Cant oscillate sine wave from "bubba" oscillator

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Hey,
Mt project is DC/AC inverter.
In this project i am using a "bubba" ocsillator as a sine ref circuit.
Whan i am tring to simuliting this ocsillator using "Pspice" i get a DC wave at the outputs.
whan i have wireup'd this circuit in reality i have succssfully saw the sine wave.
why i cant see sine wave in Pspice?

thanks!
Liran

An oscillator needs a tiny signal to amplify and feed back. In a real circuit, this is started with noise and transients. In pspice, there is no noise so some oscillators never start.

It appears your simulation is set up improperly. Look at the schematic you supplied of the configuration you say works. Note the gain of the only non-follower amplifier and the DC voltage on the non-inverting input of same. With that gain, the 0.5V would supply ~2.6V for the signal reference for all stages of the single-ended supply used for the oscillator.

Now look at your sim's equivalence. What will happen when the amp tries to amplify that 6V input with that gain. Take a look now at the divider R7/R8. The sim might yield a result if the reference voltage is corrected; I didn't look further.

So u meen that this sophisticated progrem cant simulate such a simple oscilator?

mneary said:

An oscillator needs a tiny signal to amplify and feed back. In a real circuit, this is started with noise and transients. In pspice, there is no noise so some oscillators never start.

Click to expand...

There is no option to determine noise in pspice?
thank you,

Liran.

It is too bad that Pspice does not know that the LM348 quad opamp you selected is one of the oldest and noisiest with very poor spec's.

LFU said:

There is no option to determine noise in pspice?

Click to expand...

Pspice includes noise in the AC noise analysis mode. It does not include it in transient analysis. To get an oscillator to oscillate in Pspice, you may need to inject a small transient into the circuit at the start of the simulation. This can be done by using a voltage-controlled-voltage-source inserted at an appropriate spot in the oscillator and injecting a small single pulse. Such a source appears as a short after the signal is injected so it will have no effect on the rest of the simulation.