Circuit simulation

- an overview of the ways in which electronics can be simulated during the electronics design process. An overview of the SPICE simulation software is also given.

The design cycles for electronics design are becoming much shorter, while at the same time circuits are becoming more complicated. This problem is one that is present in all aspects of electronics design.

This is being felt in many areas of the electronics industry, from commercial products such as mobile phones and wireless routers, to larger items such as computers, and highly sophisticated communications and control items. Within all of these fields there is a growing expectation that the hardware will work first time.

Application of circuit simulation software

There are many steps that have been taken to improve the accuracy of electronics hardware design. One of the chief areas is that of circuit simulation. By using circuit simulation software the design can be created in software and many of the problems addressed before the design is committed to hardware. In this way problems can be detected and changed very easily.

Circuit simulation software also provides more information more easily than building a prototype circuit. For example, the performance of a circuit is affected by the variation in components within their allowed tolerance. Circuit simulation software is able to predict these changes and the results on the performance of the electronics circuit as a whole.

In addition to this, some aspects of operation may not be accurate compared to the final PCB. These include parasitic resistances and capacitances. In radio frequency applications these parasitic elements are very important and included into the model of the circuit being simulated. In these cases it is usual to perform Monte Carlo simulations using the circuit simulation software. This is a task which is impractical using calculations by hand.

Circuit simulation software options

There is a variety of circuit simulation software available and there are effectively three types of source that can be used:

  • Specific circuit simulation programmes:   There is a wide variety of programmes available varying in price considerably. Some are available at reasonable costs, but those offering many facilities are normally very expensive
  • Vendor supplied programmes   These programmes are normally designed to provide simulation for circuits using components from a particular vendor, and they are normally not applicable for general circuit simulation
  • Open source programmes   There are many of these available, but they are probably not the best option for commercial companies to rely on because there can be little or no support. Despite this they can still work well under most circumstances.

Many circuit simulation programmes are based on SPICE (Simulation Program with Integrated Circuits Emphasis). SPICE is a general purpose, but very powerful analogue circuit simulator. It is used in IC and board-level design to simulate circuits in order to predict their behaviour.

SPICE circuit simulation overview

The SPICE circuit simulation programme was originally developed at the Electronics Research Laboratory of the University of California, Berkeley in 1975. The first two versions used FORTRAN as the base language and they ran on the large mainframe computers of the day. Later, version 3 of the SPICE simulation programme was coded in C, but it still used many FORTRAN like constructions.

The original versions of the SPICE simulation software had a number of limitations, but as later versions were introduced, the SPICE simulation programmes grew in sophistication. Elements such as transistors could be modelled as non-linear voltage and current-dependent components.

The SPICE simulation software was upgraded by a number of different organisations, each offering their own flavour. Each version of SPICE includes an advertising clause and distribution restrictions for countries not considered friendly to the USA. Nowadays there are many versions of SPICE simulation software available. Many are available free on the Internet, and there are versions for Windows, Linux and the Mac.


With the availability and ease of use of circuit simulation software, inlcuding such programmes as the SPICE circuit simlation package, it is easy to simulate circuits before they are built. In this way it is much faster to construct working circuits as it is possible to design the circuit and optimise its operation before it is even built. By doing this electronics design can be much faster, more accurate and much cheaper.

By Ian Poole

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