Page 43 - Understanding Automotive Electronics

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2 THE SYSTEMS APPROACH TO CONTROL AND INSTRUMENTATION

the subject into its component parts based on functional groups. This chapter
will lay the foundation for a discussion by explaining the concepts of a system
and a subsystem, and how such systems function. The means for
characterizing the performance of any system will be explained so that the
reader will understand some of the relative benefits and limitations of
automotive electronic systems. This chapter will explain generally what a
system is and, more precisely, what an electronic system is. In addition, basic
concepts of electronic systems that are applicable to all automotive electronic
systems, such as structure (architecture) and quantitative performance analysis
principles, will be discussed.
Two major categories of electronic systems—analog or continuous time
and digital or discrete time—will be explained. In most cases, it is theoretically
possible to implement a given electronic system as either an analog or digital
system. The relatively low cost of digital electronics coupled with the high
performance achievable relative to analog electronics has led modern
automotive electronic system designers to choose digital rather than analog
realizations for new systems.

CONCEPT OF A SYSTEM
A system is a collection of components that function together to perform a
specific task. Various systems are encountered in everyday life. It is common
practice to refer to the bones of the human body as the skeletal system. The
collection of highways linking the country’s population centers is known as the
interstate freeway system.
Electronic systems are similar in the sense that they consist of collections of
electronic and electrical parts interconnected in such a way as to perform a specific
function. The components of an electronic system include transistors, diodes,
resistors, and capacitors, as well as standard electrical parts such as switches and
connectors among others. All of these components are interconnected with
individual wires or with printed circuit boards. In addition, many automotive
electronic systems incorporate specialized components known as sensors or
actuators that enable the electronic system to interface with the appropriate
automotive mechanical systems.
Systems can often be Any electronic system can be described at various levels of abstraction,
broken down into sub- from a pictorial description or a schematic drawing at the lowest level to a
systems. The subsystems block diagram at the highest level. For the purposes of the present discussion,
also consist of a number this higher-level abstraction is preferable. At this level, each functional
of individual parts. subsystem is characterized by inputs, outputs, and the relationship between
input and output. Normally only the system designer or maintenance
technician would be concerned with detailed schematics and the internal
workings of the system. Furthermore, the only practical way to cover the vast
range of automotive electronic systems is to limit our discussion to this so-
called system level of abstraction. It is important for the reader to realize that
there are typically many different circuit configurations capable of performing
a given function.

30 UNDERSTANDING AUTOMOTIVE ELECTRONICS