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.




Dynamic Analysis Mode


This article explains the dynamic analysis mode and how to use it.

How it works: In dynamic analysis mode you usually employ a screen split between two windows. One window shows the schematic or SPICE netlist (Micro-Cap can simulate either one). The other window shows the analysis plot. When you make a change to the schematic, the analysis is re-run and the analysis plot is updated.

Activation: Dynamic analysis is always active.

We'll use this circuit as a vehicle to explain how the mode is used.


This circuit is a microphone preamp. Press F2 and its AC analysis looks like this:

Amplifier AC Analysis

Notice that the Accumulate Plots option is enabled. This accumulates and displays all plots including the original and any changes made during the analysis session. Now click in the schematic on R3 and press the Up Arrow key. You should get this picture.

AC Analysis for Two R3 Values

Press the Up Arrow key twice more and you get this picture.

AC Analysis for Four R3 Values

For each change made in the schematic you get one more plot. In some instances, you may find it is easier to avoid the Accumulate Plots option. The simulation run is often so fast that you can alternately use the up and down arrow keys and get an intuitive feel for the effect a particular parameter has. For instance, in this example, the resistor R2 affects both gain and bandwidth. The capacitor C2 affects the low frequency cutoff and the capacitor C3 affects the upper frequency bandwidth.

Here is the effect of doubling C2.

Doubling C2

Here is the effect of doubling C3.

Doubling C3

All of this you could do by stepping the component values and you probably should do it that way after you understand the nuances of your circuit. Until then it's nice to develop an intuitive understanding of the circuit function by seeing the effect that small changes have on the circuit behavior.

Note that the changes are not limited to using the arrow keys. You can double-click on a component and make any changes you want.

As with any schematic change, Undo (CTRL+Z) and Redo (CTRL+Y) can be used to restore the circuit.

Download Fall 2012 Circuit Files
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