Electrical – Phase Shift Oscillator not Oscillating

oscillator

May I please ask why my phase shift oscillator as shown is not oscillating?
My R1=R2=R3, and C1=C2=C3.
I am trying to get around 1kHz of oscillation, so using the simple equation of fr=1/(2*piRC*sqrt(6)), I get all the values as shown in the pictures.

But why is it not oscillating?
I tried at both Multisim and LTSpice, but it just doesn't simulate.
I am using ideal opamp at both simulators (gain is very high, 200x let say).
I put Rf(feedback resistor of opamp) to be 220k to have Rf>29*R, which will make the loop gain >1 (to fulfill the Berkhausen criteria), but it is still not oscillating. I thought the circuit fulfills both of the criterion for oscillating to happen?

I tried changing Rf to even higher value, and even play with the RC values. I also tried to use LM741 op amp and rise the supply voltage slowly, but I never get oscillation.
May someone please give me enlightenment on what is wrong/lacking?
Thank you very much.

phase shift oscillator

Best Answer

For some oscillators, it helps to "kick-start" to get them going in a simulation that doesn't model the noise that gets a real oscillator going. In this case, the kick-start is done by initializing node n005 to 0.01V (anything other than zero volts). Node 5 is at the right-hand end of C3:
A phase shift op-amp oscillator

This oscillator uses a virtual op-amp with open-loop gain of 100K. Since it has no power supply and is perfectly linear, oscillations grow exponentially...forever.

XU1 N001 0 N002 opamp Aol=100K GBW=10Meg
R1 N002 N001 180k
R2 0 N003 560
R3 0 N004 560
R4 0 N005 560
C1 N003 N002 .1µ
C2 N004 N003 .1µ
C3 N005 N004 .1µ
R5 N001 N005 5.6k
.IC V(n005)=.01
.tran 0 .1 0 .00001
.lib opamp.sub
.backanno
.end

Your oscillator also hasn't quite enough phase shift.

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