EEVblog

[@apino01]

I'm taking Advanced Analog Electronic Circuit Design at Johns Hopkins for a Master's and this video was EXACTLY what I needed to help me with my assignment. You're always so thorough and helpful, Dave. I really appreciate all of your videos and love that this video was on the money for me.

[@BelperFlyer]

I'm old enough to remember when 702 op amps cost a week's wages and suffered from 'purple plague' corrosion failure. Been retired a while but you videos stir up my old brain cells a treat. For the odd gain requirements the hardest thing is getting the right resistor values without resorting to pre-sat pots. Clear, concise and not too theoretical. For me no longer any practical use but it's good to know I haven't forgotten everything :)

[@emcgon]

I have missed Fundamentals Friday...its my favourite of the things that you do. This one was great...thanks.

[@PsiQ]

You wont believe how much i currently learn from your videos :-) Thanks for doing these !!

[@omegacsblog]

You mentioned the challenge of getting an E96 resistor set to handle the 3-stage form. I'm very analog-challenged, but if I'm reading things right you want a gain of 4.6414, so a resistor ratio of 3.6414. I have a Python script I wrote a while ago that trial-and-error's all the available resistor values, and it gets 1300 / 357, which is 0.0085% off across all 3 stages. 4-stage isn't as close, 1370 / 634 gives 0.176% off 100x. An interesting question would be what happens statistically with the tolerances of the 6+ resistors. I calculate worst-case with all resistors pegged the wrong direction for a 3-stage setup using 1% resistors at 6.15%, but what happens when you take the tolerance *binning* (bell curve) and run the math?

[@susceptibility_]

If you connect resistors series with the same tolerance, the resulting resistor will have the same tolerance as the individual ones. For example, 10 x 1kOhm 1% resistor in series makes an 10 kOhm 1% resistor. If each 1kOhm were in worst case 1.01 kOhm (1% error), then the sum of them would be 10.1 kOhm, which is still 1%.

[@gamccoy]

Great topic, Dave. I love these fundamental tutorials.

[@raguaviva]

Excellent video! Time to revisit an old project that didn't work just because I killed its gain by using a huge gain :) Thanks, and keep posting videos like this one!

[@RobertSzasz]

"All things being equal" always makes me think of spherical cows. Thanks for the great video.

[@eddyfontaineyoutu100]

Analog electronics, that the real thing !!!

[@tubical71]

Nice to be back in class, 1st row as usual;) Thanx Prof. D. Jones, great lesson!

[@scowell]

With a 2-stage setup, using inverting config allows easier resistor choices. Same for all even-numbered stage configs. Using even numbered stages as well as inverting config allows negative gain as well.

[@volodymyrzakolodyazhny]

Inverting config is easier only for second stage (third, etc). It isn't easy to implement inverting config in first stage, because of unsertain impedanse of previous part.

[@Kezat]

Love it Dave, great white board theory to practical demonstration transition, really tied it together.

[@magzire]

One smart guy, he knows his shizzle

[@Laogeodritt]

Adding more stages has diminishing returns as mentioned, and at some point actually reduces the total system bandwidth (eventually an extra stage does not add enough bandwidth to compensate the next stage's additional attenuation of higher frequencies). With that in mind I figured I'd make a few pencil scratches on the back of a napkin and figure out what the optimal number of stages is (yielding maximum bandwidth): n = 1/lg(2 lg A / (2 lg A - 1)) This yields a maximum bandwidth of: GBW (2 lg A / (2 lg A - 1))^(lg A) * sqrt(2 lg A / (2 lg A - 1) - 1) Given: - lg is the logarithm of base 2 - A is the desired system gain - GBW is the gain-bandwidth of the op-amps - It is assumed that each stage has the same gain and uses the same op-amp - It is assumed that BW is perfectly linear wrt effective gain Obviously, n must be a whole number, so round up/down, whichever gives the best result. Likewise, the maximum bandwidth formula is theoretical for a potentially real-valued n. This is rarely worth the effort in practice, I was just bored and don't feel like working on my Capstone project =P As Dave mentioned in the video, there is a diminishing returns effect---so in the video's example, 9 stages might give the best bandwidth (something like 170kHz effectively), but 8 stages only gives you 500Hz less bandwidth (not even 0.5% difference!), 7 stages costs you 2kHz or so (around 1%), and so on - those last few stages aren't worth the extra design and production cost!

[@tubical71]

At 15:30 you may add that: -3dB is as well as 45 degree phaseshift, as we all see clearly in your beautiful waveform display! Just to mention;)

[@suzesiviter6083]

Very useful thanks, I dont know how I have managed to miss this bit of theory in my careers.

[@jeremygrotte130]

I don't even bother waiting for the video to end before giving it a big 'Thumbs Up' anymore. They've all been great.

[@erikjohnson2976]

Great tutorial. Thanks, Dave!

[@weeeeehhhhh]

Fantastic stuff. Love fundamental fridays! Amy.chance you could add a tutorial Thursdays with more of this?

[@andreasroedwehage9135]

Brilliant video Dave.

[@666Pulsar666]

Glad to see you upgraded Dave CAD to gold version :D

[@RexxSchneider]

The only thing missing is the point that as we deal with larger signals, the slew rate can become the limiting factor, not the GBWP. For the TS912, with a supply voltage of 10V you can expect a slew rate as little as 0.8 V/μs, so for example, a 2Vrms (i.e. 5.6Vp-p) output will be limited to rather less than 100KHz, regardless of gain.

[@frankreiserm.s.8039]

You are easier to understand than my other EE teachers. Frank Frank Reiser Video/Audio Service

[@AttilaAsztalos]

Quite instructive and fun to watch - the minor quibble I have is that there's some mental gymnastics left unexplained: seasoned pros might not even understand what the difficulty is but it can really bog down someone trying to wrap their head around the math for the first time that the GBWP mentioned is not the frequency where you still _get_ your nominal unity gain (as some like me may have assumed) but the point at which you have _lost_ 3db of it (the source of the 0.7 figure). Yes, I know (now...) that that _is_ the definition of bandwidth, but the finer point that your theoretical "1MHz" setup is not expected at all to really do x10 at 100KHz but an actual x7 instead is not a straightforward one at all for someone just trying to follow the experiment...

[@Guatis2112]

Attila Asztalos t

[@herr_kukuffs]

Nice, Dave! Thank you! I think cascading OpApms could be really useful!

[@redtails]

3:07 well this is a good reason to use stereo or quad opamps, right?

[@t3du]

OK, Dave but which opamp will be the right one for this? the classic lm 741, tl 8082, or any with single power supply or dual? Its about choose the right one :\

[@EEVblog]

The right one for "what"? There is no application requirement here, it is simply showing that it's possible to do this.

[@MINUX75]

With ONE LM311 or any comparator and apply X100 directly, it's works very well and you have the bandwidth. No need to cascading Opamps. Bold cowboys do that.

[@vencibushy]

Dave, without realizing, you actually managed to link an economics law to electronics. That is the law of diminishing returns which states that in all productive processes, adding more of one factor of production, while holding all others constant, will at some point yield lower per-unit returns. How brilliant is that :)

[@Desmaad]

It's a fairly common term in engineering, if I understand correctly.

[@redtails]

Nice video! Very easily explained, even to non-ee people

[@sc0rpi0n0]

Thanks Dave! Just in time I need this.

[@HA7DN]

Dangit, I tought instantly about gain-bandwith product. I feel sooooo smart now!

[@GadgetUK164]

Excellent stuff!

[@georgevendras5450]

Very funny that @ 4:28 the zero in the denominator of the first ration (1 STAGE = 1MHz/100) moves a little bit to the right.

[@DavidLeeMenefee]

I like Op amps. Thumbs up Thanks

[@ernststavroblofeld1961]

ElectronicWizzard Electronics is like Lego for teenagers.

[@CNKayutube]

half a "bees dick" now that is funny i don't care who you are. lol You have some funny lingo down under. : )

[@christophers6034]

(.5 bee's dick) = .05mV ?

[@xDR1TeK]

Sex on a stick!!!

[@CNKayutube]

or OHHHHH burrbrown "it's almost pornographic"

[@rileystewart9165]

Not only did I learn how to do cascading op amp problems but I learned who Bobby Dazzler was LOL

[@ronaldlijs]

Good fundamental video, cheers!

[@elboa8]

Nice. Very clear. Keep them coming. Cheers.

[@redtails]

1:20 huh, thank you so much already, I always wondered about this

[@cronos51101]

Half a bee's dick, lol, I've never heard that one. OP amps are crazy man...

[@Electrotech1980]

Hi Dave, Thanks for the video. Can you please make a video on OP Amp compensation and why you can't cascade them in a single feedback loop? I did do that more than 40 years ago for a corrosion cell controller once. Not for bandwidth but for gain. I used a compensated amp and an uncompensated amp within the feedback loop to keep it from oscillating. Luc Boulard

[@reox42]

why do you write 2^(1/N)? You don't need the ^ symbol there ;) i always read that as "2 to the power of n times 1/N)" and wondered about the "n" :)

[@gregfeneis609]

Perhaps nuth n to worry about

[@foxyrollouts]

he must be used to using the keyboard, or hes trying to idiot proof it

[@TheDejfson]

What about the input offset when cascading.It was said that you have chosen this particular opamp because of the offset characteristics. Now if you cascade amplifiers, in worst case the offset maximum (peak, hence say 3 sigma) value could theoretically multiply by factor of four, which could result in an offset value exceeding an offset of another amplifier having probably larger bandwidth.right?

[@EEVblog]

It ain't that easy, it depends on the opamp topology and how the offsets are spread statistically (can be pos and neg). They could very well cancel out for example.

[@FireDragonAndromeda]

Informative as always.

[@Momonga-s7o]

Awesome channel, THANK YOU!

[@vsr600]

why didn't you use the HP spectrum analyzer for this? Seems like it would have been way more straight forward to get the frequency response....

[@GaziSharif]

Could some one please tell me the gain value is the feedback resistor value? Should I split the feedback resistor value in the case of cascaded op amps? For example, if I use 10 K ohm feedback resistor for one op amp, in case of two cascaded op amps are these 100 ohm each?

[@alijafary5559]

is it ok to cascade multiple mfb band pass filter to achieve more bandwidth?

[@uccoskun]

dear Dave: What are the small "n" and the big "N" in your formula?

[@vigsgb]

Why increase the bandwidth? Will it give quicker reaponse times on the measurement or increase what can be measured?

[@douggale5962]

I love how the bandwidth formula gives 0 for N=0, if you ignore the destruction of the universe in the exponent. The universe wouldn't have exploded if it used negative exponent notation.

[@BrentBlueAllen]

"Half a bees dick"!? Even more-so than the EE knowledge you've shared, I appreciate the Australian slang.

[@tonnyodekerken9013]

Oh 2014. Do you still read the reactions? Can you explain when you (not ‘you’ but in general) use V_dB versus P_dB. Clarify: you say in the beginning GBPB=-3dB bandwidth. You point at an opamp that has infinite input impedance and nothing is connected to the output. Should it then be 6dB? No power gain. I know the ‘3dB’ is carved in our brains. But theoretically?

[@Nordic_Mechanic]

When did you upgrade your daveCAD license to gold?

[@obiwanjacobi]

Excellent! Thanx!

[@00Skyfox]

I'm still confused. What exactly is meant by "bandwidth" in terms of opamps?

[@NinjaAdorable]

+00Skyfox The frequenzy over which the opamp will provide use-able gain. ie upto -3dB gain can be tolerated. So the frequency range which goes from 0dB to -3dB will make up the op-amp's BW.

[@antonioferraoneto6681]

Hi Dave, do you have some reference book about this subject?

[@coder1016]

Thanks man!

[@yaghiyahbrenner8902]

good video. why didn't you frequency compensate your stages, this could have improved the design better ?

[@EEVblog]

This isn't a "design", it's a quick check to show that the bandwidth does increase in line with the theory.

[@yaghiyahbrenner8902]

:) yeah I feel you. would be good to start looking at this some time in the future as part of the op-amp series really great set of videos. I see you updated to the Dave Cad "Gold Edition" I was told its only limited to 30 nodes. :D

[@gabriellgardin]

THANK YOU !!!!

[@electronic971]

great video and explication !! merci pour toute c'est vidéo :) But i have question : what if my different stage(OPs amplifier ) haven't the same GAIN.....

[@eiler89]

Hi Dave! I love these practical design theory videos =) But one question, how do you know that the OpAmps both come from the same die?

[@EEVblog]

Because there is only one die inside the chip containing both opamps.

[@eiler89]

EEVblog Ah, of course! I thought I saw two chips there :p

[@PhN1800]

Great video! :)

[@ManofCulture]

SO can i use series of OP amps to increase my internet bandwidth :D

[@andrefbos]

Isn't noise a high frequency signal? If so, doesn't it get attenuated by the limited bandwidth of the op amp?

[@peterpv0001]

Nope, but it depends on the type of noise. 1/f noise for example has more power at lower frequencies. Thermal noise is flat over frequency. But you're right that high frequency noise is attenuated by the bandwidth of the system but so is your input signal so you gain nothing.

[@williamhazelwood8288]

Uncompensated Op amps are all i have.. made me cry :(

[@redtails]

7:24 well.. I don't see much point going above 3 stages.. Unless you're looking at gains of tens of thousands to millions, it's not going to do much

[@DrEnginerd1]

Do butterworth next

[@yevhenzabila320]

Thanks for this video, it's very helpful for the beginners like me. I built my amplifier based on two Non-Inverting OPA694, about 2 x 20dB=40dB voltage gain. I need both DC and AC amplification, i.e. full bandwidth from DC to 100MHz is required. Is anybody suggest how to modify cascade in order to get rid of an offset?

[@joblessalex]

Nice! Would it be cheaper to just buy an op amp with 10-20 mhz gbwp?

[@EEVblog]

I explained that. There are situations when you are forced to use this technique. You can't just buy a better opamp.

[@joblessalex]

EEVblog Once again jumped the gun and posted before I got there.

[@ratbag359]

very helpful knowledge :)

[@frankm.9356]

Dave, at 04:10, you define "BW" as the bandwidth of a single stage. Using this definition, the formula probably should be BW_TOT = BW^N * Sqrt[2^(1/N)-1] i.e. "BW^N" instead of "BW". I found another formula here: demonstrations.wolfram.com/SystemBandwidthForCascadedAmplifiers/ (The formula is: Sqrt[BW^2/N], which results in 70.7kHz for two stages of 100kHz). Now I am wondering which is of two formulas is correct.

[@frankm.9356]

Sorry, I was wrong with "BW^N"; "BW" is correct.

[@27merk]

Dave, if you have time just a 2 min supplementary vid on the differences between cascading two (or 3) different BWP & Gain amps. Just curious that's all. ps stop castrating those bees!

[@IanGrall]

And right when I thought I was going to bed..

[@dankennedy2491]

So in theory running your op amps at higher voltages can increase your GBWP?

[@peterpv0001]

Depending on the opAmp, yes. Not all opamps have a GBWP that is dependant on the supply voltage. And in practice you're of course limited by the maximum supply voltage that the opAmp can handle.

[@EEVblog]

No, not all opamp are like that. You also have slew rate limitations at high output voltages. Your GBWP may not hold at full output swing. I guess I forgot to mention that...

[@yoghurtwow]

lovely , really.

[@pocoapoco2]

actually 12k and 3.3k will get you spot on to 4.6416 if you choose a 12k that's a tiny bit high and a 3.3k that's a tiny bit low.

[@stargazer7644]

What part number do I use on digikey for "12k that's a tiny bit high"?

[@pocoapoco2]

@@stargazer7644 kzbin.info/www/bejne/Z4ikmYeajKqlqLc

[@alperenalperen2458]

I am curious about the calculation of bandwidth in such case. Could someone give me a refrence?

[@alperenalperen2458]

shomolya could you try this one plus.google.com/u/0/107666507827268479667/posts/Mv1C1DJSWQE?pid=6204062777226647122&oid=107666507827268479667

[@alperenalperen2458]

+shomolya I liked your way to appraoch the problem. what you do is basically(correct me if I'm wrong) you obtain the transfer function of the filter in terms of power(not voltage) and set it to 0.5 right? Btw we should really be having this conversation in the EEVBlog forum. :D

[@antonioferraoneto6681]

Does anyone know any reference on this subject?

[@mitchellscales8846]

didnt know adafruit is selling your uCurrent

[@edocodIT]

"The chip isn't cheap" "The chip isn't cheap" "The chip isn't cheap" "The chip isn't cheap" Is it just me, or this sentence sounds funny? :P

[@MarcinKurczalski]

DaveCAD upgraded to GOLD? xD

[@Etude888]

One could download the free TI TINA Simulator to verify the principles here.

[@Alex-cj7ro]

same is on ur t shirt

[@lakshminarayanaaithal1081]

I guess the distortion is due to the low skew rate of TS912.

[@VoyuerHole]

lol. Half a bee's dick...I don't remember that being in the SI system! : )

[@maksym2k]

You're way too young to know all of this. Admit you know how to time travel.

[@AnatoFIN]

Maybe speek bit slower and make video longer pls

[@darer13]

no

[@weeeeehhhhh]

Fantastic stuff. Love fundamental fridays! Amy.chance you could add a tutorial Thursdays with more of this?