Working with Simulation Results

When required analyses are configured and run, analysis results are written to a Simulation Data File (SDF), which is named after the project itself (<ProjectName>.sdf) and appears in the Projects panel under the Generated\Simulation Documents folder. The file automatically opened as a document tab – presented in the SimData editor. This feature-rich environment allows you to quickly and efficiently analyze simulation results, enabling you to assess, debug and ultimately emerge confident in the operation of your design. Note that although created, this file is initially unsaved.

Working with the List of Simulation Results

Performed simulation runs are displayed in the Results region of the Simulation Dashboard panel. The  button at the right of a specific result entry offers the following actions:

  • Show Results – reopen the results from that run. You can also double-click a result name to reopen it.
  • Load Profile – restore the analysis settings from that run in the corresponding region of the Simulation Dashboard panel's Analysis Setup & Run region.
  • Edit Title – rename the result entry. By default, a result is named after the analysis.
  • Edit Description – edit the description of the result entry. By default, a description reflects the key parameters of the run. You can also click the description field to edit it.
  • Delete – delete the result entry.

Use the Results region of the Simulation Dashboard panel to manage simulation results.
Use the Results region of the Simulation Dashboard panel to manage simulation results.

You also can toggle the lock icon (/) associated with a simulation result entry to preserve the results of that run, where a subsequent analysis run of that type will be renamed with an incremented number suffix. Simulation result locking allows you to accumulate the results from multiple runs of the same analysis type.

Charts, Plots and Waveforms

A Simulation Data File can essentially be broken down into three constituent parts:

  • Charts
  • Plots
  • Waveforms

A chart can be thought of as a 'page' in the SDF file. An SDF file can contain multiple charts, the content of each depending on the type of analysis being performed. A plot is an area used to display data graphically and can be used to display one or more waveforms. A chart can contain multiple plots. A waveform represents analysis data collected from a specific point or node in a design.

Understanding the different elements in the simulation results
Understanding the different elements in the simulation results

When running a simulation, a separate chart will be created for each analysis type. The chart for an analysis type is accessed by clicking on its named tab at the bottom of the design space. Quickly flick through multiple charts of analysis results using the + and - keys on the numeric keypad.

Accessing simulation analysis results. Click on the relevant tab to see the results for that analysis type.
Accessing simulation analysis results. Click on the relevant tab to see the results for that analysis type.

For analyses that result in waveform data, the number of plots contained in a chart will depend on the analysis type, the probes added to the schematics and the output expressions added when configuring the analysis type.

The charts created for certain simulation analysis types will not contain plots and/or waveforms. For example, the chart for an Operating Point analysis displays textual data. The chart for a Pole-Zero analysis contains a single plot, but graphical pole (X) and zero (0) entries rather than waveforms in the typical 'analog wave' sense.

Quick tips for working in the SimData editor:

  • A wave can be moved from one plot to another by clicking and holding the waveform name, then dragging it to a different plot.
  • To display an existing wave on a new, separate plot, double-click on the name, then select New Plot in the Plot Number drop-down in the Edit Waveform dialog.
  • To zoom in to examine an area of a plot, left-click-and-drag a rectangle to define the new view area. To restore the view, right-click and select Fit Document.
  • Double-click anywhere within a plot to open the Plot Options dialog, where you can configure the Title, Grid Lines, and Line Style.
  • Double-click on an axis to label and configure that axis.
  • Double-click on the chart title to open the Chart Options dialog, where you can name the chart and also configure which cursor measurements are displayed on that plot, if the cursors are currently enabled.
  • Select Tools » Document Options from the menu to open the Document Options dialog, where you can configure the colors, the visibility of various wave, chart and plot elements (including the data points), and define the FFT length.

Selecting a Waveform

Selection of a waveform within the design space is a case of clicking on the waveform's name. Once selected, the waveform will become bolder in color and have a dot to the left of its name. Filtering is applied, using the name of the waveform as the scope. All other waveforms in the active chart with different names will be masked (becoming dimmed).

  • If more than one waveform of the same name exists in the active chart, the non-selected instances will remain at full visibility.
  • Select multiple waveforms using the Shift+Click shortcut. This might be useful to compare some waveforms in a waveform-dense plot.

The extent of the masking can be controlled through the use of the Mask Level slider bar, accessed by clicking the Mask Level button located at the bottom-right of the design space.

Select a waveform by clicking on its name and set the mask level using the button and slider at the bottom right.
Select a waveform by clicking on its name and set the mask level using the button and slider at the bottom right.

To clear filtering and return to the full visibility of all plots, click the Clear button located at the bottom-right of the design space or use the Wave » Clear Filter command from the main menus (shortcuts: Esc, Shift+C). The previously selected waveform, on whose name the scope of the applied filter was based, will become deselected.

If a plot includes a considerable number of waveforms, the plot will include a scroll feature. Click on the available button(s) to scroll through all waveform names included in the plot.

Displaying Multi-pass Results

Temperature SweepParameter Sweep, and Monte Carlo analysis are simulation features that perform multiple passes of a basic analysis type (e.g., AC Sweep, Transient, etc), varying one or more circuit parameters with each pass. When the results are displayed within the SimData editor, the associated plot contains waveforms for multiple passes, and each pass is identified by adding a letter and a number after the waveform name (e.g., v(Output) p1v(Output) p2, etc.). The letter is used to signify the type of multi-pass analysis:

  • t – Temperature Sweep
  • p – Parameter Sweep
  • m – Monte Carlo

The number signifies the actual pass.

Example results of a Parameter Sweep analysis
Example results of a Parameter Sweep analysis

As you click on the waveform name, information on the parameter(s) used in that particular pass will appear underneath the plot and in the Status bar. Also, the other waveforms corresponding to the same parameter values are highlighted when the Highlight Similar Waves option is enabled in the Document Options dialog (Tools » Document Options).

Click a waveform for a specific pass to see its parameters and highlight other waveforms related to the same pass.
Click a waveform for a specific pass to see its parameters and highlight other waveforms related to the same pass.

Controlling the Number of Visible Plots

When analysis results are first written to an SDF file, they are, by default, displayed in an optimum way – displaying between one and four plots in view at a time, depending on the number of plots resulting from the analysis. For example, if there are three plots, the chart will be configured automatically to display all three plots in view. If there were six plots, the chart would be automatically configured to display four plots in view at a time, and so on. You can change how many plots are 'visible' by configuring the Number of Plots Visible option in the Document Options dialog accessed for the active SDF file by choosing Tools » Document Options from the main menus.

The settings defined in the Document Options dialog can be applied to the active chart only, all charts in the current SDF file, and/or saved as the default options – which will be applied to all subsequently generated charts. Use the drop-down at the bottom left of the dialog to choose a desired option.

Select the required Number of Plots Visible in the Document Options dialog.
Select the required Number of Plots Visible in the Document Options dialog.

By setting the number of plots visible to All, you will typically be able to see all plots at once within the design space (dependent, of course, on the number of plots resulting from the analysis). This is considered to be a 'draft mode' – providing a quick overview of the generated waveforms.

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When you want to analyze the waveforms in more detail, you should move from viewing all plots, to a specific number of them. The lower the number of plots visible in the design space at any one time, the easier it will be to concentrate on a particular waveform and take measurements from it. If you want to take advantage of resizing features (X- and/ or Y-axes), addition of Y-axes and plot labeling, you will need to set the Number of Plots Visible option to anything but All.

Rearranging Plots and Waveforms

You can change the order in which plots appear in a chart by clicking and dragging. First, ensure that the plot you wish to move is made active in the design space. When the Number of Plots Visible is set to All, the active plot is distinguished by a solid line around its waveform name section; if the Number of Plots Visible is set to 2, 3, or 4, the active plot is distinguished by an arrow at the left-hand side of its display area. Then click inside the waveform name area (away from the name itself) and drag up or down as required. A line will appear to indicate under which plot the plot you are moving will be placed if you release the mouse button.

Just as plots can be moved, waveforms themselves can be moved between plots. Click on a waveform name and drag it to the required destination plot. An arrow will appear at the top of the Y-axis for the recipient plot. Movement can be performed irrespective of the number of visible plots.

A waveform can also be moved to a new plot by double-clicking on the waveform's name, then selecting New Plot in the Plot Number drop-down in the Edit Waveform dialog that opens. After doing this, you may need to change the number of visible plots, this is done in the Document Options dialog (Tools » Document Options).

Move a waveform to a new plot using the Edit Waveform dialog.
Move a waveform to a new plot using the Edit Waveform dialog.

The video below demonstrates the process of rearranging plots and waveforms.

Demonstration of the plot and waveform rearrangement techniques.

  • Multiple selected waveforms (selected in the same or different plots using the Shift+Click shortcut) can also be moved to another plot using drag-and-drop.
  • You may need to adjust the Y-axis after the move to better 'fit' the waveforms. This is especially true if the destination waveform is larger in amplitude than the waveform in the target plot. For more information on adjustment of plot axes, see the Changing the Axis section.

Magnifying the Data

You can change the magnification of the active plot, allowing you to zoom in or out when analyzing waveform data. Use the dedicated Zoom In and Zoom Out commands from the View main menu to zoom in or zoom out, respectively. Alternatively, click and drag a selection square about a point of interest to magnify (zoom in) to that point.

When changing the magnification of the data in one plot, the other plots will not be changed. Disable the Zoom Plots Separately option in the Document Options dialog to apply the same level of magnification to all plots when changing the magnification of the data in one plot.

  • To zoom relative to the mouse pointer position using the Zoom In and Zoom Out commands, position the pointer and launch the command using its keyboard shortcut – PgUp for zoom-in and PgDn for zoom-out.
  • Use the Z keyboard shortcut to access a pop-up menu of zoom commands:
    • Zoom All – zoom to all waveforms in the current chart in their entirety.
    • Zoom In – bring the waveform(s) closer to you (zoom in) relative to the center positions of each associated wave plot in the active chart.
    • Zoom Out – move the waveform(s) away from you (zoom out) relative to the center positions of each associated wave plot in the chart.

To return to the initial display of the waveforms (non-magnified), run the Fit Document command from the main View menu or from the design space right-click menu (shortcut: Ctrl+PgDn).

The video below demonstrates the process of magnifying the simulation result data.

Demonstration of the magnifying data techniques.

Defining Multiple Y-axes for a Plot

There may be times where a single Y-axis will just not work. For example, you may be wanting to contrast current and voltage signals in a common plot. The voltage signal might run to 5V, whereas the current signal may be in the order of milliamps or microamps. To make the waveforms 'readable' the SimData editor provides for the use of additional Y-axes.

Consider the waveforms shown in the image below. One shows the input voltage and the other shows the current through a resistor. If the current waveform is now moved into the same plot as the voltage waveform, you can see that the current waveform is basically lost when scaled using the existing Y-axis for the plot. A better approach is to define a new Y-axis, giving the result shown below.

A new Y-axis can be added for the current waveform in one of the following ways:

  • Right-click on its name, choose Edit Wave, and in the Edit Waveform dialog that appears, select New Axis from the Axis Number drop-down.


    Set a new Y-axis for a waveform using the Edit Waveform dialog.
  • Add a new Y-axis (Plot » Add Y Axis), then drag the current waveform onto the axis to create association.

The new (automatically scaled) Y-axis for the waveform will be added to the left of the existing Y-axis. The result is easily readable waveforms in a single plot.

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To remove a Y-axis from a plot that has multiple Y-axes defined for it, click on the axis to select it and run the Plot » Remove Y Axis command. Alternatively, right-click on the axis and choose Delete Axis from the context menu.

Deleting a Y-axis will also delete the waveform associated to it. Of course, the waveform can always be added back into a plot from the Source Data region of the Sim Data panel. If you want to remove the axis without removing the waveform, however, you need to disassociate it from the axis. Click on the waveform's name and drag it onto the Y-axis that will remain. You can then go ahead and safely remove the redundant Y-axis.

Displaying Data Points

If you are unsure about the accuracy of the waveforms – perhaps they look sharp and jagged instead of smooth and curved – you can enable the display of data points, to check if the results have been calculated often enough.

To display these points, enable the Show Data Points option in the Document Options dialog. A small circle will be displayed at each point along the wave at which data was calculated.

Use the Show Data Points option to visualize the accuracy of the waveforms.
Use the Show Data Points option to visualize the accuracy of the waveforms.

Fast Fourier Transform

By using the Chart » Create FFT Chart command, you can quickly perform a Fast Fourier Transform on each waveform in the active chart. The results are stored in, and displayed on, a new chart, which is named using the format <SourceChartName>_FFT and added to the right of the existing charts in the SDF file.

Set the FFT Length in the Document Options dialog (Tools » Document Options). By default, the length is 128.

Use the Create FFT Chart command to perform a Fast Fourier Transform.
Use the Create FFT Chart command to perform a Fast Fourier Transform.

Other Features for Chart, Plot and Waveform Management

Refer to the sections below to learn about other features for chart, plot and waveform management.

Working with Textual Data

The charts created for Operating Point and Transfer Function analysis types will not contain plots and/or waveforms – these charts display textual data. In this case, a 'waveform' represents a single calculated value. Add the required values to the chart by selecting the corresponding entry in the Source Data list in the Sim Data panel and clicking the Add Wave to Plot button.

An example of adding a calculated value of a Transient Function analysis.
An example of adding a calculated value of a Transient Function analysis.

Textual information can be copied to the clipboard using the Tools » Copy to Clipboard as Text command from the main menus.

Working with Digital Plots

Digital plots represent the logical level in a digital node: 0 or 1. An example of a digital plot is shown below.

An example of a digital plot
An example of a digital plot

Digital waveforms can also show the undefined and high-impedance states by using two- and three-line wave sections, respectively.

Undefined (first image) and high-impedance (second image) states shown on a digital plot. 
Undefined (first image) and high-impedance (second image) states shown on a digital plot.

Note that measurement cursors represent undefined and high-impedance states as 'X' and 'Z', respectively.

Representation of undefined and high-impedance states by measurement cursors.

Representation of undefined and high-impedance states by measurement cursors.

  • Digital plots have no Y-axis since only digital levels are shown for digital waves. Also, note that digital and analog waves cannot be mixed in a single plot.
  • Boolean functions can be applied to digital waves. The resulting waves will still be digital, i.e. they will be shown on a digital plot. Other operations will convert the resulting wave into an analog wave.

Working with Measurement Results

The result data of measurements are displayed on the Measurements tab of the Sim Data panel when exploring the simulation result document.

There are a number of features to assist you in analyzing the simulation measurement results. The features include:

  • Select a measurement value and click the Show on chart button to display the measurement cursors on the plot highlighting the region for which the measurement has been calculated. Learn more about Cursors-based Measurements.

    Use the Show on chart button to visualize the measurement.
    Use the Show on chart button to visualize the measurement.

  • Click the Add button to access the Add Waves to Plot dialog where a new waveform and measurements for it can be defined.
  • Click the  button to access the Edit Waveform dialog where an existing waveform and the currently defined measurement can be edited; no need to return to the Simulation Dashboard panel.

When the simulation result document includes waveforms for multiple passes of the analysis (e.g, when performing a temperature sweep or Monte Carlo analysis), there will be a measurement value for each waveform. In this case, a table of measurements will be presented on the Measurements tab of the Sim Data panel, and the following features are accessible:

  • Measurement statistics are calculated automatically and displayed in the lower region of the Sim Data panel.
  • A full table of the measurement results can be displayed by clicking the Expand the table control in the Sim Data panel. The table will be shown in the Measurement Table chart. The data in the table can be selected and copied (e.g., to paste it to a spreadsheet).
  • Generate a plot using the Plot button. For example, if a parametric sweep has been performed, you can create a plot of the measurement values against the swept parameter. The plot will be added to the Measurement Plot chart.
  • Visualize the distribution of data by generating a histogram using the Histogram button. The histogram will be added to the Measurement Histogram chart.
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Taking Direct Measurements

The SimData editor provides features for obtaining measurement information directly within the design space. Base measurements are automatically presented for a selected waveform. If you want to take more precise measurements, dedicated measurement cursors are available – enabling you to take measurements in a more interactive way.

Measurements for a Selected Waveform

General measurements for a selected waveform are presented in the Waveform Measurements region of the Sim Data panel.

General measurements for a selected waveform.
General measurements for a selected waveform.

Data is calculated from the waveform itself and does not involve the measurement cursors in any way. The following data is calculated:

Rise Time The time taken by the signal to change from 10% to 90% of the difference between Top Line and Base Line values. Measurement data is only available when the selected signal is power-based (mixed-signal simulation) or is a resultant waveform of a signal integrity analysis.
Fall Time The time taken by the signal to change from 90% to 10% of the difference between Top Line and Base Line values. Measurement data is only available when the selected signal is power-based (mixed-signal simulation) or is a resultant waveform of a signal integrity analysis.
Min The minimum value reached by the waveform. The X-axis value at which this point occurs is also displayed.
Max The maximum value reached by the waveform. The X-axis value at which this point occurs is also displayed.
Base Line The steady state value for the low level of the signal waveform. This value is most noticeable, graphically, for a signal integrity-based analysis waveform, where ringing of the signal occurs about this base line value (undershoot).
Top Line The steady state value for the high level of the signal waveform. This value is most noticeable, graphically, for a signal integrity-based analysis waveform, where ringing of the signal occurs about this top line value (overshoot).

Cursor-based Measurements

Precise data measurements can be taken by using the SimData editor's dedicated measurement cursors. Two cursors are available – Cursor A and Cursor B – which can be added to the same or different waveforms in the design space.

A cursor (A or B) can only be used once in the active chart. If you choose to assign a cursor to a waveform and another waveform is already using that cursor, the cursor will be reassigned to the new one.

Addition of a measurement cursor can be made in one of two ways:

  • Select the waveform and use the Wave » Cursor A or Wave » Cursor B command.
  • Right-click on the waveform's name and choose Cursor A or Cursor B from the context menu.

An added cursor will appear as a tab at the top of the plot in which the waveform resides, and will assume the same color as the waveform to which it is assigned. Crosshairs appear within the plot, intersecting the waveform. Move the cursor by clicking and dragging its tab.

Cursor's intersection and tab
Cursor's intersection and tab

As you move the mouse pointer over the area of a plot, the XY value pair is shown at the far left of the Status bar.

Measurement data is available in the Measurement Cursors region of the Sim Data panel. You can also enable display of measurement data within the design space. This is done from the Cursors tab of the Chart Options dialog (Chart » Chart Options).

The Cursors tab of the Chart Options dialog
The Cursors tab of the Chart Options dialog

The availability of cursor measurements – both in the design space and on the Sim Data panel – depends on how the measurement cursors have been assigned:

  • If a single cursor is being used, you can read just the XY values of the cursors' intersect point.
  • If the two cursors have been added, to different waveforms, you can measure:
    • XY values
    • B-A
  • If the two cursors have been added, to the same waveform, you can measure:
    • XY values
    • B-A
    • Minimum A..B
    • Maximum A..B
    • Average A..B
    • AC RMS A..B
    • RMS A..B
    • Frequency A..B
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Select the cursor by clicking on its tab to gain access to a range of commands on the main Wave menu that operate on the cursor. You can move it to the maximum or minimum point on the waveform or quickly jump to the next/previous peak/trough.

To remove a cursor, use the Wave » Cursor A or Wave » Cursor B command from the main menu or right-click the cursor tab and select the Cursor Off command from the context menu.

Cross Probing to the Schematic

The SimData editor offers the ability to cross-probe from the selected waveform to the corresponding analysis node in the circuit from which the results for that waveform were captured. 

To use this feature, right-click on the name of a waveform in the design space and choose Cross Probe to Schematic from the pop-up menu that appears. The source schematic document will be made active and the corresponding node highlighted – in accordance with the Highlight Methods defined on the System – Navigation page of the Preferences dialog.

You can only cross-probe from waveforms for which data was captured through analysis of the schematic circuit. If you have edited a source waveform by applying a mathematical expression to it, or if you have created a new waveform, you will not be able to cross-probe.
Note

The features available depend on your level of Altium Designer Software Subscription.

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