pcb trax to transmition line impedence count

txline differential impedance zip

is there any short way to count the impedence of any trax? Is there any simulation for it? soem of the calculation take too longs...

The impedance of a PCB trace depends on its width, thickness, cross sectional shape, distance to the signal return path (usually an underlying plane), and the dielectric constant of the material above and below the trace.

There is no "rule-of-thumb" shortcut for getting an accurate calculation of the trace impedance. However, once you have calculated the value for a trace on a given board layer, you don't need to repeat it again for other traces on the same layer. You just keep the controlled traces all the same width on that layer.

There are MANY calculators available free on the Internet. If you are not doing a critical application, any of those calculators will get you within about 10-15 percent of the trace impedance you want. If you need accuracy better than that, you will have to use a field solver to do the calculation.

Some free calculators that will give decent approximations are:
**broken link removed**
http://www.ultracad.com/diff_calc.htm
http://transcalc.sourceforge.net/
http://www.appwave.com/src/products/TXLine.zip

thx very much..! that will be a lot easier

I would not recommend using the UltrCad differential impedance calculator, bought or otherwise - for some reason it is based on the flawed theory that the separation between the +/- legs of a differential pair have no bearing on the impedance - a highly disregarded theory, based on an assumption that a stripline trace represents essentially the same characteristics as a coaxial condutor - IE: if you have 2 50 ohm caxial cables the differential between the two is a constant 100 ohms regardless of the separation - this is simply not true in a PCB.

SiGiNT

Good point regarding differential traces, Sigint - when I recommended the ULTRACAD calculator, I was thinking more of the microstrip and stripline calculator for his use. ULTRACAD has rolled their old single-ended calculator into the free version of their differential calculator. You don't get the differential version unless you pay.

For differential pair calculations, I use a field solver. There isn't any free calculator that can do the job accurately.