Content

This page contains some information about the modeling and specification of hybrid and mixed analog/digital (mixed-signal) systems.

1. What is a hybrid/mixed or analog/digital System?
2. Links to other pages
3. Local stuff: VHDL-AMS parser in java, some KANDIS/KIR-tools

What is a hybrid/mixed or an analog/digital System?

The word "hybrid" is often used as a synonymous word for heterogeneous. We use it more specific for systems which are described using different computational models:

• Differential Equations (Differential Equations Specified Systems, DESS)
• Difference equations, Automata (Discrete Time Specified Systems, DTS)
• Processes (Discrete Event Specified Systems, DEVS)

Hybrid systems can be found in many domains: Digital controllers, which are embedded in continuous-time systemshybrid systems are as well hybrid systems as mixed analog/digital circuits ("mixed-signal ASICS").

Many modeling languages - most notably VHDL-AMS (IEEE 1076.1) - support the description of mixed analog/digital or hybrid systems.

For graph-based description of hybrid systems, we can distinguish three approaches:

1. The control-flow oriented approach (Hybrid Automata, Hybrid Petri-Nets, Hybrid State-Charts): Discrete states are modeled by vertices of a graph, while continuous states are modeled by (real-numbered) variables. Each vertice has a set of differential equations which are valid, when the control-flow is in this vertice. Very formal approach, which is very nice for verification.
2. The data-flow oriented approach (Block-Diagrams, KIR/Hybrid Data-Flow Graphs): Block-Diagrams are an informalway to describe signal-flow and structure of a system. KIR-Graphsarea more formal way: They are an extension of Data-Flow Graphs.Eachnode has its own firing rule: continuous-time, discrete-timeor discrete-event. This model can be used as intermediate representationfor optimizations, since it is completely graph-based and many well-knowncompiler optimizations can be applied.
3. The homogeneous discrete-time approach (z-transform): Continuous-time parts are translated into discrete-time approximations. Can be used, when embedded controllers are designed.

Further informations about hybrid and mixed analog/digital systems

Articles, Standardisation, Public Domain

Thomas Henzingers (and other) papers about hybrid Automata

Homepage of IEEE DASC 1076.1 (1076.1)

Papers about KIR and KANDIS

If you know papers about hybrid and mixed analog/digital systems, which are available in the web, please EMail me, I will add them to the list above.

Commercial Products

VHDL-AMS Simulators:

ASIC Foundries for mixed-signal technologies:

Local stuff: VHDL-AMS (IEEE 1076.1) Frontend, VHDL-AMS Examples.

The parser covers the complete IEEE 1076 - Standard including the extensions proposed as IEEE 1076.1. I implemented it using the JavaCC Compiler-Compiler from SUN. Currently, only syntax check works.

Download the VHDL-AMSParser Class(.tgz)

Download Sourcecode (.zip)
If you want to use it for other than evaluation purposes, send an email to me.

As an example for the expressive power of VHDL-AMS most notably on behavioral level, take a look at a small example, a dynamic compressor specified in VHDL-AMS:
compressor.vhdl                            

Legal stuff:
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