Chapter 3 - Digital Logic Test

Abstract

This chapter presents the fundamentals of semiconductor digital logic network testing. Digital circuits, unlike analogs, deal with discrete pulses known as digits. In these types of networks, discrete signals in the form of either pulse or voltage levels are manipulated as discrete quantities. These discrete quantities are the representations of logical high or logical low. The internal circuitry between input and output can be very complex. The diode structures protect the internal device circuitry from damage by static charges during product handling. The main device circuitry is located in the box named the logic circuit, which can be any type of complex structure. Functional testing is the application of a train of pulses to the input pins of the DUT and checking the outputs for their response. The input stimuli and the output sensing are determined by the logic function of the device given by the manufacturer. Hysteresis in small amounts helps the rapid switching action of internal clocks and covers wide temperature variations. Voltage hysteresis is the difference between the positive-going input voltage when the output switches, and the negative-going input when the output switches again. It has been found that the binary search method reduces the test loop to not more than eight, which, in traditional methods, is in the order of tens for a fine measurement.