Short Transmission Line Model

I would like to know the electrical model of a trace in a PCB. That is, where is the inductance, the capacitor and the resistance.

Thank you.

Thanks for your interest in High-Speed Digital Design.

A good model for a SHORT transmission line is formed from four components: This circuit, called a pi-model, mimics the behavior of one short section of a transmission line

Where the ground node really refers to the nearest solid reference plane, regardless of voltage.
Where the values of C1 and C2 are the same, and equal to dly/(2*Z0), where dly is the line delay in pico-seconds, Z0 is the characteristic impedance of the line in ohms.
Where the value of L1 equals dly*z0
Where R1 is the resistance of the line (for short lines on PCB's we usually assume 0.000 ohms)


The Pi-model is accurate to about +/- two percent if the line delay is less than 1/6 of the signal risetime.

The Pi-model is accurate to about +/- twenty percent if the line delay is less than 1/3 of the signal risetime.

If the line delay stretches as far as 1/2 the signal risetime you can get huge unpredictable resonances and all bets are off. The model fails.

Best Regards,
Dr. Howard Johnson