# LC oscillator op-amp

Discussion in 'Homework Help' started by Thomas Nes, Jun 11, 2015.

1. ### Thomas Nes Thread Starter New Member

Jun 11, 2015
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Hi all,

Could someone explain the attached circuit for me? This is what I know or believe to know: It is an LC oscillator, which gets excited by noise and creates a sine wave at the output of the op-amp. The op-amp gives positive feedback and amplifies the oscillations, making sure they won't die out. Also the diode part is to counter clipping of the signal. But how does this positive feedback exactly work? What is the gain of this circuit and how do I calculate it. Why does the clipping happen and how does this diode bridge exactly prevent this? And what is the exact function of the resistances R1 to R3?

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2. ### MikeML AAC Fanatic!

Oct 2, 2009
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What is the closed-loop gain of the opamp between the non-inverting input and the out put assuming the signal there is too small to make the diode(s) conduct?

What is the closed-loop gain of the opamp between the non-inverting input and the out put assuming the signal there is large enough to make the diode(s) conduct?

What is the Barkhausen Criterion?

Last edited: Jun 11, 2015
3. ### JoeJester AAC Fanatic!

Apr 26, 2005
4,074
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What is the source of that circuit?

4. ### MikeML AAC Fanatic!

Oct 2, 2009
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1,075
Here is something for you to explain. For simulation, the circuit has to be initially perturbed: .IC V(n)=10pV

The first is the startup behavior. Note when current begins to flow in R4.

The second is a cycle once oscillations stabilize. Note the two voltages and the current in R4.