Parameter Sweep

Multisim Help


Edition Date: February 2017
Part Number: 375482B-01
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Parameter Sweep analysis allows you to run a series of underlying analyses, such as DC or Transient, as one or more parameters in the circuit is varied for each analysis run. This analysis is more generalized than DC Sweep.

You can sweep circuit parameters, device parameters, and model parameters.

Circuit parameters

Circuit parameters are user-defined parameters that can be assigned to component parameters. By sweeping a circuit parameter, you can indirectly sweep any component parameters which use this circuit parameter. Select View»Circuit Parameters to display the Circuit Parameters window. Refer to the Circuit Parameters topic for more information.

It is recommended that you use circuit parameters for most sweep applications. There are two advantages to using circuit parameters over device and model parameters:

  • Device/model parameters operate in the netlist context and do not provide a direct correlation to what you see on the schematic. Circuit parameters are assigned to component parameters directly in the property dialogs. It is easier to directly determine their effect on the simulation.
  • You can sweep parameters that you cannot sweep using device/model parameters. For instance, you cannot sweep the peak voltage of an AC source using device/model parameters. And you cannot sweep (in any intuitive way) parameters of components that use macro-models such as transformers or PWMs. With circuit parameters, you simply enter a circuit parameter as the value of the component parameter and then sweep the circuit parameter.

Device and Model parameters

Device and model parameters are pre-defined by the simulator and are associated with SPICE devices within the netlist. They may not have an obvious association to components in the schematic because models of components often contain several devices.

A device parameter, also known as an instance parameter, is a parameter found in the netlist in the instance definition line of a particular SPICE device. For example, the SPICE resistor device has a parameter called resistance, whose value is specified as an instance parameter directly after the node connections, as follows:

Rxx node+ node- resistance_value

A model parameter is a parameter found in the netlist in the .model statement of a particular SPICE device. For example, the SPICE diode device has a model parameter called cjo, specified in the .model statement as follows:

.model 1n4148 d(cjo=value)

Parameters for semiconductor devices are typically found in the .model line.

Typically, models of basic Multisim components like resistors and capacitors consist of a single SPICE device. Sweeping the resistance device parameter, sweeps the resistance of the resistor component.

However, more advanced components such as opamps, power MOSFETs, and even some diodes, use macro-models which use many SPICE devices to synthesize overall model behavior. In these cases, the devices do not have a direct correspondence to the model of the component or the component parameters shown in the property dialog boxes. Sweeping parameters of these internal devices might be completely baseless. Therefore, sweeping device/model parameters should be reserved for cases when it is clear to the user which property of a component's model is affected by the device/model parameter.

Sample files for use with analyses are installed at C:\Users\Public\Documents\National Instruments\Circuit Design Suite <version>\samples\Analyses\.

Analysis Parameters

The Analysis parameters tab contains the following:

  Parameter  
Description
Sweep parameters
Sweep parameter—Choose Device parameter, Model parameter or Circuit parameter. Some components may not have both device and model parameters.
Device type—The type of device to sweep. This is the name of the SPICE device. This is not applicable to circuit parameters.
Name—The component to sweep. If sweeping a model parameter, this is the model name. If sweeping a device parameter, this is the RefDes. This is not applicable to circuit parameters.
Parameter—The name of the parameter to be swept.
Present value—Preview of the present value of the parameter. This will be overridden by the analysis.
Description—Describes the selected Parameter. This is for information only and is not applicable to circuit parameters.
Points to sweep
Sweep variation type—Sets how to calculate the interval between the stop and start values. Choose Decade, Linear, Octave or List.
Decade
Start—The start value of the sweep.
Stop—The stop value of the sweep.
Number of points per decade—The number of points in a decade. The number of decades is the number of times the start value can be multiplied by ten before reaching the end value.
Linear
Start—The start value of the sweep.
Stop—The stop value of the sweep.
Increment—The size of the step increment.
Number of points and increment are related through:
Number of points = (Start-Stop)/Increment
Octave
Start—The start value of the sweep.
Stop—The stop value of the sweep.
Numbe of points per octave—The number of points in an octave. The number of octaves is the number of times the start value can be doubled before reaching the end value.
List
Value list—A list of values to sweep. Values must be separated by spaces, commas or semicolons.
More options
Analysis to sweep—This is the underlying analysis that is run for each value of the swept parameter. Choose DC Operating Point, AC Sweep, Single Frequency AC, Transient or Nested Sweep.
Display results on a graph—Appears when DC Operating Point or Single Frequency AC is selected in the Analysis to sweep drop-down list. Select to display the analysis results on a graph.
Display results in a table—Appears when DC Operating Point or Single Frequency AC is selected in the Analysis to sweep drop-down list. Select to display the analysis results in a table.
Group all traces on one plot—Select to place all traces on the same plot in the Grapher. Otherwise, the outputs for each sweep appear on a new graph page.
Edit analysis—Click to edit parameters of the chosen analysis. For Nested Sweep , refer to the Nested Sweep Analyses section.

 

Related Information

Setting Up and Running an Analysis

Output Tab

Analysis Options Tab

Summary Tab

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