Sine Waves from OP AMP Help

[johnsold]

I tried searching your college website for courses/engr332/Handouts/oscillators.pdf. It found the course but all it had was a short description. I suspect that you have to log in as a student or instructor to access the heandout.  Or at least I need the ... part of the URL.

Try putting the .pdf in a zip file. You can attach those.

Lynn

Edit: I found it by searching for the TI number.

[johnsold]

I put together a simulation of the Wien Bridge Oscillator in Figure 8 of the SLOA060 document.  I used a T074 op amp because I had a Spice model of that device.   I also changed to a +/-15 V power supply and grounded the point marked 0.833 V in Figure 8.

When I ran a transient simulation all signal voltages were constant within microvolts of ground.  This is not unusual in oscilator circuits because the only noise in the "circuit" is due to numerical round off in the simulation and it is often too small to start the oscillation. I added the .IC condition at node 3 (non-inverting input to op amp). This is equivalent to starting the circuit with some charge on C1. With the initial condition the circuit oscillates cleanly.

  

These images are from a LabVIEW program which plots the results generated by the Spice simulator. The LV program has much more flexibility in plotting than the Spice program.  The Spice listing is attached.

Lynn

[radiola18]

Looks good, Great to see you got it working! So what your kind of saying is that if I want to run these sort of simulations in my simulator. I need to figure out how to do a  transient simulation or analysis.

Warm Regards,

Derek

[johnsold]

Derek,

Transient analysis tells you what happens over time.  That is what an oscillator does: It converts the energy from the DC power supply into a periodic time varying signal.

An AC analysis tells you how the small signal behavior of the circuit varies with frequency. To do an AC analysis the circuit must have an independent  source with an AC value specified.  Normally you would not have an AC source in an oscillator circuit.

Multisim (I think) is Spice-based, but I have no idea of how they do various kinds of analyses or what restrictions may apply.

Lynn

[radiola18]

Thank you for clarifying that for me. Makes perfect sence. i think I saw the right test in my program menu, I just need to set the time parameters.

I tried to attach some screen shots, I hit browse, click my doc, hit open, shows up C:\Users\Derek\Documents\Multisim 12 Screen Shots\Screen Shots.docx in the Attachments box. hit post. It disappears from the Att. box. If I hit post again it will just post my comments.

Warm regards,

Derek

[johnsold]

Try .png files for screen shots.  They attach fine.

I seem to recall that some people have been having trouble with IE8 and attachments.  Read that thread to see if there are any work arounds that you cna use.

Lynn

[MathanKamlesh]

Greetings. Im raj.Sir im a student, I also do the same circuit sir. I try draw and simulate using multisim but i didnt get the sine wave.Could you please help me to solve the problem. i attach my drawing and simulation result too.Tq

[johnsold]

Did you try the initial condition method I suggested above?

Lynn

[MathanKamlesh]

Thanks for the reply sir. Sorry sir. I do not much understand about the initial condition. So can you please explain the initial conditions again.Sir im using multisim software. So that i can apply the conditions in multisim software. Thanks again

[johnsold]

I do not have Multisim, so I cannot tell you exactly how to do this with that program. In SPICE you can use the .IC (initial condition) command to set a starting voltage on one of the timing capacitors.  Also, you must be doing a transient analysis, not an AC analysis.

Lynn