EEVblog #600 - Opamps Explained

[w2aew]

Very glad to see Dave's video on this topic, and even happier to see that he used the same basic approach and examples in his video as I did in my video on the same topic.  Of course, I didn't go into the same level of detail in my 14 minute video.  This video has been the most-viewed video on my channel for a while, so I'm sure that Dave's is going to surpass mine in total views very shortly.

Here's my video from about a year ago:

[Legion]

Very glad to see Dave's video on this topic, and even happier to see that he used the same basic approach and examples in his video as I did in my video on the same topic.  Of course, I didn't go into the same level of detail in my 14 minute video.  This video has been the most-viewed video on my channel for a while, so I'm sure that Dave's is going to surpass mine in total views very shortly.

Here's my video from about a year ago:

Thanks for the video. I enjoyed it. U ar uh gud teechur n enjinere! 

[Pasky]

This is probably one of my favorite videos to date now, I learned a lot watching this one, thanks a lot.

[hikariuk]

Audiophiles will use undefined terms such as "colour", "brightness", "danceable", "sonic redemption", "space clarity", "well-tempered personality" etc. to describe components.

Which is kind of amusing because "well-tempered" actually means something in music: it's a type of tuning.

[sergey]

Great video, Dave!

And yes, thumbs up for the proper opamp termination video

[sergey]

For those of you who may not know just how far we have come with OpAmps....here's a great read from Analog Devices. I just love reading the history. It makes me appreciate all those great pioneers back in the day when OpAmps were the best things since the vacuum tube

https://dl.dropboxusercontent.com/u/6757916/ADI%20opamp%20classic.pdf

Enjoy!

That's really great reading, thanks for sharing the paper with us!

[Frink42]

Audiophiles will use undefined terms such as "colour", "brightness", "danceable", "sonic redemption", "space clarity", "well-tempered personality" etc. to describe components.

The terms can mean nearly anything.

Fun fact: simply moving a couple of inches in your seat is enough to disrupt any audio comparison due to the "comb effect". So it's very hard to accurately compare any audio system.  A well designed amplifier will do nothing audible to the signal; the rest is up to the listener, and often the headphones or speakers, which introduce tons more distortion than any electronic part does.

Audiophiles simply aren't consistent with what they want/mean. A perfectly designed amplifier using an op-amp will sound "cold" and probably "harsh" even though it doesn't distort at all. Then, they will use a valve amp "because it sounds better", when all it really does is adding distortion heh. All in all, sound quality is subjective.

It would be fun to know which kind of distortion is percieved as "good".

[mrflibble]

For those of you who may not know just how far we have come with OpAmps....here's a great read from Analog Devices. I just love reading the history. It makes me appreciate all those great pioneers back in the day when OpAmps were the best things since the vacuum tube

https://dl.dropboxusercontent.com/u/6757916/ADI%20opamp%20classic.pdf

Enjoy!

And when that dropbox url goes poof, you can still download it from AD: http://www.analog.com/library/analogdialogue/archives/39-05/web_chh_final.pdf

[Rutger]

What is the most versatile jelly bean op-amp a hobbyists should have in his/her toolkit?

[vieirae]

Hi Dave
Great video on OpAmps!
Would it be possible to explain the functionning of Norton current-based OpAmps. When would the use of
such devices make sense (current regulation instead of voltage)? Or is it always better to regulate current
by regulating voltage over a resistor using a "classical" OpAmp?

[David Hess]

What is the most versatile jelly bean op-amp a hobbyists should have in his/her toolkit?

If I count cost than probably the 324/358 but my personal preference is for low input current bipolar operational amplifiers like the LT1008, LT1012, or LT1097 which support external compensation or overcompensation.  If I needed single supply operation, then the LT1006 would be my choice.

[calin]

That is exactly what hapenned to me few weeks ago .. the  damn step occurring at zero crossing     ... that same exact note got me out of it. Go figure ... "[size=78%]The LM358 will operate satisfactorily in balanced supply operation so long as a load is maintained from[/size]
output to the negative supply." Perfect case of headbanging for electronics morons like me    at leas t I am good enough @ googeling 

The challenge question addressed. AN-116 answers it. Application notes are typically where IC vendors CTA ( cover their as*) and the first place to find those  "gotchas" 

http://www.ti.com/lit/an/snoa662b/snoa662b.pdf . See page 6.

Nice curve ball, Dave!

[David Hess]

That is exactly what hapenned to me few weeks ago .. the  damn step occurring at zero crossing     ... that same exact note got me out of it. Go figure ... "[size=78%]The LM358 will operate satisfactorily in balanced supply operation so long as a load is maintained from[/size]
output to the negative supply." Perfect case of headbanging for electronics morons like me    at leas t I am good enough @ googeling 

The challenge question addressed. AN-116 answers it. Application notes are typically where IC vendors CTA ( cover their as*) and the first place to find those  "gotchas" 

http://www.ti.com/lit/an/snoa662b/snoa662b.pdf . See page 6.

Nice curve ball, Dave!

The improved LM358/LM324 operational amplifiers like the LT1013/LT1014 have class AB output stages so do not suffer from that particular problem.

[sportq]

PLEASE don't even suggest using opamps as comparators to newbies, or they might actually think it is okay and you know full well that it is not okay.

It seems ok for HP/Agilent/Keysight, this is from page 129 of the E3631A  schematic (a current product). U6 is an OP27 used as a comparator.

Pete

[mexakin]

Hello,
i do really like those fundamentals about OpAmp and everythign surrounding it, since practical issues you cannot learn from a textbook but need experience or listen to someone who got expirience. I did not yet watch this episode. But just want to contribute, since I am into doing analog digital design since 4 years now, and I did read and build a whole lot sensors, mostly transimpedance stuff, where inbut bias currents hit you pretty well, due to the huge gain you have to achieve, but anyway, what I did want to recommend for those who wanna learn more about OpAmps and their history:

I did read Bo Lijeks: Semiconductor History, pretty nice book also packed with a lot of anecdotes and stories not so much about Opamps but semicondurctor in general ( it has a whole chapter on Bob Widlar as well, which befor I didnt even notice, and I did study electronics enigneering so I guess probably less than 20% of all student know him after their diploma , which is kind of sad since he and his surround works really puts some life into some rather dusty studies)

The AnalogDevice *pfd is really readable as well, but what really did strike me is Hans Cammenzids little book about analog chips, for those who didnt know ( as myself) he is the inventor of the 555-Timer ( which Dave also did a episode about some month ago) and his book is really awesome to read, it explains everything in a very down to earth approach, its not packed with formula but with hands on data, so dont expect to really learn how, but rather understand why the OpAmp and semiconductors evolution took place and why we got OpAmps and their internal structure right now. Adn this is also explained in semiconductor levels , liek why is it important to not design big resitance in semiconductor material and so on, and on.

http://www.designinganalogchips.com/
The book should be available free to download, his other book about the history of electron is also really interesting, I did read it as I read a lot bibliographies about guys involved with electrons, I like it to see how things evolve and those books pretty much do it.

And the last source is Analog circuit design by Jim Williams, it is a collection of big analog designers telling a lot of different stories about their life their thoughts about design, some talk about OpAmps, others about who to become an analoge designer, I think even Philbrick tells the story about his first OpAmp.

http://books.google.de/books?id=CFoEAP2lwLEC&pg=PR4&lpg=PR4&dq=ISBN+0-7506-9+166-2&source=bl&ots=4rnvpNfd1i&sig=KcS9lnSrBpleKfAYsaEKns528co&hl=de&sa=X&ei=IOVDU4-bBIjRsgbu64D4CQ&ved=0CDAQ6AEwAA#v=onepage&q=ISBN%200-7506-9%20166-2&f=false

ISBN 0-7506-9 166-2

because I dont know if the link works, and there are quite some books with the same title but different content.


So thats it, i hope someone will be interested in any of this.
Have a nice week.

[pgross]

Hmmm - lower resistor values will raise the current and saturate the opamp more.

The LM358 utilizes Class A/B output stages which are signal level dependable.

With smaller signal levels Class A stage is used, but as the signal level increases the opamp
will changeover to Class B - with a significant increase in crossover distortion as seen on the scope.

Just my 2 cents

/Peter

[Insoft]

In the video you terminated the opamp you were using, first time I here'd of it so would be interested in seeing a video of why one should terminate a opamp and what happens if one dosn't.

[Pilot3514]

Use torrent bro!

I did, hardly anyone used it.

IMHO, don't make it optional.  Provide the torrent file on you website and not the video file.  Those that want the video will use the torrent to get it.

You will always want to seed it to make sure it is always available, but you can control the bandwidth.

[David Hess]

PLEASE don't even suggest using opamps as comparators to newbies, or they might actually think it is okay and you know full well that it is not okay.

It seems ok for HP/Agilent/Keysight, this is from page 129 of the E3631A  schematic (a current product). U6 is an OP27 used as a comparator.

Pete

Operational amplifiers are often used as comparators because of their extra precision but an OP27 is one of the ones you have to be very careful about in this application because it has a very low differential input voltage range.  The input stage has back to back input protection diodes across the inputs to protect it from excessive voltages beyond which the base-emitter junctions will break down damaging them via beta degradation.  Your schematic does not show it but the input current is probably limited by resistance.

Decompensated operational amplifiers like the OP37 fair a little better in comparator applications because they are faster.

[Wim_L]

If a specific opamp can be used as a comparator depends on the opamp. They're not optimal, but some will work. Some others will malfunction (sometimes in destructive ways). Even if an opamp can be used as a comparator in some circuit, performance may be bad. Some opamps perform poorly when recovering from being driven into saturation (and they likely will be, if you're using them as comparators). They'll be slower than comparators too. Still, sometimes it's a reasonable thing to use an opamp as a comparator, if you've considered all the issues and made sure they won't be causing problems for your circuit. Here's a good overview:
http://www.analog.com/library/analogdialogue/archives/37-04/comparator.html

Likewise, a comparator might look like it could be used as an opamp, but comparators lack internal compensation (that's what makes them able to switch quickly). Trying to use them with negative feedback is going to cause oscillations. So that really isn't a good idea.

[David_AVD]

Finding comparators with push-pull outputs and more than 5.5V supply rating is surprisingly hard.  There are a couple that go to 16V, but that's about it.

[David Hess]

. . .
Use the right part for the job and stop thinking "short-cut", "good enough", etc. This is one of the reasons that there are so many cheesy, crappy products on the market today........Design Engineers cutting corners[/b]

Part of engineering is minimizing cost.

If an spare operational amplifier can be used to replace a dedicated comparator saving a package, why not?  I have also seen individual comparators like the LM339/LM393 externally compensated to perform the function of an operational amplifier.  An LM324/LM358 is better being an operational amplifier and an LM339/LM393 is better being a comparator but the least expensive solution may involve using one in place of the other.

One exception to the above that I have seen involves precision where a single slow but high precision operational amplifier replaces a comparator that would need a preamplifier anyway and speed is not an issue.

[EEVblog]

IMHO, don't make it optional.  Provide the torrent file on you website and not the video file.  Those that want the video will use the torrent to get it.

So I should ignore several thousand people who want the RSS feed and force them to either go without or use torrent?
I might as well stop the podcast version entirely and force people to download from youtube, that saves me a step and the hassle.

[Pilot3514]

IMHO, don't make it optional.  Provide the torrent file on you website and not the video file.  Those that want the video will use the torrent to get it.

So I should ignore several thousand people who want the RSS feed and force them to either go without or use torrent?
I might as well stop the podcast version entirely and force people to download from youtube, that saves me a step and the hassle.

I apologize.  I did not know that people where getting the videos via the RSS feed.  I watch them on YouTube from my mobile device.  Also, while that look forward to every video, have yet to listen to an Amp Hour.

[jucole]

Superb!