Many more structures are available for a monthly or annual subscription price. The microstrip and stripline structures are available for free to any visitor after a brief registration. An example of the parameterized differential stripline. These are pre-defined topologies, such as shown in Figure 1.įigure 1. The free version allows calculation of simple single-ended and differential microstrip and stripline structures. While there are many 2D field solvers available, many are either bundled inside expensive tools, or have a user interface with a steep learning curve.
This is why a 2D field solver should be used as your design tool of choice. These tools are limited to the numerical accuracy of solving Maxwell’s equations, which generally are accurate to better than 1%. Since the calculation is based on arbitrary geometries, it can include all the important second order geometry features such as adjacent ground or other traces, trace thickness, etch back, and soldermask. And they do not include the impact from second order factors like etch back and solder mask.Ī calculator based on a 2D field solver will solve Maxwell’s equations using the boundary conditions of the geometry and the material properties you give it to calculate the inductance and capacitance per length of the transmission line and from these, the characteristic impedance. But for extreme geometries and for many differential pair structures, these approximations can be off by more than 20%. Near 50 ohms, many of these approximations are within a few percent accurate. While there are a number of online calculators that calculate the characteristic impedance from the input geometry, they are all based on approximations.
It depends only on the cross section of the transmission line and the material properties.
There is one value of instantaneous impedance that characterizes the transmission line, which we call the characteristic impedance. In a uniform cross section transmission line, a propagating signal sees the same instantaneous impedance down the line. Who doesn’t love an easy-to-use 2D field solver to calculate the single-ended or differential impedance of PCB transmission lines? Now there is a new one available, recently released by Sierra Circuits, a leading fab shop for advanced and quick turn PCBs.
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