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VHDL Modeling of Transmission Line Effects in Hardware Designs

IP.com Disclosure Number: IPCOM000102643D
Original Publication Date: 1990-Dec-01
Included in the Prior Art Database: 2005-Mar-17
Document File: 9 page(s) / 282K

Publishing Venue

IBM

Related People

Stanisic, BR: AUTHOR

Abstract

Disclosed is a novel approach using the VHSIC Hardware Description Language (VHDL) to model the digital-transmission line interaction. The details and novel application of the general simulation model structure to transmission lines constitutes the invention.

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VHDL Modeling of Transmission Line Effects in Hardware Designs

       Disclosed is a novel approach using the VHSIC Hardware
Description Language (VHDL) to model the digital-transmission line
interaction.  The details and novel application of the general
simulation model structure to transmission lines constitutes the
invention.

      This model structure is based on the general model structure
described by (1).  The transmission line data structure which
supports the behavioral models is coded in the 7.2 version of VHDL
(2) and is shown in Fig. 1.

      The constants G_MIN, G_MAX, R_MIN, and R_MAX are used by the
transmission line behaviors to bound the conductance and resistance
specified by the user in generics.  Also note that the units of these
bounded values are in Kohms and milliohms.  This establishes the
consistent set of units volts, mA and Kohms.

      The transmission line node, TLINE_NODE, is defined as a record
consisting of four floating-point fields.  The first, VOLT, stores
the total voltage on the node.  The second, G0, contains the total
conductance of all elements connected to the node.  The remaining
fields, VOLT_FE and CUR_FE, hold the far-end total voltage and branch
current for nodes with a "total" driver connection (explained later).
Finally, all elements are of type BRF_REAL  which is defined in the
summing resolution function package of Fig. 2.

      Thus, all signal elements of type BRF_REAL are summed when they
are dotted.

      The basic behavioral models required to simulate transmission
line effects are the transmission line, the driver, and the receiver.

      The transmission line is the most important element of the
system.  It transfers information between nodes, calculates
reflections, and forms the dominant characteristic of the network.
The algorithm for this behavioral is shown in Fig. 3.

      When an event occurs at an end of the transmission line (NODE1
in this case) its volt field contains the total voltage on the node.
This total voltage, less the amount internally incident at NODE1,
represents the voltage internally reflected and entering the line at
NODE1.  This combined amount, C, is incident at the far end of the
line after the time-of-flight and stored in INT2.  Transmitted to the
NODE2 volt field is this incident voltage multiplied by the
transmission coefficient (1 + K).  Other quantities are updated based
on these transmitted and internally incident voltages.

      The total current entering the line at NODE1 is simply the
total incident voltage traveling toward NODE2 less the internally
incident voltage at NODE1 divided by the characteristic resistance
r0.  This result is stored in BR1. The far end quantities cur_fe and
volt_fe store the total voltage and branch current present at the far
end when the transmitted voltage was determined.  These quantities
are used when nonlinear elements are connected to the line.  The VHDL
transm...