# How to simulate parasitic reactances in a circuit

Does parasitic capacitance of a microstrip trace add to the value of a physical capacitor on the same trace?

If one sees it as a series element, then it would seriously reduce the value of all capacitors that has a bigger capacitance value than the trace. If one sees it a parallel element, then the trace capacitance would add to the value of the capacitor. I guess the latter must be right, but I'd really like to get some opinions on how this works.

The same goes for inductors.

## 1 Answer

Parasitic capacitance absolutely adds to the value of a physical capacitor on the same trace (same goes for inductors and resistors!).

In a microstrip the parasitic capacitance is to the shield layer (typically ground). So that would be a parallel capacitor and would add.

Likewise, the inductance is due to the trace itself (self-inductance) and also might have some mutual with other traces. It is a series component that adds to the inductance of the trace.

A good rule-of-thumb if you're confused is that parasitics on a signal trace will make matters worse, whether for capacitance, resistance, or inductance.