Twin T Oscillator

157

03:46:33

Can anyone tell me why the twin T oscillator is supposed to oscillate? As I see it here, the op amp is set up as a comparator and an integrator. 

I see the noninverting input as the bias point, meaning, that if the + input is higher voltage than the inverting input, the output will be high. So, here, unless the button is pushed down the inputs are equal, as the output puts out a voltage equal to the + input.

But, I cannot see what causes this circuit to oscillate (as it does in real life). Any hints?

published 10 years ago

antilogues

10 years ago

PS Happy new year!

Secuture

10 years ago

95% feedback rc or rl oscilators works by means of positive feedback obtained by delaying or advancing feedback signal phase and also serve signal shaping. this is achieved by those all phase shifters as this twin t filter u have here. frequency is then at such magnitude on whose phase shift is equal 180 degrees so it changes from negative into positive feedback. if amplifier can have a direct curent positive feedback as opamp then feedback serve only as signal shaper changing normally achieved square wave into sine as in "lo-pass hi-pass loop" oscillator for example (notice that transistor alone is not capable of such positive DC feedback exept few models that allow device to amplify curents without help from other device means have HFB alpha exceeding unity value)

antilogues

10 years ago

Hmm. I understand what you are saying in general. However, in the circuit here, I've used a feedback loop, and still the output of the op amp does not oscillate between high and low.

jman

10 years ago

I Think As With Op Amp Relaxation Oscillators U NEED Some Positive Feedback From THE Output To THE + PIN. Usually a resistor from the output to + then a resistor from + to gnd

jason9

9 years ago

What you need to do is set the upper potentiometer to 83% or more. You also need to set the time scale to 1mS/S in order for you to be able to see the oscillation. The lower potentiometer will control voltage.

add comment in editor

EveryCircuit is an easy to use, highly interactive circuit simulator and schematic capture tool. Real-time circuit simulation, interactivity, and dynamic visualization make it a must have application for professionals and academia. EveryCircuit user community has collaboratively created the largest searchable library of circuit designs. EveryCircuit app runs online in popular browsers and on mobile phones and tablets, enabling you to capture design ideas and learn electronics on the go.