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Crystal's motional capacitance?

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shockoshocko

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I am trying to simulate a 40 MHz parallel mode crystal oscillator, but most crystals vendors don't specify motional capacitance or inductance, I realize that if I have either motional capacitance, inductance, quality factor or series resonance frequency, other parameters can be calculated, but vendors don't specify any of these.

datasheet: https://www.euroquartz.co.uk/Portals/0/mq.pdf

Note: I don't have the crystal to make any measurements, I only want to simulate it.
 

You need the specific crystal to be very accurate. 40 MHz is pretty high freq for a fundamental mode xtal. Cm will likely be in the 2.5 to 3.0 fF range with Rs in the 30 ohms range.

Simulating crystal oscillators is very tricky. Without some extra startup excitation injection your simulation will likely run for a long time before you see anything. You start to wonder if it is ever going to start up and your circuit design has issues. You have to know how to inject a startup signal so it has little impact to the true steadystate oscillation.

A 40 MHz fundamental parallel mode will take about 200 to 300 usecs to start up in real world depending on oscillator circuit design. This amount of time is an eternity in simulation time.
 

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