BJT Circuit Analysis: The CASCODE Amplifier (Pt 1) (066g1)
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- Опубліковано 8 лип 2024
- Here is yet another configuration of bipolar junction transistors called the CASCODE Amplifier.
It has its roots in the 1930s and was originally created with triode vacuum tubes to extend the high-end frequency response of video amplifiers.
This is the introductory video explaining the WHY behind this configuration and the HOW it works behind its operation.
In the next video I wil be showing you how to design one and demonstrating the benefits of this configuration both in the simulation world and with a bench experiment.
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Time Markers for Your Convenience
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00:05 Initial Comments and Introductions
01:26 Device Capacitances
03:42 What is the Miller Effect?
05:35 The CASCODE Amplifier's Architecture
06:42 How does it work?
09:03 Parting Comments and Toodle-Oots
Excellent video. Thank you very much. I look forward to the follow-up one. God bless!
Thanks, man! 🙂
Thanks for making this video, the great thing about UA-cam is that you can re-watch until you have learnt and understood everything taught.
True that! And I've done that many times. Also, I've provided time markers in the description if you need to jump to a specific place. just click on the marker and you are there. 🙂
@@eie_for_you Time markers are a great help, thank-you!👍
@@acestudioscouk-Ace-G0ACE You are very welcome! 🙂
Very nice video and explanation.
Your narration is also astoundingly clear in the way how you emphasize the important passages and such.
Very well done!
Thank you so very much! I really appreciate the encouragement! 🙂
Great tutorial Ralph. Thankyou
Thank you and you are very welcome! 🙂
This circuit was commonly used for the RF amplifyer in TV tuners connecting to the antenna and valves were used.
I would that there is a LOT less inter-element capacitance with a vacuum tube. Thus the higher frequency capability. 🙂
Perfect! Thanks for sharing and take care.
You are very welcome, my friend! 🙂
Once again, this was exceptional. Thank you Ralph for all your excellent teachings. 73
You are very welcome! 🙂
Damn Ralph, I'm 61 and today is the first time I finally figured out that my brain is like an ice cream cone. No matter how many times you melt it, I can always pull another out of the freezer... Thank you for doing that thang that you do.
You are very welcome, my friend! 🙂
BTW, i always do the thumbs up before I watch the video, but i often forget to do it with your fine vids. Like devouring a fine steak and someone asking if i want steaksouse... Too busy doing Num Num Num....
Now that is a very interesting analogy! Thank you for the encouragement! 🙂
👍Thank you sir.
You are very welcome! 🙂
I think I might have to watch this 2 or 3 times before it sinks in.
I know the feeling! There are some things in electronics that take a bit of work to understand what is going on. 🙂
Note for new players:
The names of the capacitances vary depending on what school you went to. There isn't really a standard naming in that form.
I use Ceb and Ccb as the names.
It is also easier to type.
Also:
If you put a resistor in series with Ce (on his design) to lower gain, it is also good to change where Cb hooks.
Basically you put the resistor on the ground end of Ce and run Cb to that spot also.
This gives you a higher input impedance.
Actually, the gain of the common emitter amplifier, Rc/Re, might be significantly less than 1. Cascode also greatly reduces the Early effect.
But, in its interaction with the common-base, it does approximate a gain of 1, in practice. This is how it was explained to us in engineering school and in the texts I reviewed to create this video. 🙂
@@eie_for_you With no emitter degeneration resistance, Rc=re for the top resistor and Re=re for the bottom resistor. In this case, the voltage gain is very close to 1, but the combined gain is not well-defined and varies greatly with signal level. Assuming gain=2 does consider the worst case for the Miller effect and is therefore not a bad strategy even when using emitter degeneration resistance to stabilize the gain..
@@byronwatkins2565 I hear ya! 🙂
INTREGUING!I HOPE I DO NOT GET LOST WITH THE DESIGHN EQUATIONS.AT ABOUT WHAT FREQUENCY DOES THE MILLER CAPACITANCE BECOME A PROBLEM?
Well, the frequency limitations depend entirely on the specific transistor being used. It also depends on the gain you set it up for. You can control the overall gain by splitting the emitter resistor, the bottom one is bypassed. The top one works together with the collector resistor to set the overall gain. The lower the set gain, the broader the frequency response. All of this will be covered in the next video where I go through the design and then we will see the results of the design including the "limited gain" version. 🙂
Audio.
@@andymouse Actually ... the main purpose was to extend the frequency response out far enough to be used as video amplifiers. This puts it well up into the MHz range. But, the actual extent depends entirely on the specific transistor you are using and the amount of actual gain you design into the amplifier. 🙂
It is going to also depend on your signal source's impedance. Remember that "Miller capacitance" is the gain of the stage times the Collector-base capacitance. This capacitor works against you signal source's resistance in
F=1/(2*pi*R*C)
If you make a stage with a gain of 100 using a transistor with a 1pF collector to base, you get 101pF seen at the input from that.
If your signal has a 200K impedance, the result will be good enough for voice but not hifi.