Digital electronics
Digital electronics is a field of electronics involving the study of digital signals and the engineering of devices that use or produce them. It deals with the relationship between binary inputs and outputs by passing electrical signals through logical gates, resistors, capacitors, amplifiers, and other electronic components. The field of digital electronics is in contrast to analog electronics, which work primarily with analog signals. Despite the name, digital electronics designs include important analog design considerations.
Large assemblies of logic gates, used to represent more complex ideas, are often packaged into integrated circuits. Complex devices may have simple electronic representations of Boolean logic functions.
History
The binary number system was refined by Gottfried Wilhelm Leibniz and he also established that by using the binary system, the principles of arithmetic and logic could be joined. Digital logic as we know it was the invention of George Boole in the mid-19th century. In an 1886 letter, Charles Sanders Peirce described how logical operations could be carried out by electrical switching circuits. Eventually, vacuum tubes replaced relays for logic operations. Lee De Forest's modification of the Fleming valve in 1907 could be used as an AND gate. Ludwig Wittgenstein introduced a version of the 16-row truth table as proposition 5.101 of Tractatus Logico-Philosophicus. Walther Bothe, inventor of the coincidence circuit, shared the 1954 Nobel Prize in physics, for creating the first modern electronic AND gate in 1924.Mechanical analog computers started appearing in the first century and were later used in the medieval era for astronomical calculations. In World War II, mechanical analog computers were used for specialized military applications such as calculating torpedo aiming. During this time the first electronic digital computers were developed, with the term digital being proposed by George Stibitz in 1942. Originally they were the size of a large room, consuming as much power as several hundred modern PCs.
Claude Shannon, demonstrating that electrical applications of Boolean algebra could construct any logical numerical relationship, ultimately laid the foundations of digital computing and digital circuits in his master's thesis of 1937, which is considered to be arguably the most important master's thesis ever written, winning the 1939 Alfred Noble Prize.
The Z3 was an electromechanical computer designed by Konrad Zuse. Finished in 1941, it was the world's first working programmable, fully automatic digital computer. Its operation was facilitated by the invention of the vacuum tube in 1904 by John Ambrose Fleming.
At the same time that digital calculation replaced analog, purely electronic circuit elements soon replaced their mechanical and electromechanical equivalents. John Bardeen and Walter Brattain invented the point-contact transistor at Bell Labs in 1947, followed by William Shockley inventing the bipolar junction transistor at Bell Labs in 1948.
At the University of Manchester, a team under the leadership of Tom Kilburn designed and built a machine using the newly developed transistors instead of vacuum tubes. Their "transistorised computer", and the first in the world, was operational by 1953, and a second version was completed there in April 1955. From 1955 and onwards, transistors replaced vacuum tubes in computer designs, giving rise to the "second generation" of computers. Compared to vacuum tubes, transistors were smaller, more reliable, had indefinite lifespans, and required less power than vacuum tubes - thereby giving off less heat, and allowing much denser concentrations of circuits, up to tens of thousands in a relatively compact space.
In 1955, Carl Frosch and Lincoln Derick discovered silicon dioxide surface passivation effects. In 1957 Frosch and Derick, using masking and predeposition, were able to manufacture silicon dioxide field effect transistors; the first planar transistors, in which drain and source were adjacent at the same surface. At Bell Labs, the importance of Frosch and Derick technique and transistors was immediately realized. Results of their work circulated around Bell Labs in the form of BTL memos before being published in 1957. At Shockley Semiconductor, Shockley had circulated the preprint of their article in December 1956 to all his senior staff, including Jean Hoerni, who would later invent the planar process in 1959 while at Fairchild Semiconductor. At Bell Labs, J.R. Ligenza and W.G. Spitzer studied the mechanism of thermally grown oxides, fabricated a high quality Si/SiO2 stack and published their results in 1960. Following this research at Bell Labs, Mohamed Atalla and Dawon Kahng proposed a silicon MOS transistor in 1959 and successfully demonstrated a working MOS device with their Bell Labs team in 1960. The team included E. E. LaBate and E. I. Povilonis who fabricated the device; M. O. Thurston, L. A. D’Asaro, and J. R. Ligenza who developed the diffusion processes, and H. K. Gummel and R. Lindner who characterized the device.
While working at Texas Instruments in July 1958, Jack Kilby recorded his initial ideas concerning the integrated circuit, then successfully demonstrated the first working integrated circuit on 12 September 1958. Kilby's chip was made of germanium. The following year, Robert Noyce at Fairchild Semiconductor invented the silicon integrated circuit. The basis for Noyce's silicon IC was Hoerni's planar process.
The MOSFET's advantages include high scalability, affordability, low power consumption, and high transistor density. Its rapid on–off electronic switching speed also makes it ideal for generating pulse trains, the basis for electronic digital signals, in contrast to BJTs which, more slowly, generate analog signals resembling sine waves. Along with MOS large-scale integration, these factors make the MOSFET an important switching device for digital circuits. The MOSFET revolutionized the electronics industry, and is the most common semiconductor device.
In the early days of integrated circuits, each chip was limited 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. The wide adoption of the MOSFET transistor by the early 1970s led to the first large-scale integration chips with more than 10,000 transistors on a single chip. Following the wide adoption of CMOS, a type of MOSFET logic, by the 1980s, millions and then billions of MOSFETs could be placed on one chip as the technology progressed, and good designs required thorough planning, giving rise to new design methods. The transistor count of devices and total production rose to unprecedented heights. The total amount of transistors produced until 2018 has been estimated to be .
The wireless revolution began in the 1990s and was enabled by the wide adoption of MOSFET-based RF power amplifiers and RF circuits. Wireless networks allowed for public digital transmission without the need for cables, leading to digital television, satellite and digital radio, GPS, wireless Internet and mobile phones through the 1990s2000s.
Properties
An advantage of digital circuits when compared to analog circuits is that signals represented digitally can be transmitted without degradation caused by noise. 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. While this requires more digital circuits to process the signals, each digit is handled by the same kind of hardware, resulting in an easily scalable system. In an analog system, additional resolution requires fundamental improvements in the linearity and noise characteristics of each step of the signal chain.
With computer-controlled digital systems, new functions can be added through software revision and no hardware changes are needed. Often this can be done outside of the factory by updating the product's software. This way, the product's design errors can be corrected even 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. Even when more significant noise is present, the use of redundancy permits the recovery of the original data provided too many errors do not occur.
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 the use of digital systems. For example, battery-powered cellular phones often use a low-power analog front-end to amplify and tune the radio signals from the base station. However, a base station has grid power and can use power-hungry, but very flexible software radios. Such base stations can easily be reprogrammed to process the signals used in new cellular standards.
Many useful digital systems must translate from continuous analog signals to discrete digital signals. This causes quantization errors. Quantization error can be reduced if the system stores enough digital data to represent the signal to the desired degree of fidelity. The Nyquist–Shannon sampling theorem provides an important guideline as to how much digital data is needed to accurately portray a given analog signal.
If a single piece of digital data is lost or misinterpreted, in some systems only a small error may result, while in other systems the meaning of large blocks of related data can completely change. For example, a single-bit error in audio data stored directly as linear pulse-code modulation causes, at worst, a single audible click. But when using audio compression to save storage space and transmission time, a single bit error may cause a much larger disruption.
Because of the cliff effect, it can be difficult for users to tell if a particular system is right on the edge of failure, or if it can tolerate much more noise before failing. Digital fragility can be reduced by designing a digital system for robustness. For example, a parity bit or other error management method can be inserted into the signal path. These schemes help the system detect errors, and then either correct the errors, or request retransmission of the data.