With the advent of LSI and subsequently VLSI, technology has never
witnessed such an unprecedented growth in the use of electronic systems in a
wide range of applications. Although the ability to integrate several hundreds
of thousands of transistors into a monolithic integrated circuit offers many
advantages, a major concern in the design of these complex devices has been
the ability to verify and in some instances guarantee their fault free operation.
The testing of digital circuits has been problematic since time immemorial;
however with the introduction of VLSI the problems have been aggravated by
several factors in addition to those associated with the increase in complexity
and reduction in the pin to gate ratio.
• Market trends have encouraged the prolific use of VLSI in many
applications ranging from consumer products to critical commercial
controllers, consequently reliability is of paramount importance.
• The increased requirement for ASICs, has necessitated the development of
more sophisticated CAD tools. However, the greatest advances have been
in layout and simulation with little improvement in area of test.
Consequently, inexperienced designers can now produce extremely
complex but untestable chips.
• Again, with the introduction of ASICs the high costs of testing cannot be
amortized over a large number of components since ASICs are inherently
low volume products.
• Traditionally the design and test of a circuit were considered as two distinct
phases in the development of an electronic system. Designers must now be
educated that in order to pnxluce testable VLSI circuits testing must be
considered as an integral part of the design process.
Hence the objectives of this text are. first, to emphasize that testing is an
integral part of the design process and must not be considered as an after-
thought. Secondly, it summarizes the new developments in simulation, test
and design for testability about which a vast amount of research work has
been produced and which is disseminated over a large number of technical