Mixed Simulation References

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This reference area details the simulation models and circuit simulation analyses, including the Advanced SPICE options.

Analyses Reference

Main article: Analyses Reference

The Mixed Simulator supports a broad range of simulation analysis types, including:

The Advanced Options page of the dialog enables you to define advanced simulation options, including the values of SPICE variables, the integration method used by the Simulation Engine and the simulation reference net. In general, you should not have to change any of the parameters in this page of the dialog for accurate simulation. Only change these options if you understand SPICE simulation parameters. To learn more about the Advanced SPICE options, refer to the Advanced SPICE Options article.

Simulation Models

The Altium Designer-based Circuit Simulator is a true mixed-signal simulator, meaning that it can analyze circuits that include both analog and digital devices.

The Simulator uses an enhanced version of the event-driven XSpice, developed by the Georgia Tech Research Institute (GTRI), which itself is based on Berkeley's SPICE3 code. It is fully SPICE3f5 compatible, as well as providing support for a range of PSpice® device models.

Model Types

The models supported by the Simulator can be effectively grouped into the following categories:

SPICE3f5 Analog Models

Model References: SPICE3f5 Models

These are predefined analog device models that are built-in to SPICE. They cover the various common analog component types, such as resistors, capacitors and inductors, as well as voltage and current sources, transmission lines and switches. The five most common semiconductor devices are also modeled - diodes, BJTs, JFETs, MESFETs and MOSFETs.

A large number of model files (*.mdl) are also included, that define the behavior of specific instances of these devices.

PSpice Analog Models

These are predefined analog device models that are built-in to PSpice. To support these models, changes have been made to the general form for the corresponding SPICE3f5 device and/or additional parameter support has been added for use in a linked model file.

Note: These models are not listed separately in this reference. PSpice support information is included as part of the information for the relevant SPICE3f5 device model.

XSpice Analog Models

Model References: XSpice Models

These are predefined analog device code models that are built-in to XSpice. Code models allow the specification of complex, non-ideal device characteristics, without the need to develop long-winded sub-circuit definitions that can adversely affect Simulator speed performance. The supplied models cover special functions such as gain, hysteresis, voltage and current limiting and definitions of s-domain transfer functions.

The SPICE prefix for these models is A.

Sub-Circuit Models

Model References: Sub-Circuit Based Models

These are models for more complex devices, such as operational amplifiers, timers, crystals, etc, that have been described using the hierarchical sub-circuit syntax.

A sub-circuit consists of SPICE elements that are defined and referenced in a fashion similar to device models. There is no limit on the size or complexity of sub-circuits and sub-circuits can call other sub-circuits. Each sub-circuit is defined in a sub-circuit file (*.ckt).

The SPICE prefix for theses models is X.

Math Function Models

Model References: Math Function Models

Math functions allow the designer to perform behavioral modelling of the circuit. 

The SPICE prefix for theses models is X.

Digital Models

These are digital device models that have been created using the Digital SimCode™ language. This is a special descriptive language that allows digital devices to be simulated using an extended version of the event-driven XSpice. It is a form of the standard XSpice code model.

Source SimCode model definitions are stored in an ASCII text file (*.txt). Compiled SimCode models are stored in a compiled model file (*.scb). Multiple device models can be placed in the same file, with each reference by means of a special "func=" parameter.

The SPICE prefix for theses models is A.

Digital SimCode is a proprietary language - devices created with it are not compatible with other simulators, nor are digital components created for other simulators compatible with the Altium Designer-based mixed-signal Simulator.


For more detailed information concerning SPICE, PSpice and XSpice, consult the respective user manuals for each. The XSpice manual is particularly useful for learning about the syntax required for the Code Models added to XSpice by GTRI and extensions that have been made to SPICE3.

Many of the component libraries (*.IntLib) that come with the installation, feature simulation-ready devices. These devices have the necessary model or sub-circuit file included and linked to the schematic component. These are pure SPICE models for maximum compatibility with analog simulators.

There were no syntax changes made between SPICE3f3 and SPICE3f5. The manual for SPICE3f3 therefore describes the correct syntax for the netlist and models supported by the Altium Designer-based mixed-signal Simulator.

Component and Simulation Multipliers

When entering a value for a component or other simulation-related parameter, the value can be entered in one of the following formats:

  • As an integer value (e.g. 10)
  • As a floating point value (e.g. 3.142)
  • As an integer or floating point value followed by an integer exponent (e.g. 10E-2, 3.14E2)
  • As an integer or floating point value followed by a valid scale factor
  • With respect to the last format, the following is a list of valid scale factors (multipliers) that can be used:

Simulation Scale Factors

Scale Factor



10 12


10 9


10 6


10 3


25.4 -6


10 -3

u (or μ)

10 -6


10 -9


10 -12


10 -15


  1. Letters immediately following a value that are not valid scale factors will be ignored.
  2. Letters immediately following a valid scale factor are also ignored. They can be beneficial as a reference to measurement units used, when viewing the component on the schematic and the relevant parameter is made visible.
  3. The scale factor must immediately follow the value - spaces are not permitted.
  4. The scale factors may be entered in either lower or upper case, or a mixture thereof.

Example Scale Factors

  1. 10, 10V 10Volts and 10Hz all represent the same number, 10. The letters are ignored in all cases as none of them are valid scale factors.
  2. M, m, MA, MSec and MMhos all represent the same scale factor, 10-3. In each case, the letters after the first "m" are ignored.
  3. 1000, 1000.0, 1000Hz, 1e3, 1.0e3, 1KHz and 1K all represent the same number, 1000.


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