Colpitts Oscillator Circuit Analysis (7 - Oscillators)
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- Опубліковано 6 жов 2024
- Let's design a radio frequency Colpitts Oscillator together. We'll be using a common-emitter configuration bipolar transistor.
Aaron Danner is a professor in the Department of Electrical and Computer Engineering at the National University of Singapore.
danner.group
Video filmed and edited by Cheryl Lim.
@randomcheryl
I am an aerospace engineer and a very beginner Electronics Amateur. You videos are the best I have found so far.
My only wish is that you keep up with the good job!
Thanks
This video is incredibly good. And the same can be said about the rest of your videos. The way you develop a topic is just perfect. I am very happy I came across your chanel, and I hope many will find it.
This is by far the best L-C oscillator analysis I've seen on You Tube.
The only thing I would do different is to add a section to emphasize the physics of the resonator tank circuit and the transformer like qualities of C1 - C2 and L in the resonator network i.e. A=-C1/C2 (gain required).
look at 5:23 the guy said this using impedances X1 and X2
I am new to electrical engineering and find this presentation helpful. Thank you for making the complex understandable.
Brilliantly clear. Thanks again. Hope your channel grows exponentially, you have a gift for explaining things.
Very good explanation. Only one note: the circuit at time 5:49 is not an common emitter because of the presence of RG
Aaron, your videos are great!!
Your contents deserve many more subscribers!!
Thank you very much!!
Excellent presentation. Learning my things again in a new way.
Hello professor Danner,
You made very complicated subject look so easy. Thank you.
Can you create another lecture that relates to a common base oscillator? Please include mathematical derivations where others rarely do. This is very interesting because common base has wider frequency range. Or I am wrong about this?
Nice video, hope you could made a practical design for high frequencies.
Hello, can you explain the example of a metal detector with search coil head? great explanation
I get a lot of FM activity in my research of making a DIY transistor amp.
Thank you for your clear presentation. I am a little confused however about why the development of the conditions of oscillation are dependent on the existence of Rout. If the amplifier was perfect, Rin would be infinite like you assumed and Rout would be zero. Without the Rout term X1+X2+X3 would not need to be zero so you couldn’t derive the frequency equation or the gain relationship.
I understand that in the real world amplifiers have output impedances but is there a way to derive the relationship that ignores this fact?
Charlie
In this oscillator, it is required that there be a non-zero Rout (or that there be some kind of resistor there). If the amplifier were perfect and Rout=0, then Z2 would have no effect on the voltage at node V2 because Z2 would be in parallel with a perfect voltage source. There would then be insufficient phase shift around the loop to achieve oscillation; the equations would thus fail to give a single frequency of oscillation without the added constraint as you rightly pointed out.
@@adanner Thank you. I did do a calculation along the lines of V2/V1=Z2/(Z2+Z3), V1/V2=Z1/(Z1+Z3) …. Multiply these together, set them to one and you get the required Z1+Z2+Z3=1 relationship. I think this mimics the situation if Rout=0. It is all academic I suppose since we do live in the real world without perfect amplification. I was thinking of the impedance element as a filter so I approached it as such.
I very much appreciate your presentation. So often I see a superficial approach like calling the impedance in this oscillator a tank circuit when it really isn’t. Yes the equation is the same for the frequency but no one but you showed mathematically the inverting nature or the feedback decency on Z1 and Z2.
Once again, thank you. Charlie
@@stevekim6923 Yes, it is equivalent to what is written since (X1 + X3) = -X2.
@@adanner Thank you very much! Before you answered this, I deleted the question because I understood it later on. I guess i wasn't fast enough.
You could look at his two port network examples to see why you don't want a voltage source driving a capacitor. infinite current required?
Why is ((V2/V1)(V1/V2)) = 1 is needed?
I need the thoery behind this equation... All the analysis is very clear.. But
At 3:28
You just jumped to derivation by saying my " strategy is just to multply this two term... " and am lost there🙏🏾🙏🏾🙏🏾
I'm still a little unclear on the function of the capacitor, Ce
RE is used for BJT DC polarization (and designed to get a gain of 1 at DC or low frequencies), but for AC this resistor may be too high and CE allows to lower emitter resistor (and increase BJT gain at high frequencies to make sure the oscillator keeps working) by connecting RG in parallel to RE.
RE has function to keep polarization stable avoiding HFE variations cause by temperature changes or transistor substitution with different HFE's. CE desacopplishs RE avoiding change DC polarization and increase considerably the gain of amplifier because the AC signal won't see RE and it will can use the DDP RE to increase his excursion over VCE. The amplifier gain without CE will be RC/RE, but whit CE the gain increase a lot and to don't distort the AC signal he put a serie resitor that work like RE just to control the excursion of the AC signal without distortion.
Make a video on how to profit with that information next
Other than the feedback network, is there anything else we need to alter in order to achieve higher frequencies?
How does the LC tank provide the extra 180 degrees of phase shift required? I've tried AC analysis, but I could only find an extra 90 degrees
Hi Aaron, thank you for this series of videos. I have one question regarding the equivalent circuit used to derive the conditions of oscillations, i can see that you used the Op. Amp equivalent circuit for the amplifier, is there a reason to use this model instead of the hybrid model or the pi model?
Students sometimes find the abstract models too difficult at the beginning, so I'm trying to avoid them and instead concentrate on the oscillation condition.
Could a 14Mhz colpitts oscillator be feasible on a breadboard with every other rail removed to reduce the parasitics?
What’s the use of colpitts oscillator
Hello profressor, I am a Bsc student in computer engineering, and currently writing my thesis and I want to reference this video in my paper. I have a question. At 2:05, when you first apply the voltage division method to find V1/V2, you do not take into account Z2 in the denumerator. But later on, when you give V2/V1, you treat it like a parallel impedance (which is logical). I tried solving the same way you did but I used Z2 as a parallel element in the V1/V2 equation as well, but I got 0=1 as a result, so I assume my logic is flawed somewhere, and yours is correct. Can you please explain why you did it like this?
Finally I have figured it out. Yes, V2 is in fact dependent on Z2 through the fact that the current in the branch depends on it, but it does not matter, since we have to multiply with both the numerator and denumerator with this current and so it cancels out.
This also applies in the V2/V1 case, but the current is the generator current, and it also cancels out. I wrote this answer to my own question in case someone else needs it in the future. :)
What is the type of transistor used BC107 or BCC547. Please reply.
Why don't inductors delay current?
Hello Prof Aaron!
At 4:00 Why do you neglect Rin if the impedance in the base of a transistor is high? Isn't Rin supposed to represent the input impedance of the transistor?
There is a resistor in serie to CE to control amplifier gain. This resistance is reflected to the base multiply to HFE. This way if the resistor value is 500 Ohms and HFE 100. The resistance seen from the base will be 50K Ohms plus rpi which depending Ib current.
Thus Rin will be in fact much bigger than Z1 and the equivalent resistence will change just a little bit.
Could you please tell me why did you use the strategy to multiply v1/v2 by v2/v1 and assigning 1 as a result. This condition is related to Barkhausen criteria.
When considered X1+X2+X3=0 was to guarantee phase zero? Another condition from Barkhausen?
@@MrCleitonls correct
Thanks 😁
Noice.