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Crystal circuit question

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difflvl

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Hi,

I have tried searching google but I haven't found my answer.

What role do R1 and R2 play in this circuit? What is the difference between the two circuits?

How does having R1 and R2 effect EMI and and FCC part 15?

Thanks
 

The parallel resistor is a biasing feedback resistor to help the crystal circuit to oscillate when used with logic gates or inverters. It provides linear operation. The series resistor limits crystal dissipation which is not good for minimizing long term frequency drift and aging.
 

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    difflvl

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I have read that R2 is supposed to slow the rise time. Is this true? How can I measure the rise time?

Thanks
 

R1 may lower the Q of the oscillator.
The rise time I think it's the rise time of the generated wave form ,whose frequency determined by the crystal. So here's something with EMC and EMI, short rise time introduce more harmonics and frequency expansion.
 

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    difflvl

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