Xtal oscillator using LM311

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GGAPBE96

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Hi there,

I'm trying to design a crystal oscillator by refering the document.

**broken link removed**
(Please see "9.0 Typical Applications" 100kHz crystal oscillator)

However,I can't understand the oscillation mechanism.
How does the oscillator work??

I think 100kHz crystal and 10pF makes positive feedback.
What does C2 do??
 

C2 provides the crystal's specified load capacitance and also works as a voltage divider. If You don't understand the circuit
or doubt it's not suitable, use a different one from a text book.

P.S.: I think a crystal oscillator with a high-pass feedback is at risk to fall into overtone oscillations, if the modes are not
well supressed in crystal design. I would prefer an unbuffered CMOS gate as crystal oscillator.
 

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    GGAPBE96

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FvM, thank you so much.
So far, overtone oscillation does not occur.

Sorry,I mistook my question..
What I wanna ask is not the role of C2 but the role of C1.
It seems to be irrelevant to positive feedback.
 

GGAPBE96 said:
............
Sorry,I mistook my question..
What I wanna ask is not the role of C2 but the role of C1.
It seems to be irrelevant to positive feedback.
Click to expand...

Yes, but don't forget negative feedback.
R3 provides 100% feedback for dc. That's necesssary for opamp biasing.
However, for frequencies in the region of oscillation the negative feedback must not dominate - otherwise the circuit wouldn't oscillate.
Thus, the inverting input has to be ground referenced for these frequencies.
That`the task of C1.

By the way: As C2 is connected in series with the crystal, the crystal operates in its inductance region (series resonance with C2).
 

    G

    GGAPBE96

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Thank you for the quick and kind explanation.
Now I understand the circuit.
 

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