How do you handle complex and nonlinear circuits and devices in SPICE simulation?

1 Choose the right model

One of the first steps in SPICE simulation is to choose the appropriate model for your circuit or device. A model is a set of equations and parameters that describe the behavior and characteristics of a component. SPICE provides various built-in models for common devices, such as MOSFETs, BJTs, LEDs, and op-amps. However, these models may not be accurate or suitable for your specific application or design. Therefore, you may need to modify the existing models or create your own custom models using subcircuits, macros, or behavioral sources. You can also use external libraries or data sheets to find more realistic and detailed models for your components.

2 Adjust the simulation settings

Another step in SPICE simulation is to adjust the simulation settings to match your circuit or device requirements. These settings include the type of analysis, the time step, the convergence criteria, the tolerance, the temperature, and the initial conditions. Depending on the complexity and nonlinearity of your circuit or device, you may need to tweak these settings to achieve a stable and accurate simulation. For example, you may need to increase the time step or the tolerance for fast or sensitive circuits, or use a DC sweep or a transient analysis for nonlinear or dynamic circuits. You can also use commands or options to control the simulation behavior, such as .OPTIONS, .IC, .NODESET, .UIC, and .MEASURE.

3 Simplify the circuit or device

A third step in SPICE simulation is to simplify the circuit or device as much as possible without compromising the essential functionality and performance. This can help reduce the simulation time and the computational resources, as well as avoid potential errors or conflicts. You can simplify the circuit or device by eliminating unnecessary components, replacing complex components with equivalent ones, using ideal or linear components when possible, and using symmetry or periodicity to reduce the size or number of components. You can also use techniques such as nodal analysis, Thevenin's theorem, Norton's theorem, or superposition to simplify the circuit or device.

4 Verify the results

A final step in SPICE simulation is to verify the results and check for any errors or discrepancies. You can verify the results by comparing them with theoretical calculations, experimental measurements, or other simulation tools. You can also use plots, graphs, tables, or reports to visualize and analyze the results. You should look for any signs of instability, divergence, oscillation, distortion, or noise in the results, and identify the possible causes and solutions. You should also evaluate the accuracy and validity of the results, and consider the effects of parasitics, noise, temperature, and other factors that may affect the real-world performance of your circuit or device.

5 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?