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momentum vias

Question asked by MESFET98 on Oct 24, 2003
Latest reply on Oct 26, 2003 by ALEPEREZ

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Hello,

I simulated a cylindrical via in momentum with the following dimensions:

Height= 8mils
Diameter=8mils
Via pad (square)=13.5mils
Metal thickness=1.4mils

Substrate parameters are
GETEK
Dielectric constant=3.83
Loss tangent=0.008
Configuration of the substrate is:
Strip METAL
GETEK dialetric VIA
GROUND

I then simulated in ADS a VIA2 component (with the same dimensions) from the Tlines Microstrip Palette.

The inductance given by momentum was different than the inductance given by the VIA2 component.

Inductance of via (momentum)=58.7pH
Inductance VIA2 =21pH

Why is that?

I would expect them to be the same.

Any clues?

Thanks

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ALEPEREZ Oct 26, 2003 10:48 PM
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The Via2 model should be quite accurate within the model range limits given in the manual. Even outside these limits, I have seen that the model is still close - that is, the accuracy does not diminish radically as you go outside of the model bounds. Therefore, the large discrepancy of inductance you report is more likely related to how the reference plane was chosen in the Momentum analysis, the port type (Single required in this case) and the equation used to extract L. Frequency will also play a role due to the transition of DC to high-frequency loss/inductance.

Momentum may underestimate the low-frequency inductance by about 10% because it assumes current to always flow on the surface of the via, never distributed evenly inside the via as it would be at low frequencies.

The best way to solve your problem would be if you could package up the project as a *.zap file (Archive Project command) and send it to technical support.
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