I have a 4Mhz crystal and i connect it in series between the function generator and the oscilloscope probe as shown below:


simulate this circuit – Schematic created using CircuitLab

However i don't know if this testing method for XTAL is true or not but to see if the crystal works or not i set the function generator on 5Vpp and start to increasing the frequency, i was expected to see some change in the output in 4Mhz, but just when the frequency reach 4MHz i find the voltage in the output become 50Vpp !

I know the resonance causes increasing the voltage but there are no Inductor in this case,

So i'm wondering why this happen without inductor?


1 Answer 1


There is effectively an inductance, caused by the mechanical arrangement of the piezelectric crystal, called the "motional inductance".

Here is an LTspice model of a 4MHz crystal using values for an ECS 4.000MHz crystal.

enter image description here

I have simulated your probe with a 10M\$\Omega\$ resistor in parallel with 3pF. Crystal parameters from this page.

The resulting Bode plot is here:

enter image description here

The peak output is about +30.6dB at the resonance, which is even more than you are seeing.


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