yashgumaste

modified 10 years ago

Working RC phase shift oscillator

133

01:33:33

Thank-you @hurz for helping. ☺
RC phase shift oscillator

Theoretically, The gain of Feedback circuit is 1/29.
So I adjusted the gain of Amplifier to 29 for sustained oscillations. Rf=29*R1
But I increased the gain a bit to 44.7 by
Rf=29Kohm
R1=649ohm

To get frequency of 1Khz
F=1/(2×π×R×C×√6)
Assuming C=0.1uF
R=649ohm

published 10 years ago

WTFCircuit

10 years ago

I think you have to kickstart the circuit giving it a scake

hurz

10 years ago

1. Gain has to be a little more then 29 e.g 29.1 ; 2. You forgot the input impedance of your inverting opamp circuit. Increase both resistor or calc the last phase shift resistor new with the given 1k one in parallel ; homwork ;-). 3. Go down in sim speed to 100us/s. 4. Even if its oscillating, its not a nice sine wave because of clipping. 5. Set back opamp gain to default, otherwise you cant do the math to calc approx 29.1 gain. Hope this helps.

yashgumaste

10 years ago

@hurz removing the last rc phase shift resistor, does the trick. See there, I added a switch. Will this work on breadboard?

hurz

10 years ago

You didn't get the point. Why not replace 1k with 649 ? And all other tipps i gave?

yashgumaste

10 years ago

@hurz ok done, so we have increased the gain to 44.7 i didn't understand why does damp at high simulation speed. Will it work on breadboard ?

hurz

10 years ago

Why 44.7?

hurz

10 years ago

Define what happens gain < 29 < gain only for sn infinite small part! And for the case of exact 29! Three different situation. This kind of oscillator i would call labile

hurz

10 years ago

Yes, its working inreality as it runs here in simulation. Only difference, in simulation you have numerical loss by interpolation and more important by undersampling.

yashgumaste

10 years ago

Its the gain if Amplifier = Rf/R1 = 29K/649 = 44.68412943 ~44.7

hurz

10 years ago

From filter seen now, there are 2 resistors 649Ohm to ground. One can be removed. The one for the amp is needed.

yashgumaste

10 years ago

Yes I removed the last 649ohm resistor. Is it correct?

hurz

10 years ago

Yes, impedance is now ok. But frequency is still wrong and will never be exact what this formular give you. Cuz this kind of osci must go into clipping and this shifts the out spectrum partly into higher regions. All in all amplitude and phase get distorted and the hole thing is nonlinear. How bad is that?... But this can be reduced by using as close as possible the perfect gain value with some little +. Your gain now is by far to high with 44.7

yashgumaste

10 years ago

So let R1 be 1Kohm. But still freq is not matching theoretical value

hurz

10 years ago

I try again :-( your rc shift circuit is made by 3x times r and c. The third R is the input resistor at opamp. The neg input can be seen as grounded!!!!!!!!! Think about.

yashgumaste

10 years ago

I didn't understand. I am a beginner. Please explain in simple language. Can you build it for me.

hurz

10 years ago

If you are a beginner start with "examples".

hurz

10 years ago

BTW, i already made a circuit you probably haven't seen. http://everycircuit.com/circuit/6249235795148800

add comment in editor