1. Popular Circuit Simulation Software and Its Features
Circuit simulation is a component of electronic design automation (EDA). Circuit simulation is generally divided into three levels: physical level, circuit level, and system level. The focus in teaching is primarily on circuit-level simulation.
Circuit-level simulation analyzes the performance of circuits composed of components, including logic simulation for digital circuits and AC/DC analysis, transient analysis for analog circuits, etc. Circuit-level simulation must be supported by a component model library, with simulated signals and waveform outputs replacing signal sources and oscilloscopes in actual circuit debugging. Circuit simulation mainly verifies the correctness of the design scheme in terms of functionality. Circuit simulation technology allows designers to comprehensively understand various characteristics of the circuit before the actual electronic system is produced. Currently, the more popular circuit simulation software includes: ORCAD, Protel, Multisim, TINA, ICAP/4, Circuitmaker, Micro-CAP, and Edison, among others.
Basic Features of Circuit Simulation Software:
● Number and Performance of Simulation Projects:
The number of simulation projects is the main indicator of circuit simulation software. The basic functions common to various circuit simulation software include: static operating point analysis, transient analysis, DC scanning, and AC small-signal analysis; potential analyses include: Fourier analysis, parameter analysis, temperature analysis, Monte Carlo analysis, noise analysis, transfer function, DC and AC sensitivity analysis, distortion analysis, pole and zero analysis, and more. Simulation software like SIMextrix has only 6 simulation functions, while Tina 6.0 has 20, and Protel, ORCAD, P-CAD, etc., have about 10 simulation functions. Specialized circuit simulation software has more simulation functions, considering various needs for electronic design and teaching. For example, TINA’s symbolic analysis, Pspice and ICAP/4’s component parameter variable and optimization analysis, Multisim’s network analysis, and CircuitMaker’s error settings are all relatively distinctive features.
Pspice is proficient in analyzing analog circuits, but not very effective in handling digital circuits. For pure digital circuit analysis and simulation, simulation software based on hardware description languages such as VHDL is preferred, for example, Altera’s programmable logic device development software MAX+plusII.
● Number and Accuracy of Simulation Components:
The number and accuracy of simulation components in the component library determine the applicability and precision of the simulation. The component libraries of circuit simulation software contain thousands to tens of thousands of simulation components, but the component models included in the software always lag behind the production and application of actual components. Therefore, in addition to the device library within the software, the websites of component manufacturers are an important source for component models. A wealth of online information can also provide useful simulation models. If designers conduct in-depth research on simulation component models, they can customize component models based on the latest external characteristic parameters of components to build their own component libraries. For educators, the component model library within the software can generally meet regular teaching needs, with the main issue being the substitution of domestic components for foreign ones and establishing a library of commonly used domestic components in teaching.
Circuit simulation software classifies components in two ways: by component type such as power supplies, diodes, 74 series, etc., into several large categories; or by manufacturer classification. Most simulation software provides previews of circuit graphical symbols for easy selection.
Each circuit simulation software simplifies the PSPICE model of components. For example, the resistance model in PSPICE has three temperature coefficients: first-order, second-order, and exponential. Most software only defines the first two temperature coefficients, while only TINA defines all three temperature coefficients for resistors, and Protel does not define temperature coefficients for resistors; for instance, bipolar transistors have 40 PSPICE model parameters, with Multisim specifying all parameters, TINA having 32, and Protel only 22. Designs requiring high simulation accuracy should use high-precision component models or adjust parameter models based on actual components.
● Data Display and Processing Capabilities:
Running simulations generates a large amount of data. The display methods for simulation data include lists and graphs. For example, after calculating the static operating point, Protel displays data such as node voltage, branch current, component energy consumption, and equivalent resistance of power supply in a list; Pspice and Micro-CAP can label voltage, current, and power on the circuit diagram. Transient analysis, DC scanning, and AC small-signal analysis generally display results graphically. Graphs can be printed or saved in specific file formats; some software can save waveforms as common PEL (represented by time-electrical quantity pairs) format files, or export to Excel. Graphs can also be copied and pasted into Windows Paint for processing and saving as image files; or directly pasted into documents of Word, PowerPoint, Authorware, etc.
Each circuit simulation software has different capabilities for processing waveform graphs. However, they generally have the following data processing functions:
1.Waveform Measurement: Displayed in different types of coordinate scales (linear, logarithmic, amplitude, decibel, etc.), measuring effective value, root mean square value, peak-to-peak value, average value, maximum value, minimum value, period, etc.
2.Graph Calculation: Performing addition, subtraction, multiplication, division, differentiation, integration, etc., on graphs, or using graph variables as independent variables of mathematical functions to obtain new mathematical variables.
3.Graph Decoration: Making graphs more aesthetically pleasing and easier to understand. You can change the thickness, color, style, and markers of the graph; add measurement data point markers and data labels; change the background color of the graph, coordinate styles, and colors, etc. Some software allows for the entry of explanatory text in the graph display, even in Chinese.
● Virtual Instruments and Educational Functions:
Visual virtual instruments are a feature of circuit simulation software. A typical example is Multisim, which has achieved the highest level in both interface appearance and internal functionality among similar software. Other software with virtual instrument settings includes TINA, Edison, etc.
Virtual instruments can help learners understand the role of electronic instruments and gain a deeper understanding of electronic measurement methods and techniques. Mastering various operational methods for electronic instruments, especially the functions of various control buttons and knobs. The functions of virtual instruments in Multisim and TINA actually exceed those of PSPICE itself, with notable examples being the network analyzer and logic analyzer. The network analyzer is a dedicated instrument for analyzing RF components and RF network parameters; while Multisim’s logic analyzer has real digital circuit analysis capabilities that meet the technical requirements for analyzing actual digital systems. Some software also features virtual electromechanical components, such as bulbs, buttons, relays, contactors, etc. By using these components, electromechanical control circuits can be constructed. The mathematical and simulation control devices in the software’s component library can be used for automatic control principle analysis.
To meet the educational needs for teaching circuit principles, some software has set up educational functions. Primarily, this allows users to set some hidden errors for components. For instance, Multisim and TINA can set parameters for components to simulate open circuits, short circuits, and leakage resistance; while Altium’s CircuitMaker can make more teaching settings for components and circuits and can even be password-protected, serving directly as an examination tool for practical training courses.
2. Comparison of Major Simulation Software
1. ELECTRONICS WORKBENCH EDA (hereinafter referred to as EWB):
EWB software was launched by Interactive Image Technologies Ltd in Canada in the early 1990s, but it began to be used in China only in recent years. The version commonly used now is EWB 5.0, which operates under the WIN95 environment (a demonstration version of 6.0 has been seen in China; note that EWB 5.0 can also run in the WINDOWS 3.1 environment but requires the installation of WING32 tools). Compared to other EDA software, it is relatively small, only 16M, and has relatively simple functions, conducting mixed simulation of analog and digital circuits. However, do not underestimate it; its simulation capabilities are extremely powerful, almost achieving 100% accuracy in simulating real circuit results. It provides tools such as multimeters, oscilloscopes, signal generators, frequency analyzers, logic analyzers, digital signal generators, and logic converters on the desktop. Its component library includes many transistor components, integrated circuits, and digital gate circuit chips from major companies. Components not included in the library can also be imported from external modules. Among various circuit simulation software, EWB is the easiest to get started with, as its interface is very intuitive, with the schematic and various tools in the same window. A person who has never used it can become proficient with a little study. For electronic designers, it is an excellent EDA tool, allowing you to see the results of many circuits without needing a soldering iron. Additionally, if you want to change components or modify component parameters, you just need to click the mouse. It can also be used as a supplementary teaching software for electrical knowledge, allowing users to see various circuit output waveforms directly from the screen. EWB also has good compatibility, as its file format can be exported to formats readable by ORCAD or PROTEL. This software is only available in English; under the Chinese version of WINDOWS 98, some of its icons may shift two positions (it works normally under WINDOWS 95), but this does not affect its use.
2. PROTEL:
PROTEL was launched by PORTEL, an Australian company, in the late 1980s as EDA software. It is undoubtedly at the forefront of CAD software in the electronics industry and is the preferred software for electronic designers. It was used early on in China and has the highest popularity, with some schools even offering courses specifically to learn it. Almost all electronic companies use it, and many large companies list proficiency in PROTEL as a requirement when hiring electronic design talent. Early PROTEL primarily served as an automatic routing tool for printed circuit boards and operated in a DOS environment with low hardware requirements, running on a hard disk-less 286 machine with just 1M of memory. However, it had limited functions, only offering electrical schematic drawing and printed circuit board design, with a low routing success rate. Today’s PROTEL has evolved to PROTEL 99SE, a massive EDA software package, fully installed at over 200MB, working in the WINDOWS 9X environment. It is a complete, all-encompassing electronic design system at the board level, including electrical schematic drawing, mixed signal simulation of analog and digital circuits, multi-layer printed circuit board design (including automatic routing), programmable logic device design, chart generation, electronic spreadsheet generation, macro operation support, and more, featuring a Client/Server architecture. It also supports file formats from other design software, such as ORCAD, PSPICE, EXCEL, etc., achieving 100% routing success for high-density PCBs.
3. PSPICE:
PSPICE is one of the earliest EDA software, launched by MICROSIM in 1985. In terms of circuit simulation, it is arguably the most powerful, widely used in China. The version most commonly used now is PSPICE 6.2, which operates in a WINDOWS environment and occupies over 20MB of hard disk space. The software consists of schematic editing, circuit simulation, stimulus editing, component library editing, waveform graphs, and several other parts, functioning as a whole but with each part having its own window. PSPICE has now been merged into ORCAD, becoming ORCAD-PSPICE, yet PSPICE is still sold and used separately, with the latest version being PSPICE 9.1, which works on WINDOWS 95/98/NT platforms, requiring a Pentium CPU or higher, 32M memory, over 50M of remaining hard disk space, and a display resolution of 800X600 or higher. It is a powerful simulation EDA software for mixed analog and digital circuits, capable of performing various circuit simulations, stimulus establishment, temperature and noise analysis, analog control, waveform output, data output, and displaying both analog and digital simulation results in the same window simultaneously. It can accurately simulate any device or circuit, including IGBT, pulse-width modulation circuits, analog/digital conversion, and more. For components not included in the library, users can also edit them themselves.
The following Table 2-1 provides statistics on the main parameters of 10 representative circuit simulation software. The installed capacity in the table refers to the space occupied by the software on the hard disk after installation. The number of power types depends on how the software classifies power supplies; some software separates the same power supply into multiple directories, while others group five types of transient analysis sources under one icon. PSPICE’s official version has 16,000 simulation components.
From the above table comparison, it can be seen that among commonly used circuit simulation software, Multisim 2001 stands out in performance, both in terms of the number of components in the simulation component library and the variety of virtual devices and analyses available, especially in the hidden settings for circuit faults, which greatly facilitates teaching. It is worth mentioning that Multisim 2001 is an upgraded version of the well-known simulation software EWB, with performance improved many times over. Therefore, the circuit simulation software commonly used in teaching today is either EWB or Multisim 2001, which can fully meet the various experimental, simulation, and assessment needs in teaching and is the preferred software for educational purposes.