Technical Information Site of Power Supply Design

2020.09.23 Simulation

# Summary

Foundations of Electronic Circuit Simulation

This article concludes the series "Fundamentals of Electronic Circuit Simulation". As a final summary, the key points of each of the articles are listed below.

Fundamentals of Electronic Circuit Simulation

## Key Points:

・Software-based simulations are widely used in the design and evaluation of electronic circuits.

・Through software simulations, simple and quick evaluations become possible, and the time and processes involved in development can be reduced.

・Various simulator packages based on SPICE can be obtained.

2. SPICE Simulators and SPICE Models

## Key Points:

・Free SPICE simulator versions are provided by simulator vendors, and can be downloaded and used.

・In order to simulate circuits using ICs or other components, SPICE models for the components, which provide parameter information for the devices, are necessary.

3. Types of SPICE simulation: DC Analysis, AC Analysis, Transient Analysis

## Key Points:

・SPICE-based simulators are provided with functions for DC analysis, AC analysis, transient analysis, Monte Carlo analysis, S parameter and Fourier analysis, and noise analysis, among others.

・Nearly all simulator software packages are provided with functions for DC analysis, AC analysis, transient analysis, and Monte Carlo analysis.

4. Types of SPICE simulation: Monte Carlo

## Key Points:

・SPICE-based simulators are provided with functions for DC analysis, AC analysis, transient analysis, Monte Carlo analysis, S parameters, Fourier analysis, noise analysis, and the like.

・Monte Carlo is a general term used for methods in which random numbers are employed in simulations and numerical calculations, and is used to take component variation into consideration.

・Monte Carlo settings are different depending on the simulator.

5. Convergence Properties and Stability of SPICE Simulations

## Key Points:

・When using a SPICE-based simulator, if there are analysis errors or unstable results, there may be problems with convergence or stability.

・In some cases, problems with convergence and stability can be avoided by changing the settings of the SPICE simulator.

・It is difficult for the user to resolve problems if the device model has defects.

6. Types of SPICE Model

## Key Points:

・There are two types of SPICE models: “device models” and “subcircuit models”.

・Basically, ”device models” are models for discrete devices like transistors or diodes or like.

・”Subcircuit models” are basically a combination of “device models”.

7. SPICE Device Models: Diode Example--Part 1

## Key Points:

・There are two types of SPICE models: “device models” and “subcircuit models”.

・In SPICE device model, each parameter value is set.

8. SPICE Device Models: Diode Example--Part 2

## Key Points:

・There are two types of SPICE models: “device models” and “subcircuit models”.

・Characteristics can be adjusted by changing parameter values of device models.

・Device models are based on theoretical equations, and so simulation results are limited to the range that can be expressed by such equations (in some cases they may differ from actual behavior).

9. SPICE Subcircuit Models: MOSFET Example―Part 1

## Key Points:

・There are two types of SPICE models: “device models” and “subcircuit models”.

・Subcircuit models consist of connection information and device models.

・Subcircuit models may be constructed by imparting realistic characteristics to device models that represent ideal characteristics, and may constitute circuits with specific functions or the like.

10. SPICE Subcircuit Models: MOSFET Example―Part 2

## Key Points:

・There are two types of SPICE models: “device models” and “subcircuit models”.

・Subcircuit models consist of connection information and device models.

・Subcircuit models may be constructed by imparting realistic characteristics to device models that represent ideal characteristics, and may constitute circuits with specific functions or the like.

11. SPICE Subcircuit Models: Models Using Mathematical Expressions

## Key Points:

・In addition to subcircuit models that combine device models, there are also subcircuit models based on mathematical expressions.

・The mathematical expressions can be adjusted in keeping with device characteristics, so that high reproducibility is obtained.

・Models are complex, and so simulation times are longer, and convergence errors tend to occur.

## Key Points:

・SPICE models include thermal models which are used to perform simulations relating to heat.

・A thermal model is a model of an electrical circuit that corresponds to transient thermal resistances, for use in calculations of the thermal circuit associated with the electrical circuit.

・By applying the power dissipation Pd as a current I to a thermal model Rth, the junction temperature Tj can be monitored as corresponding to a voltage.

## Key Points:

・The Thermal Dynamic Model is a SPICE model that incorporates the Thermal Model and represents changes in characteristics due to heat generation of the component itself.

・The Thermal Dynamic Model is a model in which the Thermal Model is added to the subcircuit for a device.

・The incorporated Thermal Model is used to calculate Tj, and the Tj is reflected in the electrical characteristics of the device.