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What is Circuit Simulation? Its Advantages and Types

Designing electrical and electronic circuits is time taking, technically intensive and not to mention is a costly affair. After designing the circuit, engineers need to test its functionality to validate the working and make necessary changes. What if instead of actually building the circuit using real components and boards, we could somehow get a mathematical characterization of the circuit? This is the concept of Circuit Simulation. We will explore more about the same in this guide and also take a look at different types circuit simulations.

Outline

What is Circuit Simulation?

We are surrounded by electronics. In fact, it is very difficult to imagine the World working as it is today (fast-paced, information on the go, convenient controls etc.) without electronics.

Due to the sheer number of devices, appliances and gadgets releasing day-by-day, it is important to maintain an efficient manufacturing process and also comply to various technical standards and regulations.

In this process, electrical and electronics engineers prepare a mathematical model of a circuit to observe the behavior of the circuit without actually building it (with real, physical components). This technique of modelling a circuit using mathematical expressions to check and verify the design of electrical and electronic circuits is known as Circuit Simulation.

If we compare circuit simulation to other forms of simulation such as Logic Simulation and Functional Simulation, it uses detailed physical models (in the form of mathematical expressions) of various circuit elements to solve for complex differential and algebraic equations. The result is an accurate simulation with precise time waveforms of node voltages and component currents.

Need for Circuit Simulation

• It is clear that using circuit simulation, we can test the functionality of a circuit without actually building the circuit.
• Circuit simulation is cost efficient, time saving and we can easily design complex circuits using the software. This saves design engineers and companies a lot of time and money.
• Engineers can reduce the wastage of valuable hardware resources and proceed to build hardware only after they get satisfactory and accurate results from simulation.
• We can easily re-design the circuit based on the simulation results. At each stage of design and simulation, engineers can verify the performance and compare it to the theoretical responses.
• Circuit Simulation Software is the starting point of a new concept or idea. You could also modify existing projects without designing PCBs.
• Just like physical probing and observing waveforms on an oscilloscope, we can do the same in circuit simulation. You can easily probe different points in a circuit and view the virtual waveforms.

• Most of the popular circuit simulation software such as SPICE, LTspice etc. are free. There are some proprietary tools but even those are developed using SPICE algorithm.
• You can easily change the models and overall behavior of the simulator on the go. This helps you in iterating multiple levels of simulation to explore the limitations of the circuit.
• Changing the values of components is also very easy. Apart from component values, you could also test the circuit for different input parameters (voltages and currents).
• Testing memory related timings such as read and write times and latency of memory modules becomes very easy with dedicated analog simulation.
• You can also use simulators to analyze noise and cross talk in complex RF and high-speed designs.
• Apart from regular circuit, simulators also have tools for testing power supply designs (SMPS) and power distribution systems.
• Digital Simulators check the voltage levels for logic 0 and logic 1 while using Analog Simulators, you can check the duration of the transition between these logic levels.

Types of Circuit Simulation

Let us now see different types of circuit simulations. We can categorize simulation into the following three way:

• Analog Circuit Simulation
• Digital Circuit Simulation
• Mixed-Mode Circuit Simulation

Analog

As the name suggests, in analog simulation, we usually work with analog components and signals. In this simulation, the mathematical models must be highly accurate to run frequency domain (AC), time domain (transient) and non-linear quiescent (DC) modes.

SPICE and FastSPICE are two popular analog simulators that use very accurate linear and non-linear component models to analyze a circuit’s behavior.

Digital

When we compare the complex mathematical models of analog simulators, digital simulators are relatively simple. HDL such as Verilog and VHDL are the backbone of digital simulation.

Unlike analog simulators, where we need continuously varying signals, in digital simulation, we actually work with two discrete voltage levels. In digital electronics, we call them as Logic 0 and Logic 1.

Mixed-Mode

It is a combination of both analog and digital simulations. This type of simulation is very useful in mixed circuit system design and analysis. With the mixed-mode simulation, the analog and digital parts are separate entities with respective tools and resources.

Levels of Simulation

In the previous section, we saw different types of circuit simulation. These types define the type of circuit and its corresponding analysis steps we need to follow. But you can also define several levels of simulation based on the abstractness of the circuit.

• Block-Level Simulation: In this simulation, we divided different parts of several functional blocks and perform simulation on these blocks as a whole. This is very important is a modular design and also helps in reusing the existing functional blocks in other circuits as well.
• Chip-Level Simulation: As the name suggests, in a chip-level simulation, we take an integrated circuit (a chip) and simulate its functionality as a single entity. This ensures that the chip is working as intended.
• Memory Simulation: Memory is an important part of modern computer systems (large or small). Hence, there are dedicated tools and simulators to test the memory timings very accurately. You can simulate SRAM, DRAM, NAND Flash etc.
• Mixed-Signal Simulation: Modern system-on-chips or SOCs are actually a combination of several analog and digital functional elements. Hence, we can use mixed-signal simulation techniques to see how analog and digital signals behave and interact in a tight space.
• RF Simulation: While RF design is still magic to some people, engineers use complex RF simulation tools to test and verify various RF related IC such as mixers, amplifiers, PLLs, and many more.

Popular Simulation Software

There are several circuit simulator tools and software in the market. SPICE, which is short for Simulation Program with Integrates Circuit Emphasis, is an extremely popular circuit simulator. University of Berkeley’s Electronics Research Laboratory developed this software, originally intended for U.S. Department of Defense.

Since it is an open-source software, it became extremely popular choice for several other designer, who designed their own simulators using SPICE algorithms. One such tool is LTspice.

Another popular SPICE based circuit simulator is NI’s Multisim. But unlike LTspice, it is a paid software. Here is a list of some popular circuit simulator software.

• SPICE
• ngspice
• LTspice (SPICE)
• PSIM
• Multisim (SPICE)