Spectrum Software
Industrial Strength Simulation




Spectrum Software has released Micro-Cap 11, the eleventh generation of our SPICE circuit simulator.

For users of previous Micro-Cap versions, check out the new features available in the latest version. For those of you who are new to Micro-Cap, take our features tour to see what Micro-Cap has to offer.




Using the Waveform Buffer


Micro-Cap 9 provides a feature that can easily display waveforms within an analysis plot that have been saved from previous runs or even from simulations of other circuits. The Waveform Buffer provides the capability to store and retrieve waveforms. The buffer can be used with waveforms created in transient, AC, DC, or distortion analysis.

The Waveform Buffer is available under the Scope menu when in an analysis. The dialog box appears as below:

Waveform Buffer dialog box

The list displays the waveform labels, the circuit name from which they came, and the date and time they were stored in the Waveform Buffer. A check box adjacent to the label protects the waveform from deletion. The plot on the right provides a view of the selected waveform. Above the plot is a field to edit the waveform label. The other interesting functions of the dialog box are as follows:

Plot Now: This immediately adds the selected waveforms to the analysis plot and places entries into the analysis limits so the waveforms are displayed in future runs also.

Add to Limits: This places entries in the analysis limits for all selected waveforms so that they will be displayed the next time the simulation is run.

Delete: This deletes the selected waveforms whose check boxes adjacent to the waveform name have not been enabled.

Delete All: This deletes all waveforms whose check boxes adjacent to the waveform name have not been enabled.

Auto Save: When enabled, the auto save will save all waveforms from every analysis run into the buffer. As you can imagine, this will use up space after a while so the Allow Meg field specifies how much memory is available to the Waveform Buffer. Once this limit is reached, waveforms will be deleted starting with the oldest to make room for the newer waveforms. Again, the check box adjacent to the curve name will protect the waveform from being deleted if it is enabled.

Waveform Buffer Examples
The waveform buffer is simple to use. For the following example, the UA709 amplifier has been set up to operate with a gain of 100. A transient simulation was then run. Once the simulation is finished, right clicking on a waveform name invokes the popup menu shown below.

Waveform name right click menu

Two of the entries in the popup menu are applicable to the Waveform Buffer. Add to Buffer will store the selected waveform in the Waveform Buffer. Retain stores the selected waveform in the Waveform Buffer and also adds an entry in the analysis limits so that the saved waveform will be plotted in future runs. The Add to Buffer and Retain capabilities are also available under the Scope / Waveform Buffer menu. For this example, the Retain command was selected from the menu for the V(Out) waveform. The following dialog box is then invoked.

Waveform Buffer Add dialog box

This dialog box lets you edit the label for how the waveform will be listed in the Waveform Buffer. If the simulation has produced multiple runs such as with Stepping, you can select which branch will be stored. In this instance, the waveform label is defined as V(Out) vs. T. Clicking OK saves the waveform in the buffer. Since Retain was selected, the following entry was also made in the analysis limits as a new Y Expression to be plotted:

Buffer("V(Out) vs. T")

This expression has been assigned to the same Plot Group as the original V(Out) waveform. Now when the transient analysis is run again, the V(Out) vs. T waveform will be retrieved from the Waveform Buffer and plotted so it can be compared to subsequent plots of V(Out).

In the schematic, the feedback resistor has been modified from 100kohm to 50kohm so that the opamp now produces a gain of 50. The resultant transient simulation below displays the modified V(Out) waveform versus the retained V(Out) waveform. Note that when a waveform is retrieved from the Waveform Buffer, its waveform expression in the plot is enclosed with quotation marks. It will now be easy to compare any future output waveform versus the original output waveform.

The retained V(Out) waveform

Since the V(Out) vs. T waveform is stored in the Waveform Buffer, it can be imported into any transient, AC, DC, or distortion analysis for any circuit.

For a second example of using the Waveform Buffer, the same circuit with the UA709 amplifier will be used. The feedback resistor has been restored to its original 100kohm value. In this case, an AC simulation is run, and the expression dB(V(Out)) is plotted. Once the AC analysis is finished, the Waveform Buffer is invoked. As shown below, the V(Out) vs. T waveform previously stored from the transient analysis is now available. This waveform is selected and the Plot Now button clicked. The transient output voltage will then be plotted alongside the AC results as shown in the following simulation.

Waveform Buffer dialog box with V(Out) vs T

Plotting V(Out) vs T in AC analysis

When plotting a waveform from the buffer, an entry is always made in the analysis limits so that the waveform will automatically be displayed in future runs. To delete this waveform for any subsequent runs, simply delete that entry within the analysis limits.

When a waveform is stored in the buffer, the color, width, pattern, and style of that waveform are also stored. These will be the default entries for the waveform when it is initially retrieved from the buffer. Once retrieved, the waveform properties can be modified through the analysis limits or the Properties dialog box like any other waveform in the plot.

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