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.
Thanks for your interest in High-Speed Digital Design.
A good model for a SHORT transmission line is formed from four components:
Where the ground node really refers to the
nearest solid reference plane, regardless of
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.
Dr. Howard Johnson