Simulator Reference: Lossy Transmission Line

Netlist Entry

Oxxxx p1 n1 p2 n2 modelname [IC=v1,i1,v2,i2]

p1	Positive input port 1
n1	Negative input port 1
p2	Positive input port 2
n2	Negative input port 2
modelname	Name of model defined in a .MODEL statement. Must begin with a letter but can contain any character except whitespace and period '.'.
v1,i1,v2,i2	Initial conditions for voltage at port 1, current at port 1, voltage at port 2 and current at port 2 respectively. These only have an effect if the UIC parameter is specified on the .TRAN statement.

Model Syntax

.model modelname LTRA ( parameters )

Model Parameters

Name	Description	Units	Default
R	Resistance/unit length	???MATH???\Omega???MATH???/unit length	0.0
L	Inductance/unit length	Henrys/unit length	0.0
G	Conductance/unit length	Siemens(mhos)/unit length	0.0
C	Capacitance/unit length	Farads/unit length	0.0
LEN	Length		Required
REL	Relative rate of change of derivative for breakpoint	1.0
ABS	Absolute rate of change of derivative for breakpoint	1.0

The parameters REL and ABS control the way the line is simulated rather than its electrical characteristics. More accurate results (at the expense of simulation time) can be obtained by using lower values.

Notes

The uniform RLC/RC/LC/RG transmission line model (LTRA) models a uniform constant-parameter distributed transmission line. The LC case may also be modelled using the lossless transmission line model. The operation of the lossy transmission line model is based on the convolution of the transmission line's impulse responses with its inputs.

The following types of lines have been implemented:

RLC	Transmission line with series loss only
RC	Uniform RC line
LC	Lossless line
RG	Distributed series resistance and parallel conductance

All other combinations will lead to an error.

REL and ABS are model parameters that control the setting of breakpoints. A breakpoint is a point in time when an analysis is unconditionally performed. The more there are the more accurate the result but the longer it will take to arrive. Reducing REL and/or ABS will yield greater precision.

Example

The above could represent a 10 metre length of RG58 cable. The parameters would be described in a .model statement e.g.

.model RG58_10m LTRA(R=0.1 C=100p L=250n LEN=10)

Subcircuit-based RLGC Model

A subcircuit-based lossy transmission line model is also provided in the model library and accessible in the schematic editor from the menu system. The sub-circuit model uses the Laplace Transfer Function Convolution Implementation device as its base. The sub-circuit model is faster, more accurate and also supports both shunt and series losses. The subcircuit model may be entered using

Xxxx p1 n1 p2 n2 LOSSY_LINE params:
+ C=cap-per-unit-length
+ L=ind-per-unit-length
+ G=shunt-conductance-per-unit-length
+ R=series-r-per-unit-length LENGTH=length