Built In Test for VLSI: Pseudorandom Techniques

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Digital Testing and the Need for Testable Designs

Testing of digital circuits is a major portion of the effort in their design, production, and use. As the electronics industry evolved from discrete components, through the early integrated circuits that contained a single gate or flip-flop per package, to increasingly high levels of integration, the demands on testing methods and their effectiveness have caused test technology to evolve to a high degree of sophistication. As the number of circuits that can be integrated into one piece of silicon approaches one million, it would seem that some small portion of those circuits could be devoted to the testing or assurance of the function the remainder are intended to implement. This concept is called “built-in test” and will be explored in this book.

When digital electronics consisted entirely of discrete components (vacuum tubes, transistors, resistors, capacitors, and diodes), testing was essentially done in three parts. First, each individual part was tested to a specification. Second, these parts were assembled into digital elements—gates, flip-flops, and so forth—and the elements were tested to determine whether they performed their intended function. Finally, functional testing was done at the application or system level, where ...