2D Field Solver for Calculating Capacitance
CHAPTER 44.11 2D Field Solver for Calculating Capacitance
The 2D Field solver is used to get more accurate result of the capacitance per unit length. As an example, the following hspice code can be used to calculate the capacitance per unit length of a microstrip structure.
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* W element, field-solver interface * XXXXXX * ------------------------------------ Z = 5mils * Er = 4.3 H = 4mils * ------------------------------------ Z = 1mils * //// Bottom Ground Plane /////////// * ------------------------------------ Z = 0 W1 in1 0 out1 0 FSmodel=demo N=1 l=0.97 * Materials .MATERIAL copper METAL CONDUCTIVITY=5.76e+07 .MATERIAL diel_1 DIELECTRIC ER = 4.3 LOSSTANGENT=1.2e-3 CONDUCTIVITY=8.2e-4 * Conductor cros section shapes .SHAPE rect RECTANGLE WIDTH = 5mils HEIGHT = 1mils * Dielectric stack-up .LAYERSTACK Stack + LAYER = (copper, 1mils) + LAYER = (diel_1 4mils) * Field-solver options .FSOPTIONS myOption ACCURACY = LOW GRIDFACTOR = 1 + ComputeRo=yes ComputeRs=yes ComputeGo=Yes ComputeGd=yes PRINTDATA=YES .MODEL demo W ModelType=FieldSolver + LAYERSTACK=Stack FSOptions=myOption + RLGCFILE= rlgc_5_mils.txt + CONDUCTOR = ( MATERIAL=copper, SHAPE=rect, ORIGIN=(1000mils, 5mils) ) *Analysis .tran 0.1ns 100ns .option post .end |
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*SYSTEM_NAME : demo * * Half Space, AIR * ------------------------------------ Z = 1.270000e-004 * diel_1 H = 1.016000e-004 * ------------------------------------ Z = 2.540000e-005 * //// Bottom Ground Plane /////////// * ------------------------------------ Z = 0 * L(H/m), C(F/m), Ro(Ohm/m), Go(S/m), Rs(Ohm/(m*sqrt(Hz)), Gd(S/(m*Hz)) .MODEL demo W MODELTYPE=RLGC, N=1 + Lo = 3.447940e-007 + Co = 9.477066e-011 + Ro = 5.381888e+000 + Go = 1.656011e-003 + Rs = 2.132704e-003 + Gd = 3.572770e-013 |
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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