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why a crystal of 49.152M oscliate at 16.3M?

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xianweng

xianweng

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Hi ,everybody
When I used a crystal of nominal frequency at 49.152M and two capacitance with a chip to form the pierce oscillator,is oscillates at 16.3M. It is weird. Inverter and the bias resistor has already integrated in the chip. I used two different types of oscilloscope with different probes to measure,but the result is the same. And i changed the capacitance ,the result is also same.I also changed the crystal ,but the result is the same
The fundamental frequency of crystal is 49.152M
Could anybody help me figure it out?Thanks any help in advance
 
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It is for sure an overtone crystal.

This means that the crystal is ct at 1/3 of the oscillating frequency, but if you select the proper harminic, it will oscillate three times the natural frequancy.

Due to parasitics, the natural frequency is not exactely 1/3 of the overtone frequency.

Mandi
 
I do not have the datasheet of crystal and do not know what kand of brand it is. But there is "49.152" carved on the package.

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FvM said:
How do you know that it's not an overtone crystal?
Click to expand...
I do not have the datasheet of crystal and do not know what kand of brand it is. But there is "49.152" carved on the package.

- - - Updated - - -

FANT said:
It is for sure an overtone crystal.

This means that the crystal is ct at 1/3 of the oscillating frequency, but if you select the proper harminic, it will oscillate three times the natural frequancy.

Due to parasitics, the natural frequency is not exactely 1/3 of the overtone frequency.

Mandi
Click to expand...
Maybe you are right.I will buy some new crystal
 

There are means to force the crystal to oscillate at the overtone, e.g. a parallel LC circuit tuned to the overtone or a series LC tuned to the unwanted fundamental.
 
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