I am trying to model a PCB trace as a R, L, C circuit.
Assumption: My PCB has a a single trace running through it. Just giving input from one side and taking output from other. There is not even a GND plane. There is a seperate wire outside the PCB to complete the circuit and provide the return path. Let's even assume that the outer wire is completely ideal (no losses).
Now, the power is surely going to drop over long distances, which will be total drop over R, L and C. If I were to model it as a R, L, C circuit:
- What will be the dielectric constant and permeability constant for a top layer trace?
- Will it be that of copper? I have seen an effective dielectric constant of around 3 being used for microstrips accounting also for air. But, the doubt is, in general PCBs have stray capacitances, coupling capacitances etc. thus making it an effective dielectric constant, while in the above case, none of them exists.
- What will be the case for an middle layer trace?
Dielectric constant for FR4=4.3, but copper is continous right, So why not to use that of copper?
Thanks in advance!
If I change the model to that of a single conductor on a PCB, (like a part of some larger circuit is on the PCB, so the circuit is complete), will that help?
How to calculate R, L and C values in that case for both top layers and middle layer?
What will be the dielectric and permeability constants in such cases?
Point is not to use rule of thumb but to understand the basics of PCB layout.