Digital circuits and systems pdf

Unsourced material may digital circuits and systems pdf challenged and removed. A digital signal has two or more distinguishable waveforms, in this example, high voltage and low voltages, each of which can be mapped onto a digit. Digital techniques are helpful because it is a lot easier to get an electronic device to switch into one of a number of known states than to accurately reproduce a continuous range of values. Compared to vacuum tubes, transistors have many advantages: they are smaller, and require less power than vacuum tubes, so give off less heat.

Silicon junction transistors were much more reliable than vacuum tubes and had longer, indefinite, service life. Transistorized computers could contain tens of thousands of binary logic circuits in a relatively compact space. July 1958, successfully demonstrating the first working integrated example on 12 September 1958. In the early days of simple integrated circuits, the technology’s large scale limited each chip to only a few transistors, and the low degree of integration meant the design process was relatively simple. Manufacturing yields were also quite low by today’s standards. For example, a continuous audio signal transmitted as a sequence of 1s and 0s, can be reconstructed without error, provided the noise picked up in transmission is not enough to prevent identification of the 1s and 0s. In a digital system, a more precise representation of a signal can be obtained by using more binary digits to represent it.

Computer-controlled digital systems can be controlled by software, allowing new functions to be added without changing hardware. Often this can be done outside of the factory by updating the product’s software. So, the product’s design errors can be corrected after the product is in a customer’s hands. Information storage can be easier in digital systems than in analog ones.

The noise-immunity of digital systems permits data to be stored and retrieved without degradation. In an analog system, noise from aging and wear degrade the information stored. In a digital system, as long as the total noise is below a certain level, the information can be recovered perfectly. In some cases, digital circuits use more energy than analog circuits to accomplish the same tasks, thus producing more heat which increases the complexity of the circuits such as the inclusion of heat sinks.

In portable or battery-powered systems this can limit use of digital systems. Such base stations can be easily reprogrammed to process the signals used in new cellular standards. Digital circuits are sometimes more expensive, especially in small quantities. Most useful digital systems must translate from continuous analog signals to discrete digital signals. In some systems, if a single piece of digital data is lost or misinterpreted, the meaning of large blocks of related data can completely change. Digital fragility can be reduced by designing a digital system for robustness. In a state-machine, the state transition logic can be designed to catch unused states and trigger a reset sequence or other error recovery routine.