Running a Simulation

1. Overview

Aquarius can perform three main types of simulation namely, Steady State (DC), Transient (time dependant) and Curve Trace. Simulations can also be re-started from existing simulations as a continuation run from an initial condition.

info

To run any simulation, the circuit must be correctly connected and meet the requirements for a valid configuration. This includes having at least one device (.sdm), at least one source, and a ground reference. All nodes must be properly connected, no floating or unconnected nodes are allowed.

For a DC simulation, this means at least one DC source must be present.
For a transient simulation, this means at least one transient source must be included.
For an IV trace, this means one and only one IV‑trace source must be defined.

2. Steady State

To perform a steady state simulation from the circuit simulator:

1. Press the blue run button, or alternatively in the menu use Simulation → Steady State.

3. Transient

To perform a transient simulation from the circuit simulator:

1. Press the orange run button, or alternatively in the menu use Simulation → Transient.

4. Curve Trace

A curve trace simulation is a type of steady-state simulation used to characterise the electrical behaviour of semiconductor devices. This type of simulation uses an IV Curve Tracing Algorithm and may be preferred over a simple DC source with fixed steps because it provides more precise control over the sweep profile, allowing for accurate capture of rapid current changes and non-linear device behaviour which enables finer resolution around critical operating points. For more information see IV Curve Tracer.

To perform a curve simulation from the circuit simulator:

1. Press the purple run button, or alternatively in the menu use Simulation → IV Trace.

5. Start from Initial Condition

Simulations can be started from the results of a previous run to continue from an established initial condition. This approach is often useful when the numerical complexity of a model prevents the solver from converging directly from the default starting state. By first computing a stable operating point and then restarting from that solution, more challenging bias conditions can be explored. Restarting is particularly helpful in cases such as:

• Sweeping a contact bias through a region where direct convergence is difficult (e.g., sweeping a JFET gate voltage from a negative starting value).
• Gradually ramping a bias voltage to prepare for a transient analysis, such as modelling reverse‑recovery behaviour.

To restart from an existing simulation:

1. Press the initial condition button, or alternatively in the menu use Simulation → Specify an Initial Condition. A dialog will appear.
2. Click the Select... button, a file dialog will open. Select the .res file which you would like to use an as initial condition.

3. Once the file has loaded select the starting case which you would like to use an the initial condition.

4. Click the OK button to confirm this selection.

5. Should you wish to modify the initial condition settings click the down arrow next to the initial condition button and click Specify an initial condition, then repeat steps 2 - 4.

When the Restart button is clicked, it toggles the use of an initial condition on or off. If the button is highlighted in blue, the simulation will start from the saved initial condition. When the button is in its default, non‑highlighted state, the initial condition is not used, and the simulation will start normally.

danger

When restarting a simulation from a saved initial condition, the circuit netlist must be identical to the netlist used in the original simulation. Any modification to the circuit such as adding, removing, or renaming components, nodes, or connections will cause the simulation to fail. You can change the type of a voltage source however its name and all of its connections must remain exactly the same.