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.




AC Analysis


I am running an AC analysis on one of my circuits. I have a sine source in the schematic that provides the AC stimulus. However, when I run the simulation, the output node that I am looking at is producing a constant 0 which is in error. In the AC analysis limits, I have disabled the Operating Point option and my State Variables option is set to 'Zero'. What is going wrong?


The definition of AC analysis is that it is a linear, small signal analysis. Micro-Cap constructs a small signal representation of the circuit for the analysis. Typically, Micro-Cap obtains the small signal models by linearizing the devices about the operating point calculations. However, if the Operating Point option is disabled, then it will use the settings from the State Variables option. Since it is set to Zero in this case, the circuit is creating a small signal model based on all the node voltages and inductor currents being zero which is producing the incorrect results. Either enable the Operating Point option or change the State Variables option to Read or Leave. If using the Read option, there must be a previously saved state variables file for the circuit, and if using the Leave option, there must be the correct values available in the State Variables Editor. The combination of disabled Operating Point and Zero for the State Variables Option should never be present for AC analysis.






AC Analysis
Analysis - General
DC Analysis
Dynamic DC
Initial Conditions
Monte Carlo
Schematic Editor
Transient Analysis