Sunday 19 August 2018

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Tcl/Tk Constellation Plot Display for ModelSim™

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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:

  • Introduction
    Document in PDF format, describing the add-in and explaining some of the specific techniques it uses.
     
  • ZIP archive
    All the files you need, stored as a ZIP archive for Windows.
     
  • .tar.gz archive
    All the files you need, stored as a compressed (gzipped) tar file for Unix.
     

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