University of Missouri-Rolla offers PCB trace impedance and inductance calculators

The University of Missouri at Rolla provides an on-line "PCB Trace Impedance Calculator" and an "Inductance Calculator." The PCB Trace Impedance Calculator will calculate the impedance of microstrips, embedded microstrips, striplines, and asymmetric striplines (noting, of course, that the results are only approximate). The inductance calculator will handle square loops, rectangular loops, circular loops and even triangular loops. Check out the impedance calculator at: www.emclab.umr.edu/pcbtlc/index.html.

The transmission line calculator concept was developed by Douglas Brooks and is described in his paper: "PCB Impedance Control: Formulas and Resources," Printed Circuit Design Magazine, March 1998. A copy of his paper and a similar transmission line calculator that runs on a PC can be obtained from www.ultracad.com. These formulas are approximations and should not be used when a high degree of accuracy is required.

Inductance calculator
The transmission line geometries are cross sections and the values calculated are the inductance per unit length and can be found at: http://emcsun.ece.umr.edu/new-induct/. In all cases, the current is assumed to flow in the outer surface of the conductors. The approximate formulas used to calculate the inductance are provided along with restrictions on the relative size of the various parameters. These formulas can be found in various texts and most of them are derived in the book "Inductance Calculations" by F. W. Grover.

Other calculators can be found at: http://www.emclab.umr.edu

Edited by Paul O'Shea
Managing Editor, TestandMeasurement.com