Today I came across this design(as I am studying for my exams :P)(adsbygoogle = window.adsbygoogle || []).push({});

And looking through my good Malvino, I found it. And I my mind was simply blown out by the concept of this oscillator. (If I got it right)

http://pokit.org/get/957089cb8862c381d597a745b02c2763.jpg [Broken]

Malvino went here and there, but in a nutshell is this what is happening:

We get some thermal noise from that R1. But that part of the op-amp, which has negative feedback is not so much effective like the positive feedback part.

Thermal noise covers a lot of frequencies(over 1 THz), with that positive feedback resonant circuit, we are picking which frequencies we want.

As time goes by, more and more voltage we get across the output. Then negative feedback path kicks in and doesn't let it go to infinity, but "drowns" it back to unity.

For oscillations to continue, 2*R1 must be greater than R2. Then the op-amp feeds itself with that oscillation.

Now correct me if I am wrong, but did we get a fairly good oscillator(used almost in every car, I read that, I don't know for what) just from the starting thermal noise?

If it is, I find that most amazing thing I learned about op-amps...

**Physics Forums | Science Articles, Homework Help, Discussion**

Dismiss Notice

Join Physics Forums Today!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Wien-bridge oscillator

**Physics Forums | Science Articles, Homework Help, Discussion**