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.
Summary
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.
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