Requests for information

MrChips

Joined Oct 2, 2009
21,121
Off the top of my head, one simple explanation is - crystals are tuned circuits. Loading capacitors help to lock in to the resonant frequency.

Another reason is - crystals have different modes of oscillations, most commonly, fundamental and third harmonic.
Capacitors help the crystal to oscillate at one preferred frequency.

You can read this:
http://www.ti.com/lit/an/swra372c/swra372c.pdf
 

Dodgydave

Joined Jun 22, 2012
9,161
The capacitors are there to resonate with the crystal inductance and cause the crystal to oscillate on its fundamental parallel-resonant mode. ... The difference between a crystal with two capacitors compared to a ceramic resonator is that the capacitors happen to be integrated into the ceramic resonator.
 
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