URC - Uniform Distributed Lossy Line Model

Model Kind

Transmission Line

Model Sub-Kind

Uniform Distributed RC

SPICE Prefix

U

SPICE Netlist Template Format

@DESIGNATOR %1 %2 %3 @MODEL L=@LENGTH ?"NO. SEGMENTS"|N=@"NO. SEGMENTS"|

Parameters (definable at component level)

The following component-level parameters are definable for this model type and are listed on the Parameters tab of the Sim Model dialog. To access this dialog, simply double-click on the entry for the simulation model link in the Models region of the Component Properties dialog.

Parameters (definable within model file)

The following is a list of parameters that can be stored in the associated model file:

Notes

1. The model is derived from a model proposed by L. Gertzberrg. The model is accomplished by a subcircuit type expansion of the URC line into a network of lumped RC segments, with internally generated nodes. The RC segments are in geometric progression, increasing toward the middle of the line, with K as a proportionality constant. If a value for the number of lumped segments to be used in modeling the line is not specified, it will be calculated using the following formula:

N = (log[FMAX * (R/L) * (C/L) * 2 * Pi * L2 * ((K-1)/K)2]) / logK

2. The line consists of resistor and capacitor segments only, unless a non-zero value is assigned to the ISPERL parameter. In this case, the capacitors are replaced with reverse-biased diodes, possessing the following characteristics:

• a zero-bias junction capacitance equivalent to the capacitance replaced
• a saturation current of ISPERL Amps/m of transmission line
• an optional series resistance equivalent to RSPERL Ohms/m of transmission line.

3. The link to the required model file (*.mdl) is specified on the Model Kind tab of the Sim Model dialog. The Model Name is used in the netlist to reference this file.
4. For model file parameters, where a parameter has an indicated default (as part of the SPICE model definition), that default will be used if no value is specifically entered. The default should be applicable to most simulations. Generally you do not need to change this value.
5. The simulation-ready URC transmission line component (URC) can be found in the Simulation Transmission Line integrated library (\Library\Simulation\Simulation Transmission Line.IntLib).

Examples

Consider the URC transmission line in the above image, with the following characteristics:

• Pin1 (node 1) is connected to net IN
• Pin2 (node to which capacitances of the RC line are connected) is connected to net GND
• Pin3 (node 2) is connected to net OUT
• Designator is URC1
• Length = 1
• No. Segments = 6
• The linked simulation model file is URC.mdl.

The entry in the SPICE netlist would be:

*Schematic Netlist:
UURC1 IN 0 OUT URC L=1 N=6
.
.
*Models and Subcircuit:
.MODEL URC URC()

In this case, there are no parameter values specified in the model file. The SPICE engine would therefore use the parameter values defined in the Sim Model dialog, along with the default values inherent to the model for all other parameters that are definable in the model file.