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- Опубліковано 15 вер 2014
- Op amp gain-BW product and slew rate limiting are defined, discussed and demonstrated on the bench. This discussion applies to the majority of general purpose op amps on the market - as most op amps are internally compensated with a single dominant pole. High speed op amps, unconditionally stable op amps, non-unity gain stable op amps, high power opamps, etc. may not follow these characteristics because they are often compensated differently in their design. An LM358N is used for the example circuit. Other popular op amps like the LM741, etc. will behave in a similar way. Sometimes the slew rate limit of a device will be the dominant factor in determining the bandwidth, and other times the gain-bandwidth product will determine the resulting frequency response. The video demonstrates why this happens. Notes from the video are here:
www.qsl.net/w/w2aew//youtube/o... - Наука та технологія
Really great explanation! I hadn't looked at slew-rate limited signals on the scope like that -- very good way of showing the problem.
Applied Science Thanks Ben - much appreciated!
I'm finding your channel the best of all of the EE blogs. Dave and signal path are ok but the waffle on to much about smeg, you are straight to the point in an entertaining way
Good way in skewing the problem 👍 nice video and good information!
The way you explained slew rate was the best I've ever heard or read anywhere. Great job!
Very good demonstration. I have read slew rate in datasheet often but understood it really with this demonstration and explanation. I like the attenuation box you use.
That all makes a lot of sense. You can tell a great teacher, it seems obvious as they explain things.
Thank you so much for working on publishing this video. You have marvelously explained the difference between operational amplifiers gain BW limit and slew rate. Hats off.
Brilliant explanation as usual. Thank you.
A tear fell when you pulled out the datasheet "book". Excellent.
Excellent descriptions as always. Thanks for taking the time to put this together.
Excellent information and demonstration thank you! I've been having refresh/learn things about op-amps lately for our senior project and this video helped very much!
Awesome practical demo! I really appreciate the balance between theory and real-life measurements.
Please keep doing. You have found the optimal way to merge theory and practice. I have studied these "boring " things over 20 years ago. Now they are exiting thanks your videos.
the demonstration of the slew rate limiting the frequency response of the opamp was so sweet!!!! I have not done the connection between slew rate and freq response.
A very, very well done, easy to understand explanation. Link to video instantly forwarded to my hobby network.
Excellent! You laid out in 15 minuets what it took for me; three months of college study to understand back in 1986, with some help from Walter Jung, of course. Alan, you did an outstanding job! Thanks for your hard work.You make it look so easy however, I'm well aware that it takes a lot of hard work, not only for the concept and math, circuit design and build but the mere production of these videos. Thank you so very much for your hard work to make electronics so easy for saps like me...!
Excellent!!! It is interesting how the slew rate of the op amp is not affected by the frequency of the signal but basically by the amplitude of the signal.
Thanks Alan. It's always a pleasure learning from your videos.
Exceptional explanation. Precise and compact, thank you very much!!
Very well composed video. You are the best in explaining the basic things.
Brilliant video. Suddenly I understand why my home brew function generator acts wired at higher frequencies.
Thanks a lot.
This is absolutely brilliant. Very well explained. Now I can sleep on class and learn at home!
Many many thanks to you, I'm designing a 2-switch forward converter, and need to do with op-amp feedback compensation. This video make me recall things on my electronics class. :) :)
Thanks! Studying op-amps right now for class and this was confusing me. You made it very clear!
Cool! Be sure to tell your fellow students about my channel, and even your professors! Where are you attending school?
Wow that is such a great class! Thank you for sharing such knowledge!
Just watched like 10 of your videos, great stuff!
Thank you so much for the explanation of the slew rate, helped me a lot!
your videos are helpful as they are more practical and hands on..thanks for it
Nice explanation about slew rate!!! Very helpful!
Very good explanation....Learned the concept practically..just amazing
Stellar video. Thank you so much for the great lesson & demo.
Thank you,I never understood slew rate until now.
Best explanation of slew rate and GBP
Great description of GBP. I am jealous of that old databook as well it looks like a great book. Thanks for the vid
I used to have an entire library of the old databooks and applications books from the major semiconductor manufacturers. They were (and still are) a tremendous resource of information. Over the years, my collection is whittled down to just a dozen or two...
@@w2aewyou lent them to other people and never saw them back? 😅
@@keylanoslokj1806 Many of them stayed at the companies that I worked for.
Really helpful explanation. Can you make a video on opamp stability and capacitive loading ? It really helps the way you explain it with actual demo. thanks again.
Really great explaination and to the point ,you are inspiration to many
awesome job explaining. Super helpful, thanks
That is my dream oscilloscope. I regret not buying it when i bought an expensive one. I have the tds2002c which i use more haha.
That scope is how old now and still holds its value and has a floppy drive. Tektronix are the best. Im restoring one for a friend. Hes had it in storage for a few decades so im not even sure what the model is. If i knew i could get that scope id sell almost all my gear. I tend to donate my gear when i get new gear. The tek diff probes are so expensive. Id trade my rigol mso5354 and every other piece of gear for that scope and a nice selection of probes. There's a reason you work for them but havent replaced the 3104.
Great video, thanks. Ive found that i had to buy caps that are above my budget to get most opamp circuits to look as perfect as yours.
Sorry for rambling i have severe ptsd. I shall get my ham license in the new year.
Super clear . Thank you for doing this video. Liked and subscribed
Very helpful video, everything is described in a very calm and demystifying manner.
Btw: whats the purpose of the 2.2k resistor at the Output?
John Matrix The output stage of the LM358 uses a push-pull output stage that has some crossover distortion. Using a 2.2k resistor to ground keeps the stage in the "push" mode (sourcing current) so that I don't incur the crossover issue. Also, the spec sheet for the part specifies the output characteristics with a 2k load, so I figured I'd come close to matching that.
***** thanks for the quick response, now i get it. since i´m a electronics newbie i`m not yet into checking datasheets before asking questions :-)
Interesting info. Will be fun to repeat this experiment
An Exceptional Narration!
Awesome tutorial. Thank you!
Even though you teach "negative feedback", I am sure no one can ever give you a "negative feedback". Thanks a lot sir. Clear. Compact. Beautiful.
Thank you. I do get negative feedback sometimes. There always seem to be a few thumbs down on my videos...
w2aew they hate you cause they ain't you 😂😂 We love you sir 😊
Fantastic video and all in 15:30 minuts !
Thanks for such quality tutorial!
отличное видео. Спасибо. Как мне не хватало таких видео лет 30 назад :)
That's easy for you to say.
Your explanations are the best!
Thanks again, Alan. Great vid.
Thank you for your efforts. This is an excellent video.
This is great stuff, I just came across phase reversal on a LF353 working as a voltage follower when reaching Gnd. Luckily I also bought TLC272 that did that job perfectly single supply. I know it was a rookie mistake but what better way to learn.
Yes, some op amps have that unexpected phase reversal when you violate the input voltage range. Very nasty, and lock up a system. And, often not specified in a data sheet!
This is briliant explanation. Thank you.
Fantastic as always, thanks.
Great as always! Thank you!
Thank you for the nice video. Great stuff
Excellent explanation!
Thank you Alan. Superb....
Really as always. Great teacher
Great work man,keep up
As usual, another excellent and lucid video.
I was wondering why you used attenuator and didn't just change the singal amplitude from the FG.
Thanx for the great video.
I wanted an amplitude (under the high gain case) that was below the minimum output level of the generator.
Thank you for the video and clear explanation i have learned soemthing new today.
Very informative, thanks!
I was thinking, if you put two common emmiter transistor amps on the output of the opamp and take feedback from the collector resistor of the second transistor back to the opamp feedback resistor network, would that somehow enhance slew rate or/and the gBW product?
thanks a lot from the depth of my heart
this a classroom should be thank you sir !
Nice refreshing content!
Good video!
Thanks a lot, exelent video, keep up the good work :-)
Thanks for this awesome video
It seems to me, that in most applications we wouldn't want to be slew rate limited. That is, we would want to hit the 3dB corner (f_3dB), or the full power BW, before we hit the slew rate frequency (f_SR). We can check if this is the case from the op-amp's data sheet, which gives us its GBP (gain-bw-product) and its SR (slew-rate).
We have: GBP = (A_CL)(f_3dB) or f_3dB = GBP/A_CL. We also have SR = 2(pi)(Vout_pk)(f_SR) , or f_SR = SR/((2pi)(Vo_pk)). Using Vo_pk = (Vin_pk)(A_CL) this last equation can be written as f_SR = SR/((2pi)(Vin_pk)(A_CL)). So we need f_SR > f_3dB, or SR/((2pi)(Vin_pk)(A_CL)) > GBP/A_CL, or SR/((2pi)(Vin_pk)) > GBP.
If this isn't true then our application needs an op-amp with a larger SR and or a smaller GBP (or we need a redesign where we start with a smaller input signal Vin_pk). Am I thinking about this correctly? Thanks!! And beautiful job on teaching about closed loop f_3dB and SR !!.
Thanks so much for your videos
Great video, thanks a lot.
This was really helpful
Is there any difference in gain bandwidth product between inverting amp and non-inverting amp while calculating V out ?
I mean I watched a video regarding GBP and teller said
Fu = Acl x Fcl in Non-invering amp
Fu= ( |Acl |+ 1 ) x Fcl in inverting opamp
Does it make sense ?
This was extremely concise and well paced and informative. Thanks so much for your videos!
I had a few questions about the caps in your test circuit. I'm assuming the 0.1uF cap going from your divider reference to ground is a bypass cap to limit noise from the op amp, right?
As for the 220uF coupling cap, was there any reasoning in picking that value or is it what you had on hand? Additionally, would this cap and the input impedance of the op amp form a high-pass filter? It seems like the 3db point would be nearly 0?
I'm still learning the fundamentals and trying to piece together all these EE ideas in an intuitive way. Your videos have helped immensely in that quest.
Thanks again
Yes, cap values aren't critical. The 0.1uF is to keep the noise down at the non-inverting input. The 220uF is what I had laying on the bench, and was large enough to be "invisible" at the lowest frequency I intended to test with (~1kHz).
Thank for share, very usefull for me, for make good preamp
Regards,
hello Sir, could you please suggest me what type of op amp can I used to amplified small sine wave signal with frequency range of: 17MHz to 27MHz?
Depends on the amount of gain you need, as well as output voltage swing, available supply voltages, load impedance, etc.
As usual, so clear to make me understand at first time! Are IC switching power regulators in your "to do" list?
Max Petrus That's another that's been on my list for a long time. Just haven't had the hours it takes to put something together on that yet.
I wish i could vote it up a few more times so that Mr.Alan Wolke does it sooner :).
Thanks very much.
I’ve been trying to find a single step attenuator like wavetek you have in the video but unable to find anywhere. Can you recommend any alternative to the wavetek ? . I’d love to run these tests as well
Lots of manufacturers make them, but aren't cheap!
www.jfwindustries.com/product-category/manually-variable-attenuators/50-ohm-dual-rotor-attenuators/
www.apitech.com/products/rf-solutions/passive-coaxial-products/manual-step/9000-series-manual-step-attenuators/
www.pasternack.com/50db-step-sma-female-sma-female-2-watts-attenuator-pe7398-p.aspx
thumbs up before I watched it - for the topic
So if I want to have an useful gain for for example 27 MHz so I need like an ultra fast Op Amp right? Like 1 Ghz at least ?
Yes - which is one reason why you don't often see op amps being used at RF
great explanation thank you :-) u r very good!!
Very nice! thanks :)
How didi u select the value of resistors and capacitors
Nothing special. I wanted two equal values to setup a 50:50 voltage divider for the non-inverting input. I have a big pile of 3.9k resistors, so I used two of them. For the gain setting resistors, I chose values that are simple "in your head" calculations.
thank you very much
Excellent video. Few questions though. How did you come up with all the 220uF (reverse polarity here I think), 470 and 0.1 uF ? Aren't the 220 and 470 too big ? Would some bulk decoupling like 10uF instead of 470uF work ? Thanks.
Nothing critical. 470uF for good bulk supply filtering, value not critical. 220uF for input coupling, just a large value laying on the bench that would provide a low impedance a the low-frequency end of the testing, and 0.1uF for decent medium/high frequency decoupling of noise at the non-inverting input. In all cases, values could vary quite a bit with no change. Just handy values found on the mess of a bench...
Thank you.
what is purpose to use 470uf cap on non inverting line.
Filter for the +5V power supply. Really has nothing to do with the function the non-inverting line.
A fascinating demonstration.
Regarding the phase delay introduced when the slew rate limit is reached: is this a constant? You pointed out that the falling edge has a slightly different slope than the leading edge and this was clearly seen. Two thoughts on this. (1) is this predictable enough that it has utility in a design? and (2) as a phase delay appears to be present (although you didn't show the waveform just out of the signal generator), is this useful in certain applications - and perhaps undesirable in others?
k1mgy I didn't show the phase delay, but there certainly is a delay encountered as you near the GBP limit, and a further delay as you hit the slew rate limit. It would be unwise to use this in a design because the performance, particularly slew rate, may not be well controlled between devices, and will vary depending on operating conditions. Not shown was that the asymmetry of the rising and falling slew rate limit is also dependent on the input common mode voltage.
Why did you stop increasing the frequency when the voltage dropped to 700mV?
Because that is the -3dB point, which is where the bandwidth is traditionally defined.
Brilliant!!
Awesome! thank you
wow this mean mostly all opamp distort square waves .. what do you recommend for perfect square waves amplification?
It all depends on how fast the rising and falling edges of the square wave has to be. This directly relates to the required BW needed by the amplifier.
need to be really fast and no overshoot from 20hz to 20khz .... also need to be very low noise, most of opamp i've seen have overshoot in the datasheet.. ringing on the attack.. or are very slow in term of slew rate.. also do you consider well made open loop to be better than close loop for SQ.. lets say you could EQ digitally first
why do you use a sine wave for your test hehe.. should be an ultra fast pulse made by ultra fast pulse gen..
do you like AD8009 or AD844
also for SQ.. how important is voltage noise density versus current noise density
also what is the importance of quiescent current..
one of the best square wav i can find is from LM6172
Hey Alan,
Thanks for uploading another great video!
I hate to be picky, but I noticed something in your diagram of slew-rate-limiting at 10:20.
You drew the slew-rate limited waveform being in-phase with the the input signal (or a non-slew-rate-limited output signal).
However, shouldn't the slew-rate-limited signal lag the input signal by some phase?
The drawing wasn't intended to show input vs output, but rather just comparing normal vs. slew rate limited output waveform shapes. If it was showing input vs. output, then yes there would be a phase shift.
At minute 3:38 the formula for BW is very similar to the formula for calculating the scope BW based on the signal rise time. The diff is in the 0.35 constant. Are they really related?
Yes - it's the same single-pole rolloff relationship.
Brilliant video. What opamp should I use to amplify a 1mhz audio signal by 20db?
Can you clarify? 1mHz is 1 millihertz, or 1MHz is 1 megaherts - neither of these are audio signals.
@@w2aew Mega. Your right. It is for ultrasound. I am having trouble moving from all these theoretical videos to moving to a practical two stage amplifier at 20db per stage.
@@fernandohood5542 20dB gain at 1MHz means that the op amp would have to have more than 100MHz unity gain BW - that is a tall order! You may have to use several cascaded stages with lower gain in each stage, in order to get the gain you want at 1MHz.
hey, i was wondering if you have a vector network analyzer in your lab?
Unfortunately, no, I don't.
***** Hi, A great home built VNA is the N2PK VNA. The VNWA is also good. N2PK: n2pk.com/ Up to 60MHz, I built it for around $350.00. VNWA: groups.yahoo.com/neo/groups/VNWA/info Up to 1.3GHz +
I wouldn't be without my N2PK VNA. They are a great learning tool.
Thank You!
Excellent.
As always a great video! :)
can u tell me plz how u calculate 707mv....
Bandwidth is defined as the half-power point. Remember that power is equal to voltage_squared divided by the resistance.
Thus, dividing power by 2 is equal to dividing the voltage by sqrt(2). 1/sqrt(2) = 0.7071
Great Video. I did not know that 2 different aspects effect the BW of the opamp. I used to believe that slew rate was the only cause of the band width limitation.Thanks to you video the concept is very clear.
Any reason for using the Attenuator. Can the experiment be done by varying amplitude in the signal generator controls ?
Mainly because my signal generator output control didn't have the range I wanted - plus the attenuator gives the advantage of maintaining the generator's SNR for small signals (since the attenuator reduces the signal and the noise equally).
Oh ok. Thank you :)