriate for the lab book it should be somewhere,
especially in a case where, as you say, people need proof.
 
On Fri, 26 Apr 2019 15:37:12 -0700 (PDT), tabbypurr@gmail.com wrote:

On Friday, 26 April 2019 22:02:28 UTC+1, John Larkin wrote:
On Fri, 26 Apr 2019 13:11:46 -0400, Phil Hobbs

LM324. ;)

The horror!


National used to make a combo LM358/LM393 amp/comparator. (LM611 and
614 maybe?)

IIRC JT said that the two were the same silicon with different
metallization.

But for slow stuff that has to be very cheap, using a section of a 324
as a comparator works fine.

Cheers

Phil Hobbs

One thing about the classic National LM324 is that if you rail any
section, it wrecks the shared bias supplies for the other sections. So
one comparator switching *really* messes up whatever the other three
amps are doing.

I think some peoples' later versions didn't do that.

The 324 is my favourite opamp ever. You get so much for so little.


NT

You get a lot. Offset, noise, crossover distortion, amplifier
interaction, thermal self-destruction, and really interesting behavior
if any input is pulled a few tenths of a volt below ground.

ESD tolerance is spec'd at 250 volts!




--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On Fri, 26 Apr 2019 19:51:00 -0500, "Tim Williams"
<tiwill@seventransistorlabs.com> wrote:

"George Herold" <gherold@teachspin.com> wrote in message
news:4abe756c-3c8a-4ea5-9f95-22a46b4d06d9@googlegroups.com...

The 324 is my favourite opamp ever. You get so much for so little.


Huh, I never used it. I might have replaced some.
I guess that's my loss.
What's 'so much' ?

Distortion is "so much". The output stage is class B so exhibits crossover
distortion unless you bias it. Among other quirks that some are
suspiciously quick to forget... :)

I've seen visible crossover distortion amplifying a 60 Hz sine wave.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
On Fri, 26 Apr 2019 07:10:37 -0700, Winfield Hill wrote:

Allan Herriman wrote...

On Wed, 24 Apr 2019 17:19:53 -0700, John Miles, KE5FX wrote:

On Wednesday, April 24, 2019 at 4:04:34 AM UTC-7, Winfield Hill wrote:
Read and comment. AoE x-Chapters,

You might add the LMH6733 to your table. 3 wideband CFB amps with
shutdown pins, somewhat similar to OPA3695.

Also could be worth mentioning that the shutdown pins on many of these
parts are referenced to the positive rail, not ground. That just
hosed me the other day. The shutdown pin on the LMH6733 and similar
parts is best thought of as an analog input, not a digital one.
Some chips like the newer THS3491 have a separate reference pin just
for that purpose, but most don't. For the LMH6733 the disable/enable
thresholds are specified at 3.2V and 3.6V for 5V rails, and you need
to add a volt to them if you max out the rails at +/- 6 volts.

That could be (and was) a problem when relying on an open-drain output
to pull the shutdown pin up to 5 volts, since the current drawn by the
shutdown pin is not negligible. (Worse, the open-drain pin in
question was on an I2C extender whose data sheet specifies 5.5V
compatibility at the GPIO pins without regard to its own supply
voltage, but didn't mention the ESD diode that limits the "open drain"
voltage to 1 volt above the Vdd rail, which was 3.3V in my case.)

-- john, KE5FX

LTC6228 has a multifunction shutdown pin. Different voltages (wrt the
positive rail) will shutdown the whole opamp, or enable / disable the
input bias current cancellation circuit (allowing one to trade input
current noise for input bias current).

Wow, Allan, that's one fascinating op-amp. It's new and I had missed
it, thanks!

For me, the fascination is why they thought a sub-nV/rtHz opamp would be
marketable with a 1/f noise corner so high.

Perhaps I misunderstood the intended application.

Allan
 
On Saturday, 27 April 2019 01:40:56 UTC+1, George Herold wrote:
On Friday, April 26, 2019 at 6:37:15 PM UTC-4, tabby wrote:

The 324 is my favourite opamp ever. You get so much for so little.

Huh, I never used it. I might have replaced some.
I guess that's my loss.
What's 'so much' ?

George H.
(I use more opa2134's than anything else.)

Now there's an impractically broad question :)


NT
 
On Saturday, 27 April 2019 01:51:09 UTC+1, Tim Williams wrote:
"George Herold" <gherold@teachspin.com> wrote in message
news:4abe756c-3c8a-4ea5-9f95-22a46b4d06d9@googlegroups.com...
NT

The 324 is my favourite opamp ever. You get so much for so little.


Huh, I never used it. I might have replaced some.
I guess that's my loss.
What's 'so much' ?

Distortion is "so much". The output stage is class B so exhibits crossover
distortion unless you bias it. Among other quirks that some are
suspiciously quick to forget... :)

I'm partial to TLV2372 myself.

Tim

It's not hard to avoid distortion.
Quirks must be remembered with every IC or circuit.


NT
 
On Saturday, 27 April 2019 02:54:29 UTC+1, John Larkin wrote:
On Fri, 26 Apr 2019 15:37:12 -0700 (PDT), tabbypurr wrote:
On Friday, 26 April 2019 22:02:28 UTC+1, John Larkin wrote:
On Fri, 26 Apr 2019 13:11:46 -0400, Phil Hobbs

LM324. ;)

The horror!


National used to make a combo LM358/LM393 amp/comparator. (LM611 and
614 maybe?)

IIRC JT said that the two were the same silicon with different
metallization.

But for slow stuff that has to be very cheap, using a section of a 324
as a comparator works fine.

Cheers

Phil Hobbs

One thing about the classic National LM324 is that if you rail any
section, it wrecks the shared bias supplies for the other sections. So
one comparator switching *really* messes up whatever the other three
amps are doing.

I think some peoples' later versions didn't do that.

The 324 is my favourite opamp ever. You get so much for so little.

You get a lot. Offset, noise, crossover distortion, amplifier
interaction, thermal self-destruction, and really interesting behavior
if any input is pulled a few tenths of a volt below ground.

ESD tolerance is spec'd at 250 volts!

The main thing you get is cheap.
ALL opamps have offset & noise. Other low cost opamps aren't significantly different to the 324 in that respect.
FWIW its prime limitation is slew rate.
There's no end of applications that don't run into any problems with it - that's why it's so common in consumer equipment. You of course are in a different market.


NT
 
On Sat, 27 Apr 2019 05:53:30 -0700 (PDT), tabbypurr@gmail.com wrote:

On Saturday, 27 April 2019 02:54:29 UTC+1, John Larkin wrote:
On Fri, 26 Apr 2019 15:37:12 -0700 (PDT), tabbypurr wrote:
On Friday, 26 April 2019 22:02:28 UTC+1, John Larkin wrote:
On Fri, 26 Apr 2019 13:11:46 -0400, Phil Hobbs

LM324. ;)

The horror!


National used to make a combo LM358/LM393 amp/comparator. (LM611 and
614 maybe?)

IIRC JT said that the two were the same silicon with different
metallization.

But for slow stuff that has to be very cheap, using a section of a 324
as a comparator works fine.

Cheers

Phil Hobbs

One thing about the classic National LM324 is that if you rail any
section, it wrecks the shared bias supplies for the other sections. So
one comparator switching *really* messes up whatever the other three
amps are doing.

I think some peoples' later versions didn't do that.

The 324 is my favourite opamp ever. You get so much for so little.

You get a lot. Offset, noise, crossover distortion, amplifier
interaction, thermal self-destruction, and really interesting behavior
if any input is pulled a few tenths of a volt below ground.

ESD tolerance is spec'd at 250 volts!


The main thing you get is cheap.
ALL opamps have offset & noise. Other low cost opamps aren't significantly different to the 324 in that respect.
FWIW its prime limitation is slew rate.
There's no end of applications that don't run into any problems with it - that's why it's so common in consumer equipment. You of course are in a different market.


NT

I design almost exclusively with single SOT23 or SO8 amps. The PCB
layouts are much nicer than with duals or quads.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
Joerg wrote:
1. EMI behavior of opamps. This is generally not understood at all by
engineers and (still!) not taught at universities from what young EEs
told me. A bipolar input stage will rectify RF at the first BE
junction, even stuff at cell phone frequencies. This rectification or
demodulation is very inefficient but since that is inside the loop
any resultying baseband AM will hit at full tilt because it happens
at "open loop".

Why only with opamps? Do you also get that effect in some transistor
amps?
 
On 26 Apr 2019 17:29:52 -0700, Winfield Hill
<hill@rowland.harvard.edu> wrote:

John Larkin wrote...

On 26 Apr 2019, Winfield Hill wrote:

John Larkin wrote...

One thing about the classic National LM324 is that
if you rail any section, it wrecks the shared bias
supplies for the other sections.

I remember JT claiming that was the designer's
fault, we should never let an opamp saturate.

Single SOT23 opamps don't have a shared bias supply problem!

Yes, but it's trivial to add one transistor, and
circumvent the problem. I felt we should blame Jim,
rather than have him blaming us for our standard use.

What would that transistor do?

Seems easier to buy a decent opamp than to kluge a bad one.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
On Wed, 24 Apr 2019 12:35:55 -0700, Joerg <news@analogconsultants.com>
wrote:

On 2019-04-24 04:04, Winfield Hill wrote:
Read and comment. AoE x-Chapters,
High-Speed op-amps section, DRAFT.

Recall, the AoE x-Chapters are advanced material that
was meant to come after each relevant chapter, can skip
on a quick first read, go back later for detailed info.
But as main book was growing over 2000 pages, we opted to
bring out main book first, including x-Chapter cross refs,
follow with x-Chapter book. As explained in the preface.

26 pages of good stuff, from new sections 4x.5 and 4x.6
Chapter 4x is to supplement H&H AoE III, chapters 4,5,8.
(Full Chapter 4x is now 146 pages long, still growing.)

DRAFT, but getting close to being complete.

Are explanations excellent, good, OK, or confusing?
Examine tables, any of your favorite parts missing?**
Want a separate low-power table? Can we skip that?
Is the CFB op-amp scene explained well enough?
Did you like VFB scatterplots? Need some for CFB?
Have a favorite trick that should be included?
Make comments here or send to winfieldhill@yahoo.com

https://www.dropbox.com/s/aemtyly16mtj87n/Op-amps_High-speed_ch4x_DRAFT.pdf?dl=0

** For op-amps that come in multiple variants, i.e.,
single, dual, quad, we list only one part, and show
# per pkg variants in next column, so you may not see
your part, e.g., we show OPA192, not OPA2192 or OPA4192.
As you can see, we were forced to economize on space.


Pretty good.

Two suggested additions:


1. EMI behavior of opamps. This is generally not understood at all by
engineers and (still!) not taught at universities from what young EEs
told me. A bipolar input stage will rectify RF at the first BE junction,
even stuff at cell phone frequencies. This rectification or demodulation
is very inefficient but since that is inside the loop any resultying
baseband AM will hit at full tilt because it happens at "open loop".

This has brought me several consulting assigments so maybe don't add it.
OTOH I am trying to retire, so maybe put it in, so I can cycle more,
bike more and brew more beer.

No kidding, two weeks ago I explained that to two engineers at a client
and they went "WHAT?!". Many don't believe it until demonstrated. GSM
phones are good for doing that, when they connect to a new tower.
Switching to a CMOS opamp usually makes that problem go away 100%. When
I did that for the first time I almost achieved guru-status at that
client because nobody had ever fixed an EMC issue without a serious
re-layout there.


2. Back-to-back input protection diodes between IN+ and IN-. Very often
overlooked. In datasheets they are sometimes only mentioned in a
footnote under the abs max table but often there is only a +/-0.3V diff
limit. Aside from pouring gasoline on the above mentioned EMI issue
these diodes can really throw people a curve when using opamps in an
unorthodox way or as a comparator. Thou shalt not do that but ...

Here's an EMI fix for the front end of a diffamp, 16x on a VME module.

https://www.dropbox.com/s/n9yv10rzza8e66a/V490_EMI_Adapter.JPG?dl=0

The customer was seeing EMI from an adjacent CPU module that was
causing 10 or so LSB offsets in a 16-bit ADC. The adapter allows an
emi hard amp, ADA4522, to go into the weird footprint of an LT1124.
The 1124 is a great RF detector.

The customer wanted to pay us to fix our EMI problem.

This is incidentally pretty much the circuit in AoE3 p 361.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
John Larkin wrote...
On 26 Apr 2019, Winfield Hill wrote:

Yes, but it's trivial to add one transistor, and
circumvent the problem. I felt we should blame Jim,
rather than have him blaming us for our standard use.

What would that transistor do?

I thought it was in AoE-III, but it was one of the
"advanced" things that got moved to the x-Chapters,
when we thought they were still going to be part
of the main book. Sorry. Here's a link:

https://www.dropbox.com/s/gburz2nrfpdqvri/mirror_with-extra-BJT.JPG?dl=0

Seems easier to buy a decent opamp than to kluge
a bad one.

That extra transistor isn't a kludge, and I'll
bet it's actually in most modern op-amps, etc.


--
Thanks,
- Win
 
On 27/04/2019 17:50, Winfield Hill wrote:
I thought it was in AoE-III, but it was one of the
"advanced" things that got moved to the x-Chapters,
when we thought they were still going to be part
of the main book. Sorry. Here's a link:

https://www.dropbox.com/s/gburz2nrfpdqvri/mirror_with-extra-BJT.JPG?dl=0

That is truly *beautiful* - wonderfully elegant.

Thanks Win, not seen that before.

piglet
 
"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message
news:sid7ce5hbeotn45ap3buoa1d6tnolkmf7v@4ax.com...
I've seen visible crossover distortion amplifying a 60 Hz sine wave.

I like to put it this way: it's noticeable even in a control loop.

Tim

--
Seven Transistor Labs, LLC
Electrical Engineering Consultation and Design
Website: https://www.seventransistorlabs.com/
 
On Sat, 27 Apr 2019 12:54:22 -0500, "Tim Williams"
<tiwill@seventransistorlabs.com> wrote:

"John Larkin" <jjlarkin@highlandtechnology.com> wrote in message
news:sid7ce5hbeotn45ap3buoa1d6tnolkmf7v@4ax.com...
I've seen visible crossover distortion amplifying a 60 Hz sine wave.


I like to put it this way: it's noticeable even in a control loop.

Tim

You should be happy to pay extra for integrated deadband.

Actually, it's professional malpractice to use an LM324 in a control
loop.


--

John Larkin Highland Technology, Inc
picosecond timing precision measurement

jlarkin att highlandtechnology dott com
http://www.highlandtechnology.com
 
Piglet wrote...
On 27/04/2019 17:50, Winfield Hill wrote:

I thought it was in AoE-III, but it was one of the
"advanced" things that got moved to the x-Chapters,
when we thought they were still going to be part
of the main book. Sorry. Here's a link:

https://www.dropbox.com/s/gburz2nrfpdqvri/mirror_with-extra-BJT.JPG?dl=0

That is truly *beautiful* - wonderfully elegant.
Thanks Win, not seen that before.

Yes, it's simple and obvious once you see it.
It's hopefully in most ICs with shared mirrors,
although simplified schematics may not show it.


--
Thanks,
- Win
 
On 27 Apr 2019 09:50:44 -0700, Winfield Hill
<hill@rowland.harvard.edu> wrote:

John Larkin wrote...

On 26 Apr 2019, Winfield Hill wrote:

Yes, but it's trivial to add one transistor, and
circumvent the problem. I felt we should blame Jim,
rather than have him blaming us for our standard use.

What would that transistor do?

I thought it was in AoE-III, but it was one of the
"advanced" things that got moved to the x-Chapters,
when we thought they were still going to be part
of the main book. Sorry. Here's a link:

https://www.dropbox.com/s/gburz2nrfpdqvri/mirror_with-extra-BJT.JPG?dl=0

Seems easier to buy a decent opamp than to kluge
a bad one.

That extra transistor isn't a kludge, and I'll
bet it's actually in most modern op-amps, etc.

Sorry, I thought you meant to add an external transistor somehow.

Transistors are so cheap in an IC, why share current mirrors between
opamp sections?

LM324 is ancient, full of hazards.


--

John Larkin Highland Technology, Inc

lunatic fringe electronics
 
lørdag den 27. april 2019 kl. 20.09.02 UTC+2 skrev piglet:
On 27/04/2019 17:50, Winfield Hill wrote:

I thought it was in AoE-III, but it was one of the
"advanced" things that got moved to the x-Chapters,
when we thought they were still going to be part
of the main book. Sorry. Here's a link:

https://www.dropbox.com/s/gburz2nrfpdqvri/mirror_with-extra-BJT.JPG?dl=0


That is truly *beautiful* - wonderfully elegant.

Thanks Win, not seen that before.

piglet

https://wiki.analog.com/university/courses/electronics/text/chapter-11#buffered_feedback_current_mirror

?
 

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