Microstrip crossover

QuickField simulation example

Crossovers in the digital circuit design cause parasitic capacitance, resulting in high frequency cross talk.

Engineering question
How to find PCB microstrip crossover capacitance?

Engineering answer
Set up a 3D QuickField Electrostatics problem for a PCB microstrip crossover and evaluate capacitance from computed field results.

Typical applications
PCB microstrip crossovers, multilayer PCB crossings, signal routing crossovers

• Download simulation files (files may be viewed using any QuickField Edition).

Problem Type electrostatics.

Geometry 3D extrusion.

Equivalent electric circuit:

Given
Relative permittivity of air ε = 1,
Relative permittivity of substrate ε = 10,
Strip1 potential U1 = -0.5 V,
Strip2 potential U2 = +0.5 V.

Task
Find the mutual capacitance between strips C12.

Solution
To find the mutual capacitances C12 we should switch off all voltage sources and apply opposite potentials on stip1 and stip2.

QuickField simulation gives charge q distribution. The capacitance then can be calculated as C = q / (U2 - U1).

Results
The measured charge q = 1.76e-12 C.
The capacitance is C12 = 1.76e-12 / (0.5 - (-0.5)) = 1.76e-12 F.

• Video: Microstrip crossover. Watch on YouTube