Episode 1769 What is cascode and why do I want one Opto Cascode: • #798 Optocoupler Optoi... W2AEW: • #207: Basics of a Casc... Be a Patron: / imsaiguy
😊 Very good explanation. I noticed that at 13:28, referring to the 2nd transistor, you said Common Collector transistor: actually it is a Common Base. Anyway, waiting for part 2 to complete the lesson...regards from Italy.
Although I already knew about and have tested a BJT-based cascode and knew about the Miller effect, this explanation really cleared up some points for me. A really simple and clever circuit!
Cascode drives in the way you showed here were used (because of the benefits you mentioned) as video amplifiers in old CRT TV-s and monitors. Also, one interesting feature, since the lower device is working with colector (or drane) voltage being arbitrary defined via biasing the upper device, cascodes were also used in industrial offline flyback power supplies, working from input voltage in the range of 200-1000V. They would use some really high voltage bjt (and a slow one also) and drive its emitter via some light, low voltage and low Qgate mosfet. Ofc, these solutions are now obsolete since one can buy SiC, GaN and other "exotic" semiconductor devices (mainly mosfets) working with around a 1.2kV of a drane voltage and also having really small Qgate and Rdson. :)
Had to dig out this circuit recently as I needed a MOSFET to handle 3kV in linear mode. Those SiC and GaN devices are for switching only and not rated for linear use, so I had to stick to ancient planar MOSFETs.
@@inse001 I'll find you a few publications I had back in the day about that, and I'll be glad to send 'em to you, though they tackle the problem of a cascode in a switch mode regime. But, I see no problem in making as many (must say theoretically) staged cascode as your power supply voltage dictates. If You use for example 3 NHL160N120SC1 mosfets, 1200V, 160mohm, 34nC gate charge devices. Bias the second and the third one at 1000 and 2000V respectively, and make the lowest one (the one at the 0V) an op-amp controlled current sink. Ofc, you'll have to take all the percautions of RF and HV designs since SiC are damn fast components and 3kV is really unforgiving voltage level...
@@ivanpopovic9503 Thank you very much for the offer. The problem is already solved, I cascoded four BUZ50A (1000V) to form a constant current circuit sinking 1mA from 100 to 3000V to keep an electrophoresis power supply activated. It monitors the output and switches off in case no load is present. I found support in The Art of Electronics and the EEVBLOG forums.
When I was a teenager, our tv died and the tech changed a high voltage driver transistor BU208A. This transistor had a 750V Vce and 1500V Vbe with the gain of 2! I always wondered why such a stupid low gain transistor needed to drive the high voltage.
If my memory does not fail me, a gentleman at Tektronix, by name Gilbert, introduced cascade use for beam deflection in the ever faster oscilloscopes. Two of my (employer’s)early oscilloscopes were rated 450 and 500 kHz. A Solartron scope around the same time was as fast as 5 MHz. Then I found a plug-in module for the old 450 kHz scope, boosting it to 20 MHz. Also, if anybody built Heathkits, there was a 5 MHz scope kit offered. Then came (and stayed for a while) the “standard” 100 MHz rated scopes, thanks Mr. Gilbert.
Thanks, very nice explanation of how they work. I have seen them used in older receivers but never really thought much about how they worked. Makes perfect sense. I will have to play with them once I get my lab set up again after getting new flooring installed. I need to take a trip over to Anchor, haven't been there in months. Craig
Very well explained. Cascode amplifiers are good when a higher frequency response is needed, and you can even add more cascode stages. With a single cascode stage, it is the same as a common base stage. Several years ago I listened to a UBC EE prof give a talk on a company's laser diode driver chip. It used an emitter couple pair with current sources as an output stage. The UBC prof referred to it as a cascode. He was not happy when I corrected him. I don't know if he had designed the custom chip, but I found several problems with it. I had been hired to give an independent evaluation of it.
Cascode can improve frequency response by factors of 50 or more. In this case the 5.1 k resistance between the amplifiers is limiting the effectiveness; an inductance to block the AC through this path will greatly improve the frequency response. (Or use separate dividers for base bias...)
Im finding things strange (but really cool) lately because every video i look at has something i need in a few projects im doing.. Like just now before I clicked this video i was thinking of amplifiers.. The universe is been good to me..😊👍🇮🇪
The miller capacitance is only in inverting amplifiers. The AC voltage across the capacitor is the (voltage gain+1) times the input voltage and efffectively shunts the input to ground at higher frequencies.The effect increases with the amplifier stage gain.
You are an excellent teacher - explained briefly and effectively! The cascode effect with the dual gate Mosfets was hidden from me until now. Are there also Cascode amplifiers with 3 transistors or can the effect no longer be improved? 73 de DL1LAJ, Andreas
On a BJT datasheet, look for "transition frequency," which is typically denoted f_T (f subscript T). Also, look for the gain-bandwidth product on other amplification circuits. That should get you pointed in the right direction 😉
The name "cascode" was coined in an article written by Frederick Vinton Hunt and Roger Wayne Hickman in 1939, in a discussion on the application of voltage stabilizers.[3] They proposed a cascade of two triodes (the first one with a common cathode setup, the second one with a common grid) as a replacement for a pentode, and so the name may be assumed to be an abbreviation of "casc(aded triode amplifier having characteristics similar to, but less noisy than, a single pent)ode".[4] Cascode circuits were employed in early television sets for the 'front-end' or tuner because of their low noise and wider bandwidth.
Thank you. I found a nice explanation on the Analog Devices wiki. In a nutshell "The base [...] of the cascode device is electrically AC grounded, so charge and discharge of stray capacitance [...] between collector and base [...] is simply through RL (the output load) , and the frequency response is affected only for frequencies above the associated RC time constant" - which would be a pretty small RC and hence a high frequency.
Thank you for the shout-out to my video. I agree - our videos often complement each other very well.
😊 Very good explanation. I noticed that at 13:28, referring to the 2nd transistor, you said Common Collector transistor: actually it is a Common Base. Anyway, waiting for part 2 to complete the lesson...regards from Italy.
Although I already knew about and have tested a BJT-based cascode and knew about the Miller effect, this explanation really cleared up some points for me. A really simple and clever circuit!
As always, your videos are a treasure. Thank you.
Cascode drives in the way you showed here were used (because of the benefits you mentioned) as video amplifiers in old CRT TV-s and monitors. Also, one interesting feature, since the lower device is working with colector (or drane) voltage being arbitrary defined via biasing the upper device, cascodes were also used in industrial offline flyback power supplies, working from input voltage in the range of 200-1000V. They would use some really high voltage bjt (and a slow one also) and drive its emitter via some light, low voltage and low Qgate mosfet. Ofc, these solutions are now obsolete since one can buy SiC, GaN and other "exotic" semiconductor devices (mainly mosfets) working with around a 1.2kV of a drane voltage and also having really small Qgate and Rdson. :)
Had to dig out this circuit recently as I needed a MOSFET to handle 3kV in linear mode.
Those SiC and GaN devices are for switching only and not rated for linear use, so I had to stick to ancient planar MOSFETs.
@@inse001 I'll find you a few publications I had back in the day about that, and I'll be glad to send 'em to you, though they tackle the problem of a cascode in a switch mode regime.
But, I see no problem in making as many (must say theoretically) staged cascode as your power supply voltage dictates. If You use for example 3
NHL160N120SC1 mosfets, 1200V, 160mohm, 34nC gate charge devices. Bias the second and the third one at 1000 and 2000V respectively, and make the lowest one (the one at the 0V) an op-amp controlled current sink. Ofc, you'll have to take all the percautions of RF and HV designs since SiC are damn fast components and 3kV is really unforgiving voltage level...
@@ivanpopovic9503 Thank you very much for the offer.
The problem is already solved, I cascoded four BUZ50A (1000V) to form a constant current circuit sinking 1mA from 100 to 3000V to keep an electrophoresis power supply activated.
It monitors the output and switches off in case no load is present.
I found support in The Art of Electronics and the EEVBLOG forums.
Very interesting .. thank you 👍
When I was a teenager, our tv died and the tech changed a high voltage driver transistor BU208A. This transistor had a 750V Vce and 1500V Vbe with the gain of 2! I always wondered why such a stupid low gain transistor needed to drive the high voltage.
Vote more circuits , less old measure stuff..
Good content , canot wait part 2.
BOTH is great! :)
YES! thanks.The "miller killer".
Also an Early killer 😉
That begs a cascode chip of the day video: MC1110, CA3028, uA703, and 3N35 NPN Tetrode.
If my memory does not fail me, a gentleman at Tektronix, by name Gilbert, introduced cascade use for beam deflection in the ever faster oscilloscopes. Two of my (employer’s)early oscilloscopes were rated 450 and 500 kHz. A Solartron scope around the same time was as fast as 5 MHz. Then I found a plug-in module for the old 450 kHz scope, boosting it to 20 MHz. Also, if anybody built Heathkits, there was a 5 MHz scope kit offered. Then came (and stayed for a while) the “standard” 100 MHz rated scopes, thanks Mr. Gilbert.
I know cascode circuits with tubes, still a nice explanation.
Thanks, very nice explanation of how they work. I have seen them used in older receivers but never really thought much about how they worked. Makes perfect sense. I will have to play with them once I get my lab set up again after getting new flooring installed. I need to take a trip over to Anchor, haven't been there in months.
Craig
Very well explained. Cascode amplifiers are good when a higher frequency response is needed, and you can even add more cascode stages. With a single cascode stage, it is the same as a common base stage. Several years ago I listened to a UBC EE prof give a talk on a company's laser diode driver chip. It used an emitter couple pair with current sources as an output stage. The UBC prof referred to it as a cascode. He was not happy when I corrected him. I don't know if he had designed the custom chip, but I found several problems with it. I had been hired to give an independent evaluation of it.
Excellent, thank you. Actually you explained 5 principles in a very effective way.
Cascode can improve frequency response by factors of 50 or more. In this case the 5.1 k resistance between the amplifiers is limiting the effectiveness; an inductance to block the AC through this path will greatly improve the frequency response. (Or use separate dividers for base bias...)
Brilliant video. I must breadboard this out. You are a great teacher.
I learned something new
Thank you very much for the lesson! Why I love physics, you can study it forever!
Im finding things strange (but really cool) lately because every video i look at has something i need in a few projects im doing..
Like just now before I clicked this video i was thinking of amplifiers..
The universe is been good to me..😊👍🇮🇪
Good stuf Mark I viewd the W2AEW video when it was first published. I'm going back to view it again
Awesome thank you..........cheers.
The miller capacitance is only in inverting amplifiers. The AC voltage across the capacitor is the
(voltage gain+1) times the input voltage and efffectively shunts the input to ground at higher frequencies.The effect increases with the amplifier stage gain.
Cool video
Two 2N2369s would be pretty quick in this circuit, not in a breadboard though!
We need less Emitter Bitter, on the whole Wiggle Wiggle.
4:07 😋
Wiggle, wiggle, wiggle
Just a little bittle
...
You are an excellent teacher - explained briefly and effectively! The cascode effect with the dual gate Mosfets was hidden from me until now. Are there also Cascode amplifiers with 3 transistors or can the effect no longer be improved? 73 de DL1LAJ, Andreas
three doesn't help
How does a dual gate FET compare to a tetrode (dual grid thermionic tube/valve)?
When selecting transistors, what datasheet parameters do you look for to ensure higher bandwidth circuit?
On a BJT datasheet, look for "transition frequency," which is typically denoted f_T (f subscript T).
Also, look for the gain-bandwidth product on other amplification circuits. That should get you pointed in the right direction 😉
The amplifier came from tubes. I believe it meant Cascaded Triodes.
The name "cascode" was coined in an article written by Frederick Vinton Hunt and Roger Wayne Hickman in 1939, in a discussion on the application of voltage stabilizers.[3] They proposed a cascade of two triodes (the first one with a common cathode setup, the second one with a common grid) as a replacement for a pentode, and so the name may be assumed to be an abbreviation of "casc(aded triode amplifier having characteristics similar to, but less noisy than, a single pent)ode".[4] Cascode circuits were employed in early television sets for the 'front-end' or tuner because of their low noise and wider bandwidth.
Thanks for posting. Question were you an educational instructor at one time?
no
@@IMSAIGuy Ok. I was just wondering. I like your teaching style.
How does a double gate FET compare to a tetrode (double grid thermionic tube/valve)?
Do the FET versions rely on a similar Miller capacitance effect to make it happen in that topology? I'm guessing so.
Yup
Yes.
The input wiggle shouldn't be more than 10 mV.
I admit I must be missing something, but why doesn't the Miller capacitance of the top transistor now become the villain?
you need to study common base amplifiers, they have no miller effect.
Thank you. I found a nice explanation on the Analog Devices wiki. In a nutshell "The base [...] of the cascode device is electrically AC grounded, so charge and discharge of stray capacitance [...] between collector and base [...] is simply through RL (the output load) , and the frequency response is affected only for frequencies above the associated RC time constant" - which would be a pretty small RC and hence a high frequency.
@@thelastofthemartians if you want more: th-cam.com/video/tAK8Q5IZjng/w-d-xo.htmlsi=yxtKcfJt7jr8FvuE