# [SI-LIST] Re: Odd mode impedance

• From: Ray Anderson <Raymond.Anderson@xxxxxxx>
• To: si-list@xxxxxxxxxxxxx
• Date: Tue, 25 Jun 2002 10:52:46 -0700 (PDT)

```
>
>Hi,
>I have a pair of 11mils wide microstrip lines with 8.7 mils separation and 5
>mils FR4 substrte thickness. Can anybody help me calculate or suggest me an
>appropriate tool to calculate the odd mode impedance?
>Regards,
>Mir
>
>

Differential impedance (assuming condition above) =  73.59 ohms
Common mode impedance (assuming condition above) =  22.14 ohms

The full output is:

---------------------------------------------------------------------
RLGC MATRICES FOR GENERAL CONFIGURATION

*title: test2

Frequency = 1.000e+08 Units = mil

Method used = 1 (default is 1)

epsr1 = 1.000e+00 tand1 = 0.000e+00 height1 = 0.000e+00
epsr2 = 4.600e+00 tand2 = 1.800e-02 height2 = 1.400e+00
epsr3 = 4.600e+00 tand3 = 1.800e-02 height3 = 5.000e+00

Number of traces in conductor 1 = 1
layer1 = 2, widthBottom1 = 1.100e+01, widthTop1 = 1.100e+01,
xcord1 = 0.000e+00, sigma1 = 5.800e+07

Number of traces in conductor 2 = 1
layer1 = 2, widthBottom1 = 1.100e+01, widthTop1 = 1.100e+01,
xcord1 = 1.970e+01, sigma1 = 5.800e+07

Bottom ground plane thickness = 7.000e-02;
Conductivity of Bottom ground plane = 5.800e+07

CMATRIX (F/mil) =
4.036e-15 -2.376e-16
-2.376e-16 4.036e-15

CMATRIXAIR (F/mil) =
1.109e-15 -1.381e-16
-1.381e-16 1.109e-15

LMATRIX (H/mil) =
6.572e-12 8.180e-13
8.180e-13 6.572e-12

GMATRIX calculated at a frequency of 1.000e+08

GMATRIX (S/mil) =
4.215e-08 -1.501e-09
-1.501e-09 4.215e-08

RMATRIX calculated at a frequency of 1.000e+08

RMATRIX (ohm/mil) =
6.225e-04 1.367e-04
1.367e-04 6.225e-04

CHARACTERISTICS OF VARIOUS MODES

Mode #       Z0          Effective Relative    Attenuation
(ohms)        Dielectric Constant     (dB/mil)

1      36.79-j2.16            3.44            6.434e-05
2      44.28-j3.22            3.93            8.232e-05

For two identical conductors symmetric with respect to ground,
the differential and common mode impedances are defined.

Differential impedance (assuming condition above) =  73.59 ohms
Common mode impedance (assuming condition above) =  22.14 ohms

CHARACTERISTIC IMPEDANCE MATRIX (ohms):

Real part  =
4.054e+01 3.745e+00
3.745e+00 4.054e+01

Imaginary part  =
-2.689e+00 -5.284e-01
-5.284e-01 -2.689e+00

FORWARD CROSSTALK COEFFICIENT MATRIX (ns/mil):

Real part  =
1.625e-04 5.450e-06
5.450e-06 1.625e-04

Imaginary part  =
-1.344e-05 -1.648e-06
-1.648e-06 -1.344e-05

BACKWARD CROSSTALK COEFFICIENT MATRIX :

Real part  =
1.000e+00 4.658e-02
4.658e-02 1.000e+00

Imaginary part  =
0.000e+00 -3.487e-03
-3.487e-03 0.000e+00

The forward and backward crosstalk matrices can be used to get
approximate crosstalk information. See manual for details.

CHARACTERISTICS OF INDIVIDUAL LINES FROM DIAGONAL ELEMENTS OF RLGC MATRICES.
COUPLING IS NEGLECTED IN THE INFORMATION GIVEN BELOW

Line #        Characteristic Impedance     Delay     Attenuation
(ohms)              (ns/mil)     (dB/mil)

1                40.49-j2.70          1.632e-04    7.422e-05
2                40.49-j2.70          1.632e-04    7.422e-05

----------------------------------------------------------------------

-Ray Anderson
Sun Microsystems

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