Unlike SPICE, which is designed mainly for analog simulation, mixed-mode
simulators such as Multisim and CircuitLogix include both analog and event-
driven digital simulation capabilities in the same executable. This means
that any simulation may contain components that are analog, event driven
(digital or sampled-data), or a combination of both. An entire mixed signal
analysis can be driven from one integrated schematic. All the digital models
in mixed-mode simulators provide accurate specification of propagation time
and rise/fall time delays.
The event driven algorithm provided by mixed-mode simulators is general
purpose and supports non-digital types of data. For example, elements can use
real or integer values to simulate DSP functions or sampled data filters.
Because the event driven algorithm is faster than the standard SPICE matrix
solution simulation time is greatly reduced for circuits that use event
driven models in place of analog models.
Mixed-mode simulation is handled on three levels; (a) with primitive digital
elements that use timing models and the built-in 12 or 16 state digital logic
simulator, (b) with subcircuit models that use the actual transistor topology
of the integrated circuit, and finally, (c) with In-line Boolean logic
expressions.
Exact representations are used mainly in the analysis of transmission line
and signal integrity problems where a close inspection of an IC’s I/O
characteristics is needed. Boolean logic expressions are delay-less functions
that are used to provide efficient logic signal processing in an analog
environment. These two modeling techniques use SPICE to solve a problem while
the third method, digital primitives, use mixed mode capability. Each of
these methods has its merits and target applications. In fact, many
simulations (particularly those which use A/D technology) call for the
combination of all three approaches. No one approach alone is sufficient.
Chuck said:
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simulator does mixed-mode (digital and analog). Have fun with your toy
simulator.
A real simulator? Spices are analog simulators by nature.
I'm having difficulty understanding why you would want to
throw digital in with an analog simulation.
Do tell!
-Chuck