RC Phase Shift Oscillator (using Op-Amp) Explained
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- Опубліковано 24 сер 2024
- In this video, the RC phase shift oscillator has been explained and the expression of the frequency for this RC phase shift oscillator has been derived.
By watching this video, you will learn the following topics:
0:29 How RC Phase Shift Oscillator Works
1:45 Simple RC Circuit (Phase Lead Circuit)
5:35 Design of RC Shift Oscillator using Op-amp
7:31 Derivation of the frequency for the RC Phase Shift Oscillator
RC Phase Shift Oscillator:
In this oscillator, the RC network is used in the feedback to generate the stable sine wave. This oscillator is the harmonic oscillator (As it generates the sine wave)
RC Phase shift oscillator is used for low-frequency generation (Up to few Hundred of kHz). Typically it is used for the audio frequencies.
In RC Phase Shift Oscillator, the transistor or op-amp in inverting mode is used for the amplification. So, it provides the 180 degrees of phase shift. And the remaining 180 degrees of phase shift is provided by the RC feedback network.
By tuning the gain of the RC network and the amplifier it is possible to achieve the unity loop gain.
In the feedback loop, more than two RC stages are cascaded to achieve the stable phase shift.
If three stages are used for then the attenuation provided by the feedback circuit β= 1/29.
And the frequency of the oscillation f = 1/(2πRC√6)
In general of N stages of the RC circuit are cascaded then
f =1/(2πRC√2N)
In the RC phase shift oscillator, usually the R is kept fixed and C is changed to tune the oscillator. And for proper tuning, all capacitors are ganged together.
This video will be helpful to all the students of science and engineering in understanding the RC Phase Shift Oscillator.
#RCPhaseShiftOscillator
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The timestamps for the different topics covered in the video:
0:29 How RC Phase Shift Oscillator Works
1:45 Simple RC Circuit (Phase Lead Circuit)
5:35 Design of RC Shift Oscillator using Op-amp
7:31 Derivation of the frequency for the RC Phase Shift Oscillator
Besten Dank für dieses Video
Many thanks for this video
from Switzerland
Took me a day because there was no equation number given but it was helpful!!! Thank you
I'm here to just say "Thanks" for sharing awesome knowledge in this 17 minute video.
Good explanation and approach to the results.
The math is kind of long but i simulated the circuit using LTspice and plotted the ratio of Vout/Vin and it came out to -1/29th as in the video. Thank you. You are so good with the math you should go back for your doctorate.
Did you simulate the rc network and it vout/vin or including the opamp?
Great that you know to use spice
Please educate me a bit about that when you have time
@@abhijithanilkumar4959 do it yourself lazy man.
What is spice
@@deitybasumatary7497 A kind of biryani
Your derivation was so much better, my lecturer Laplace transformed the circuit and ended up getting 3x3 matrix and the derivation was worth over 5 pages
Thank you so much for such video! May the Lord Jesus bless you.
Super sir easy to understand... thank you
Please upload a video on RC phase oscillator using BJT
Yes please do
kudos from india
sir I love the way you explain the topics. please make a video on phase locked loop.
watching before attempting my 4th try in the exam!
Thank u so much for this.
Man, you are my hero
Thank you for detailed explanation sir
Very good video. You have made a good video which can be referred for technical exams.
thanks a lot, taught me more about circuit analysis!
Hi, all about electronics. I just see one error on the diagram: R1 is virtually connected in parallel to R, affecting the gain calculation. Instead, R is in feedback to the input without R1.
Thank you. Very helpful.
your intro is best sir,,,we feel chilled whenever we open any video.....
thanks for this type of kindness😊😊
Excelente vídeo, tudo parece tão fácil. Saudações do Brasil
It helped me a lot sir
Loved it👍
Thank you so much
शानदार explanation... Hartley oscillator भी krao
Very good explanation
Very helpful👌
Thnqq 4 the video...it's really helpful
Why is it assumed that the entire current I3 flows through R and is not split into 2 currents, one flowing through the resistor and one flowing out to the right of the circuit? When the RC circuit is connected to the amplifier circuit then there will be a current flowing in at Vin and a current flowing out at Vout, so why is only the current flowing in at Vin applied during the derivation?
Also thought about that
The only reason to recharge my phone is to watch NESO academy and ALL ABOUT ELECTRONICS.
AOE is the real khalnayak
@@abhijithanilkumar4959 What AOE?
@@rishabhpathak1367 All About Electronics
sajan re jhooth mat bolo khuda ke paas jana hai
very cool, you nerd..
بارك الله فيك وهداك
excellent explanation sir
thank u
Here,
Phase shift per attenuator is 60.
so, tan(60)=sqrt(3)=Xc/R
==> Xc=sqrt(3)*R
So, Vin/Vo=1-j*sqrt(3)
And we also know angular frequency , w=1/(j(Vin/Vo-1)*RC)
So, in this case angular frequency , w=1/(sqrt(3)*RC) Not your mentioned : w=1/(sqrt(6)*RC)
Note: I can be wrong, but I found this from my calculation. thanks at all for great video.
Great stuff! You always have clear explanations
How about some videos on:
In rush current, FETs, LVDS, Voltage doubler, buck, boost, buck-boost, and flybacks?
super ur videos with clean nd good information nd explanantion🤗🤗
Very nice explaination sir 👍👍👍👏👍👏👏
Thank you sir
Thanks a lot.great explanation
absolutely love your derivations
Great! Note - you say "into" when you mean "times"
You are الأفضل يلا... استمر يلا... يا هندي...
This may be a stupid question, but if you change R and C in the RC ladder do you change the gain from 1/29 to another value?
THANK so much you Sir .
Great sir
Really nice video :)
thank you so much
Sir the equivalent ckt you draw the output is first taken from opam directly and in second ckt output is taken after the phase shift ckt .will it produce the same output.
very good
I don't understand op amp holds up to 18(VCC) and 18(-VCC)
We need A= 29 ' any help
Gain is ratio between output and input voltage, not the value of output voltage. Let say you input is 0.1V and your output is 2.9V, so 2.9/0.1 = 29 (Gain)
It is great .THANK YOU.
Hi, how this circuit is in positive feed back? as per my understanding oscillator must be in positive feed back? but this circuit seems to be in negative feed back?
Try to understand in terms of the loop gain of the circuit. For oscillation, AB should be slightly more than 1 right. And around the loop, the phase shift should be either 0 or multiple of 2*pi.
Here the RC feedback circuit attenuates the output signal by the factor 1/29 at the oscillation frequency. And it also introduces the 180 degrees of phase shift between the output of the op-amp and the feedback signal which is again given as input.
On the other end, the op-amp provides the gain of slightly more than 29 and as it is connected in the inverting configuration, it also introduces the 180 degrees of phase shift.
So, overall loop gain becomes slightly more than 1 and the phase shift around the circuit becomes zero.
In short, it satisfies the conditions required for the sustained oscillations.
I hope it will clear your doubt.
Connecting to the negative (inverting) terminal doesn't necessarily signifies that the OPAMP is in negative feedback. Notice that the gain of feedback loop is -1/29, which is itself negative. Hence negative feedback with negative gain (attenuation in this case) cancels each other and the overall feedback is positive.
What will be the amplitude of the output sine wave??.....calculation can be made easy by using transfer functions but this is the easiest way to understand....thank you
I think this depends on the op-amp, since this is an oscillator you would have to check the slew rate for the maximum frequency and the rail voltages for the sine wave amplitude.
Thanks sir🔥
Thanks
Thanks a lot bro.......... 01 June 2024 ko mera viva hai😅....
many many thanks to ALL ABOUT CIRCUIT for express the RC-phase shift oscilator easy and nice way
That one south asian guy on UA-cam
Nah, it's called Indian!
@@aryanprakharsame difference
Your name is Aaryan Upadhyaya, you're a South Asian guy on UA-cam too
@9:45 why we are not applying KCL at Vo? in this case it is open but what about when we connect it in the feedback path?
Great job
Its exactly awesome
Super sir...
Why using 0 - tan inverse eqn for the phase shift?
Is there a short way or a formula for calculating the attenuation factor(beta)? It will be pretty time consuming to solve such big equations during examinations.
Very good
Awesome!
Superior
Thankyou sir
Why we only change the value of capacitor to get a desired frequency ¬ change the resistor value
Sir, since we are giving the feedback to the negative terminal, will it not become negative feedback? please help me out...
It will be considered as the negative feedback if the phase shift of the output waveform is zero. But if the phase shift of the output becomes 180 degree ( -vout) then it will become positive feedback. J hope it will clear your doubt.
@@ALLABOUTELECTRONICS thank you sir...i understood it👍👍
Just great...thanks
Rushal Bhai..!!Will you please make a video about bootstrapping technique in emitter follower amplifier????
Yes, When I make a videos on transistors, I will cover it.
i loved it
It would be nice if you provide in the end of you each video a simulation, ex in proteus, of your circuit. So we do know what is really going on. My onpinion.
Ive watched all your videos for Opamp and you are just amazing ,
here I got a small doubt in 1:19 time of this video you said vout is in 180 phase shift but our input and feedback both are at + i.e non inverting then how come our vout is inverted ?
What I mean to say is, the feedback circuit ( RC Circuit) provides 180 degree phase shift to the incoming signal (output of the opamp) at particular frequency. Therefore at the oscillation frequency, ideally the output of the opamp ( which is input to the feedback circuit) and feedback signal ( output of the RC network) will be 180 degree phase shifted.
Of course, the overall phase shift of the circuit is 360 degree, and that's what we required for oscillation.
I hope it will clear your doubt.
Hi all about electronics. I have just a minor question on 6:34. I am just confused because here the op amp has a negative feedback. Isn't negative feedback used when we want our op amp to function as amplifier and positive feedback if we want to use it as oscillator?
Since this is an RC Phase Shift Oscillator, shouldn't we use positive feedback in it?
thanks sir
The circuit diagram shown at 5:37 has Vout at terminal of Rf,while redrawn circuit diagram have Vout at terminal of R1 !.How can it be correct? Please clarify my doubt...
thanks in advance.
Yes. It's by mistake. It has to be on the left side.
Anyway thanks for pointing it out.
Thankyou...
In 14:28, why will the output voltage only have a real part?
it's a trick to find frequency
For the angle of feedback circuit to be 180 degree... Imaginary part should be zero.. Then only tan^(-1)(y/x) may be equal to zero... Subject to condition that real part of beta must be negative...
Hello, can we use voltage divider method?
Can anyone tell me how the formula for phase shift came at 2:36
How it can acts as a positive feedback?
Sir, why can’t we use cascaded low pass filters instead of high pass filters?
why can't we do it like this?
V1=Vin*R/(R-jXc)
So similarly, Vo=Vin*R^3/(R-jXc)^3
by this way w=1/rt(3)*R*C
which is coming wrong, please answer it is urgent, i have exam tomorrow.
at the ending, you called Vo/Vin the attenuation, I though it was the gain and attenuation was the inverse?
Isnt there a minus is absent in equation of Xc? Zc = jXc = 1/jwC = -j/wC -> Xc= -1/wC ? I am very confused because of it I could not drive the same formulas with you
How can you measure that Attenuation ?
Hello , have you samthing about open and closed loop gain?
Super sir
sir pls write the point which u explain so that it take less time to make notes during watching the lecture
Hi, I need to design a rc phase shift oscillator for 150hz can you please help me selecting the values..
Can you explain why you said that gain will be 0 in two cascaded RC circuit when R=0? I am finding the gain to be 1.
When 'R' is equal to zero, the ground resistors are not present. Therefore, the feedback circuit contains a bunch of capacitors in series with the feedback resistors. This causes the gain of the feedback loop to plummet.
It's not true that in case of cascading all the three will be having same phase shift !! Right.
14:24 , can you elaborate on why the output voltage will have real part only , and can we cascade it with low pass filter and if we can , will there be any change in the result?
In oscillator, although in the input (the thermal noise) there are many frequencies, eventually we are getting the output oscillation only at the specific frequency. So, we can say that there is a sort of resonance at the specific frequency. And in resonance, the input and output are in phase. Therefore, the imaginary part will be zero.
But why this phase shift due to rc is not introduced in wein bridge oscillator
I know it may sound dumb
But is noise sinisoidal
Or how the the variation in DC current is sinusoidal
And it's amplified and given back
So if it's not sinusoidal how we got sine wave???
Thanks
The noise does not contain single frequency. If it contains a single frequency then it is easy to identify or eliminate that from any system. But if we talk about the noise, Its combination of all the frequency.
So, when it is amplified by the amplifier, all the frequencies in the noise signal gets amplified.
But the feedback network acts as a frequency selective network, which passes only certain band of frequencies and attenuates remaining frequency. So, over the time only single frequency is able to get amplified and all other frequencies gets diminished.
When we say a single frequency in the frequency spectra, in time domain, its a sinusoidal signal of that frequency.
So, with proper gain tuning, we are able to get a sinusoidal signal of a single frequency.
I hope it will clear your doubt.
@@ALLABOUTELECTRONICS got it sir
Thanks
@@ALLABOUTELECTRONICS oh
Is it like A. Beta less than 1 for the other frequencies thus they Eventually damp and die out??!
@@abhijithanilkumar4959 Yes, exactly.
At 5:41 In the figure You getting Vout From the RC feedback output I don't understand this point because generally we get the Vout from output of Op-amp.
Here this Vout is the output of the RC network. So, what I mean is, the output of the RC network is given as an input to the op-amp. Of course, as you said, the overall output of the oscillator circuit is the output of the op-amp. If I have used the different nomenclature for the two outputs (the op-amp and the RC network output) then this confusion would not have arised. But I hope, you got the point. If you still have any doubt then let me know here.
@@ALLABOUTELECTRONICS so My exam starting this month for revision I watched so many of your videos that I am used to your voice because of this I am reading your reply in your voice in my mind..
Good
Sir actually l don't like the electronics... After seeing your video I understood, about the electronics now I began to love it
so in this cas, depending on how much RC curcit is cascaded to each other the formula of "f" will change. and since f changed the attenation factor won't be equal to 1/29. right? so we will have to change the gain of opamp. right?
Not only the gain, but you also need the look at the phase. You also need phase of 180 degree, so that the overall phase is 360 degree.
Sir why 60 deg each nw equally ,is possible to three diff cimbination to achieve 180?