Electrical – shunt capacitance the same as stray capacitance

A good tip for getting optimum cap values is that an oscillator like this is happiest when the amplitudes of the signals at each side of the crystal are similar. PCB capacitance will be a factor, so this needs to be tweaked on the actual board, and using a x100 scope probe to avoid the probe affecting the reading. A 10M resistor right on the tip of a standard probe is an alternative if you don't have a x100 - accuracy doesn't matter as you're just looking at relative amplitudes.

can i calculate it by altium? if yes, how?

I can't answer that.

if no, please provide a program untill i use it for solve my problem.

I assume your PCB trace is micro strip. You can use this calculator for example.

Fill in the required parameters:

• W[m] width of the trace
• H[m] height of dielectric above return plane
• T[m] trace thickness
• Er[ ] relative permittivity of the dielectric

H is the distance between the trace and the GND plane below it. It depends on you PCB layer stack up.

Er depends on the dielectric of the PCB. Its About 4.3 for FR4. Look at the technical specifications from your PCB manufacturer.

As a result you get

• [F/m] capacitance per unit length

which is what you want. Be careful to convert all the values to SI-Units as required by the calculator from the example.