Tcl/Tk Constellation Plot Display for ModelSim™
Tk Add-ins for ModelSim
Mentor's ModelSim HDL simulator has a GUI that is largely written in Tk. The ModelSim command console runs a Tcl/Tk shell, so that you can run your own Tcl scripts from within the simulator. It's also possible to modify the simulator's GUI using Tk.
Constellation diagrams
Many communications-related functions involve modulation of a carrier signal both in phase and in amplitude.
After demodulation, the signal is usually represented as an in-phase and a quadrature component, representing the amplitude of cosine and sine components respectively.
It is very helpful to view these signals on a so-called "constellation" diagram, also known as a polar plot or Argand diagram - a 2-dimensional representation with in-phase on the X axis and quadrature on the Y axis.
At any instant, the signal's two values can be represented by a point on this X/Y plot.
In a digital comms system, the in-phase and quadrature components are probably represented in multi-bit digital values.
ModelSim's waveform display can easily display each of these values in a convenient analog format, giving an oscilloscope-like display.
Our constellation plot add-in is an example of how to add custom GUI functionality to ModelSim, providing a display that's not possible in the standard simulator product.
Download the constellation plot add-in
Right-click on these links to download:
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Introduction
Document in PDF format, describing the add-in and explaining some of the specific techniques it uses.
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ZIP archive
All the files you need, stored as a ZIP archive for Windows.
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.tar.Z archive
All the files you need, stored as a compressed tar file for Unix.