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(Obsolete) Thin Film Resistor Distributed Lossy Line Model (Closed Form): TFR

Symbol

Summary

This element is OBSOLETE and is replaced by the Thin Film Resistor Distributed Lossy Line Model (Closed Form) (TFR2) element.

Parameters

Name Description Unit Type Default
ID Name Text TL1
W Resistor width Length W[1]um
L Resistor length Length L[1]um
RS Sheet (surface) resistivity   50
F Frequency for scaling sheet resistivity Frequency 0
MSUB Substrate definition Text MSUB[2]

[1] User-modifiable default. Modify by editing under $DEFAULT_VALUES in the default.lpf file in the root installation directory.

[2] If only one MSUB is present in the schematic, this substrate is automatically used. If multiple MSUB substrate definitions are present, you must specify which to use.

Implementation Details

This circuit component models a thin film resistor as a lossy microstrip line with the complex characteristic impedance.

The parameters W (width), and L (length) are dimensions entered in the default length units. The parameter MSUB specifies microstrip substrate element, which defines additional cross sectional parameters of the transmission line. If blank, a default is used.

If parameter F is set to zero, then sheet resistance RS stays constant with respect to frequency. This holds true if thickness of the resistive film that makes resistor body is less than skin depth.

If thickness of resistive film exceeds skin depth the sheet resistance RS may be scaled with frequency in accordance with the formula:

User can activate this scaling by setting F≠0 . In this case F should be evaluated by user in advance as

where σ - bulk conductivity of the resistive film in S/m and t - thickness of the resistive film in microns. If F is set in accordance with this formula scaling of RS is implemented only for F >f; for f<F RS stays constant.

Note that you must enter the actual value of parameter F in default frequency units.

For most cases frequency F is very large (for example, hundreds gigahertz) and setting F=0 is the best choice.

The component accounts for losses in metal and in substrate dielectric. Dispersion is included.

Layout

The layout for this cell has hard-coded model layers. When you first use this layout cell, layers named "NiCr" and "Metal1" are added to your drawing layer and model layer list (if they are not already there). Using the model layer mapping, you can assign these layers to draw on any drawing layer. The resistor material is drawn on the "NiCr" model layer and the resistor pad is drawn on the "Metal1" model layer. The metal overlap of the resistor is hard-coded as 3 um and the resistor material extends 3 um under the metal pad, therefore, the metal pad length is 6 um and the width is the width of the resistor plus 6 um.

References

[1] E. Hammerstad and O. Jensen, "Accurate Models for Microstrip Computer-Aided Design," IEEE MTT-S International Microwave Symposium Digest, 1980, pp. 407-409.

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