# How to analyze this oscillator?

Discussion in 'Electronic Basics' started by Archer, May 7, 2004.

2. ### Michael BlackGuest

It's an odd circuit, and I can't help but wonder if wherever you found it,
they might have copied it wrong.

The left hand op-amp is clearly a a low pass filter. The second stage is
clearly an integrator. There is enough shift through those two stages so
bringing the output of the second stage to the input stage makes the thing
oscillate. The zener diodes limit the output of the second stage, may even
square up the signal (in one direction, one zener is merely a forward biased
diode with about .7v drop and the other zener is acting like a zener,
conducting when voltage across it reaches the voltage where it "zeners",
then when polarity is reversed, the roles of the diodes reverse).

But I can't say I've seen this particular circuit before. It seems
a bit odd.

Usually, when a quadrature oscillator is needed, you see two integrators
in a similar circuit, each providing 90 phase shift (and so two stages
in series provide 180 degrees of shift, and that fed back to the input
makes the whole thing oscillate).

Michael

3. ### ArcherGuest

Thank you,Michael!
I found this oscillator circuit on "The Art of Electronics".
I wanna to analyze it and design an oscillator which is using a
quartz crystal to get excellent frequency stability,so i analyze
this circuit using algebra method with its model. but i can't
find any power supply or Vin in this.

4. ### benchGuest

Thank you,Michael!
If you found it it that book it is most likely correct. My advise to
you is to build it and see what happens, or simulate it with
Circuit Maker 6 or whatever. Since it is an oscillator, there should
be no power input only output, of course the op amps will be
powerd up as usual, probably with a +-18V supply.

5. ### benchGuest

b.t.w. what page did you find it at?

6. ### ArcherGuest

At the end of charpter 5 about active filters and oscillators.
Page.304

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