Table of contents
Electronics is the science and technique concerning the emission and propagation of electrons in vacuum or in matter; as a science is a branch of physics, in particular of electrology: born as a branch of electrical engineering is now understood as a discipline in itself, and can be defined as “technique of weak currents and high frequency” differing from electrical engineering that is instead “the technique of strong currents and low frequency”.
More specifically, electronics is the set of methodological, theoretical and practical knowledge used for the design and implementation of systems and hardware equipment capable of processing physical quantities in the form of signals containing information, for various types of applications; the achievements of electronics are therefore electronic circuits of processing consisting of electronic components, active and passive, connected by means of wires or conductive paths, usually metal, through which circulate electric currents; this area deals with the electronic engineering.
The first achievements of electronics were radio receiving and transmitting circuits; no doubt Guglielmo Marconi and Nikola Tesla were pioneers, but their first radios had nothing that could not be considered more than an application of electrical engineering to a new problem. The real breakthrough came with the work of British engineer John Ambrose Fleming of University College London, who in 1904 invented the first two-terminal electronic device, the vacuum diode, i.e. the first thermionic valve. Followed shortly (1906) the first three-electrode electronic component by Lee De Forest, the vacuum triode, which also allowed to amplify a signal.
Historically, therefore, electronics came to the fore with the invention of the vacuum triode (L. De Forest, 1908), its application as an amplifier in radio communications (1918) and the industrial manufacture of the first radio receivers (1923). The attention was then focused on vacuum tubes, the protagonists of the applications, and the definition of electronics as a science that studies the motion of the electron in vacuum and the devices that use its properties could seem quite satisfactory. Later, with the evolution of the theory of counter-reaction (H. S. Black, 1934, H. Nyquist, 1938 and H. W. Bode, 1940), which is the foundation of modern methods of control and regulation, and the development of logic circuits (C. E. Shannon, 1938), which led in 1943 to the realization of the first electronic computer (the ENIAC), it became evident the need to configure electronics more for the objectives that it proposes than for the technical means that it employs.
Electronics was then defined as the applied science that aims to enhance man’s senses and intellectual capabilities through tools that process and collect information to control machines and devices or present it for direct use in an appropriate way. This definition has not lost its relevance today, although it has the defect of being necessarily vague about the technical physiognomy of electronics and overestimating its links with cybernetics. A certain imprecision in the definition, however, is linked to the fact that electronics has represented the common matrix of a growing number of relatively independent sectors, which, in interaction with electronics, were evolving their precise role in science or engineering.
After World War I, electronics developed rapidly, especially thanks to the radio, which in that period was its leading application; in circuit theory a milestone was reached in 1927 with the invention of the first reaction circuit, which allowed to achieve with few components a much higher performance, while radio devices were becoming more and more advanced, passing from the first simple homodyne or synchrodyne circuit schemes to more complex heterodyne and superheterodyne schemes, which guaranteed a better separation between radio stations and less noise.
After World War II, an important milestone in the development of electronics coincided with the invention of the transistor by J. Bardeen and W. H. Brattain (1948) and by W. B. Shockley (1949), and with the subsequent development (1957) of manufacturing technologies for semiconductor components, which not only allowed the start of the miniaturization process, but above all considerably increased the reliability of electronic equipment, making possible the realization of the first high-speed computers (around 1958).
Although inconspicuous from the scientific point of view, also the introduction of technologies based on epitaxial growth processes, first improving transistors (1961) and then leading to the realization of integrated circuits (1962), is to be considered an event of extreme importance, because it has allowed to increase considerably the complexity and reliability of circuits, causing a revolution in the division of tasks and design methods, undoubtedly superior to that due to the advent of the transistor. Progress in this field is continuing, while in the study of compound semiconductors there have been grounds for interest with the development of new hyperfrequency devices (Gunn effect devices and IMPATT diodes) and infrared detectors.
The studies on stimulated emission by A. Schawlow, C. H. Townes and N. G. Basov (1959) led to the experimental realization of the first ruby laser by T. H. Maiman (1960) and the subsequent development of increasingly powerful lasers with emission in the visible and infrared.
In the seventies there have been further developments in electronics both from the technological point of view and in applications mainly concerning information processing and telecommunications. Production technology has been increasingly oriented towards reducing the physical size of components (transistors, diodes, etc.) that perform electronic functions.
With microelectronics it is possible to concentrate on a chip even more than one million transistors with the related passive components and circuit connections; in the early nineties chips have performances approaching those of supercomputers for speed, ability to perform vector operations, memory, reliability, etc. and have relatively low costs. At the same time all the software (programming languages, operating systems, etc.) necessary for their operation has been improved.
In the field of telecommunications has developed enormously the network of geostationary satellites, each of which allows the simultaneous intercontinental transmission of several television programs and a few thousand telephone calls; it is also to report the entry into service of telephone switching stations completely electronic.
Very important have been the developments of electro-optics or optoelectronics, a new technology that uses for information processing and communications not only electronic phenomena, but also the coherent light of the laser and optical phenomena in general. The availability of tiny semiconductor lasers, of extremely thin and transparent optical fibers and of new photosensitive materials has allowed the transmission of electrical signals along optical fibers (obtaining, in the field of telecommunications, a transmission capacity greater than that of coaxial cable and a lower attenuation of the signal itself), as well as to realize optical memories with an information density two million times greater than that of a tape or perforated band.
First with transistors and then with integrated circuits, electronics experienced a real boom, which has not yet ended.
Branches of electronics
- Digital electronics
- Analogue electronics
- Circuit design
- Integrated circuits
- Power electronics
- Semiconductor devices
- Embedded systems
- Audio electronics
Solid state electronics
The term “solid state” in electronics generally refers to all semiconductor devices (which differ from all other electronic components and devices in that they have no moving mechanical parts – electromechanical devices). This term derives from the contrast with electronic devices of the past, namely vacuum or gas tubes, in which electrons move in free regions of space.
This field is based on the knowledge derived from solid state physics and allows the development of all those components in which electrons move inside solid materials (such as semiconductors). The name comes from the contrast with vacuum or gas tube electronics, in which electrons move in free regions of space. For the same applications, circuits made with solid-state electronics technology are characterized by much lower voltage and current levels than similar circuits made with electron tubes, which tend to be gradually replaced in various applications. For example, the replacement of cathode ray tube (CRT) screens with liquid crystal display (LCD) screens in television sets has made it possible to build such sets using only solid-state electronic circuits, with great advantages for power consumption and internal voltage levels (in particular, high voltage elements are no longer present).
Solid state electronics is based on the knowledge derived from solid state physics and allows the development of all those components in which electrons move inside solid materials (i.e. semiconductors); such as microprocessors.
For the same applications, circuits realized with solid state electronics technology are characterized by much lower voltage and current levels than similar circuits realized with electronic tubes.
The term power electronics refers to the activities, products and applications that deal with the electronic conversion of electrical energy, i.e. the control with electronic equipment of the transfer of electrical energy between generators and users (loads). It concerns, therefore, the set of devices, systems and techniques necessary to operate, with high energy efficiency, controlled transfers of electrical energy.
The devices that electronically realize this energy control are called power electronic converters (hereinafter referred to as converters) and play the role of electronic interfaces, which act on the electrical quantities supplied by the sources in order to adapt them to the needs of the loads. Converters are classified into DC/DC converters (if they are intended to act as an interface between DC sources and loads), AC/DC converters or rectifiers (if the sources are AC and the loads are DC), DC/AC converters or inverters (if the sources are DC and the loads are AC) and AC/AC converters (if the sources and loads are AC, not necessarily at the same frequency).
A power electronic system is, therefore, made up of one or more converters, the related filtering, control and protection circuits, as well as any transformers (with functions of isolation and adaptation of voltage levels), which allow to operate the desired energy conversion according to the static and dynamic specifications of the sources and loads.
The evolution of this sector has been rapid and accompanied by a constant expansion of the market, this is due to the possibilities offered by solid state devices to control the electrical power no longer in fractions of a second, characteristic of electromechanical components, but in millionths of a second; to this must be added the synergy resulting from the possibility of achieving a direct interface with microelectronics to perform a fully electronic control of electrical powers.
The wide range of powers involved in the applications (from a few Watts up to many MW), the different characteristics of the sources (voltages from a few volts up to hundreds of kV, currents between a few mA and hundreds of kA) and the variety of specific needs of the loads mean that the manufacturing technologies of power converters are very different even within the same class of converters.
The first semiconductor electronic components used for power conversion were diodes and thyristors, in particular SCR (Silicon Controlled Rectifier), RCT (Reverse Conducting Thyristor) and TRIAC (Triode Alternate Current Switch), on which was based the development of solid state rectifier circuits since the fifties and their massive diffusion since the sixties.
In the seventies the power bipolar transistors or BJT (Bipolar Junction Transistor) became established, then joined by the field effect power transistors (Power Mosfet), developed in the eighties, and the insulated gate bipolar transistors or IGBT (Insulated Gate Bipolar Transistor), introduced in the nineties. In power electronics applications all devices are used as electronic switches in order to achieve high efficiency and low power dissipation.
In some high power applications are used GTO thyristors (Gate Turn Off Thyristor) that can withstand voltages of some kV, currents of some kA and be controlled on and off by the gate electrode. It should be emphasized that research, in addition to the development of new semiconductor power components with improved characteristics, aims at an integrated product, in which in addition to the component there are the on/off circuit and the protection circuits.
Even if some of the above mentioned devices (in particular transistors) would allow linear adjustments, similarly to what happens in amplifier circuits, the need to achieve high energy efficiency, i.e. low energy losses in power electronic conversion, requires the use of all electronic components in switching mode, i.e. as switches that assume only the “open” (off) or “closed” (on) states.
In fact, while an electronic component in linear operation is subjected simultaneously to significant voltages and currents and is, therefore, home to a significant power dissipation, a component used in switching mode dissipates a modest power: in the off state the current flowing through it is negligible, while in the on state the voltage drop at its ends is small, on the other hand, most of the power loss is concentrated during the switching between the two states on and off, and is therefore proportional to the number of commutations.