![]() CMOS with its rugged flakiness was used when power drain had to be kept to a minimum, and for certain devices where its peculiarities were valuable, as in ripple counters and the 4046, for example. Bipolar devices, somwhat inappropriately called TTL (transistor-transistor logic), early became the most popular choice, together with NMOS large-scale devices that imitated TTL properties. Their circuit properties are quite different, although modern devices can actually be used together (this is not usually a good practice, however). The two kinds are bipolar ("TTL") and CMOS, and both are about as old as integrated circuits themselves. There are more varieties, some quite esoteric, but these two handle most of the load, and are the only ones easily available for study and use. There are two kinds of digital integrated circuits in common use. We will not be very interested in the information carried by the digital signals. Here, I want to discuss mainly the electronic or circuit aspects of the integrated circuits used in digital devices, which is of great utility in practical work. The science of digital logic is presented in texts and courses in Digital Design, to which the reader is referred for a great deal of interesting information, most of which is not used in practical work, at least not any more. In digital systems, a limited number of circuit states, usually two in the nearly universal binary logic, contain the information, instead of the continuously variable information in an analog signal. Circuit Properties of LS and HC Digital Logic ![]()
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