# XTAL resonance increase the voltage

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?

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.

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:

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