0
\$\begingroup\$

Both the lumped parameters models vs transmission line models use RLC components for modelling.

This is where I am confused and cannot see the difference between the two.

\$\endgroup\$
7
  • \$\begingroup\$ One is an approximation that serves well at lower frequencies and the other shortens the lumps into zero lengths and therefore predicts the transmission line characteristics at all frequencies. If my comment doesn't make sense than maybe try to explain a little more about your confusion. \$\endgroup\$ – Andy aka Jan 29 at 9:17
  • \$\begingroup\$ @Andyaka You said LP serves well at low frequencies but what if I use equivalent circuits to model frequency dependent behavior of a circuit (instead of one LP resistance that models skin and proximity effect for example, use and equivalent RLC circuit), does this not serve the high frequencies? \$\endgroup\$ – Wallflower Jan 29 at 9:28
  • \$\begingroup\$ I have no idea what you mean. I offered my comment to provoke you into explaining in more detail what your confusion is about and, until I understand that, there's no point me trying to 2nd guess anything. \$\endgroup\$ – Andy aka Jan 29 at 9:31
  • \$\begingroup\$ @Andyaka I have a conductor that I want to model. Two models are used: either Lumped parameter model or transmission line model. When I research the two, I cannot seem to understand the difference between the 2, since they both use RLC parameters and which one the two will be more suitable for my conductor modelling. PS: frequency behavior is supposed to be taken into account by my model (skin and proximity effect as well as flux penetration) \$\endgroup\$ – Wallflower Jan 29 at 9:34
  • \$\begingroup\$ Well, you know what the two models are but, nobody at the other end of the internet (such as me or someone else reading your question) does so I don't see how anyone can help you very much without you revealing more information. \$\endgroup\$ – Andy aka Jan 29 at 9:41
1
\$\begingroup\$

A lumped parameter model uses R, L and C components connected together at nodes. Nodes have zero electrical length, zero capacitance to ground, and so enforce the same voltage at all times at all component terminals connected to them, and a net current flow of zero into that node. We often show nodes on schematics as wires. At low frequencies, and for short wires, we will often approximate real wires in a circuit as nodes.

A transmission line model uses R, L and C components connected together with transmission lines. These lines have distributed capacitance to ground, and a distributed inductance. At high frequencies, and for long wires, real wires are better approximated by transmission lines. The voltage at each end of a line can be different, and the total current into both ends of a line need not be zero, a signal will take a finite time to travel from one end of the line to the other.

For limited frequency ranges, for either conceptual or simulation convenience, we can approximate a transmission line as a cascade of LC sections, and add shunt or series R to the sections if we want to simulate losses.

\$\endgroup\$
3
  • \$\begingroup\$ When you say zero capacitance to the GND for the lumped parameters (LP) model, what if I add a C//R to model the coupling of the conductor I modelled using LP to model its coupling to the GND? \$\endgroup\$ – Wallflower Jan 29 at 9:26
  • \$\begingroup\$ @Wallflower ... then you've added explicit components, and they'll behave as components behave. A transmisson line has these components built in. A wire or node does not. \$\endgroup\$ – Neil_UK Jan 29 at 10:30
  • \$\begingroup\$ Understood, thank you! \$\endgroup\$ – Wallflower Jan 29 at 11:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.