tailieunhanh - Logic kỹ thuật số thử nghiệm và mô phỏng P6

Digital circuits have always been designed to operate beyond the point where they could be reliably manufactured on a consistent basis. It is a simple matter of economics: By pushing the state of the art—that is, aggressively shrinking feature sizes, then testing them and discarding those that are defective—it is possible to obtain greater numbers of ICs from a single wafer than if they are manufactured with more conservative feature sizes (cf. Section for more discussion on this practice). This strategy depends on having access to complex, and sometimes very expensive, test equipment. This strategy also depends on being. | CHAPTER 6 Automatic Test Equipment INTRODUCTION Digital circuits have always been designed to operate beyond the point where they could be reliably manufactured on a consistent basis. It is a simple matter of economics By pushing the state of the art that is aggressively shrinking feature sizes then testing them and discarding those that are defective it is possible to obtain greater numbers of ICs from a single wafer than if they are manufactured with more conservative feature sizes cf. Section for more discussion on this practice . This strategy depends on having access to complex and sometimes very expensive test equipment. This strategy also depends on being able to amortize tester cost over many hundreds of thousands or millions of ICs. As ICs become more complex running at faster clock speeds with greater numbers of I O pins requirements on the tester become greater. More pins must be driven and monitored. Tolerances grow increasingly tighter and there is less margin for error. Clock skew and jitter must be controlled more tightly and the increasing amount of logic running at ever higher clock speeds requires the ability to switch greater amounts of current in less time. Early testers were quite simple Input pins were driven by stimuli stored in memory. After some predetermined clock cycle the output pins were strobed and their responses compared to expected responses cf. Figure . Many early testers were designed and manufactured by end users particularly mainframe vendors. With time however and the increasing complexity of the ICs and PCBs being tested it became prohibitively expensive to design and build these testers. Companies were formed for the explicit purpose of designing and building complex testers and although these testers were quite expensive it was nevertheless more economical to buy than to build in-house. Over the years many tester architectures and test strategies have evolved in order to locate defects in ICs and PCBs and provide