Accuracy of IPC Formula
CHAPTER 44.11 2Accuracy of IPC Formula with respect to the 2D Field Solver
We have attempted to list the value of the capacitance per unit length value obtained from the formula method and compare it against the 2D Field solver method using hspice.
The Table below lists the value calculated from hspice 2D field solver vesus the IPC formula.
Table 4 1 – Comparison of Impedance Calculation
From the table we see that the formula method from the IPC vary as much as 13%. The IPC formula method should therefore only be used only to get a preliminary estimate. The IPC formula works better near the cases where the characteristic impedance of the transmission line is near 50 Ohms. This method is not suitable for, for example, the calculation of trace impedance of power supply traces.
Let us take a look at the line
+ Co = 9.477066e-011
This line gives the capacitance per unit length in Farad per meter. If we convert it into pf/inch, the result is 2.407 pf/inch. The result obtained by the IPC formula method is 2.444. In this particular case the difference in the formula method and the 2D field solver method is only about 1.5%.
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