Lecture Notes in Analog Electronics

When one holds his mobile phone or is looking at the television set one sees an electronic device. If one opens the device, however, one will see a number of square shaped chips resembling centipede insects properly ordered on a board. What cannot be seen is the internal structure of the chips. So, here we are. It is our intention in this book to open to the reader the magic miniature world of electronics.

This chapter will explain some basic physical principles related to the mechanism of electric current conduction in metals, semiconductors, and vacuum. The knowledge in this area will be useful to the reader to understand the functionality of electronic components discussed in this book. The scope of the exposed substance and the manner of exposure are adjusted to that goal.

Junctions of many kinds may be encountered in electronic components. The most frequent are the metal–semiconductor and the p-n junctions. Heterojunctions where semiconductors having different properties are brought together are also frequent. In this chapter we will try to deliver the basic knowledge needed for understanding the functionality of these structures. That will allow for introducing the story of the first electronic component, the diode. Various types of diodes will be considered. In addition, a completely new phenomenon will be introduced, the nonlinear capacitance. It is inherent to the p-n junction and the diode and is of crucial importance for understanding the properties, behavior, and application of most electronic components, not only diodes.

From this chapter, we are visiting the so-called active electronic components. That means that one can use these components for signal amplification. The bipolar junction transistor was the first discovered among them and became a promoter of the new technology of semiconductor electronics. Here we will try to give as complete an information as possible on the structure, functionally, properties, modeling, parameters, and limitations of its use.

Here is the second active device in the series. Its fundamental difference with respect to the BJT is the fact that the transistor effect is achieved by an electric field which is controlling the output current. So, we introduce the first component of the family of field effect transistors (FET). Since there is no need for a current to control the output, these components exhibit very high resistance between the input terminals. On the other side, while with reduced transconductance compared with BJT, they exhibit high output resistance also. We will deliver here all the necessary information to basically understand the functionality of the new component and, of course, to its applicability. Note the part of Appendix 1B where some SPICE simulations are given with the aim to clarify some aspects related to the nonlinearity and dynamic behavior of this component, please.

Unlike JFET, where the gate was coupled to the channel via p–n junction, the other category of field-effect transistors has an insulated gate. Silicon oxide (SiO₂) is used as insulation. Hence the name IGFET (insulated gate field-effect transistor). It is easy to conclude that the gate current of such a component is even lower than in a JFET, which is a great advantage of this category of transistors. Since IGFET can be made of very small dimensions and since such components are easily isolated in integrated circuits, they became by far the dominant component in modern digital electronics. They are also very widely used as parts of analog circuits and, recently, they are frequently implemented as discrete power components. In these transistors, the gate was first made of metal (aluminium) so that a sandwich is formed: metal–oxide–semiconductor. This is how the alternate name of these components came. MOSFET from metal–oxide–semiconductor FET. Recently, highly doped polysilicon or silicon compounds (silicides) have been used to make gates. The name MOS transistor has remained independent of advances in technology.

Here we complete the study of semiconductor components intended to be used as amplifying devices as well as part of digital logic circuits. The component we are visiting is named MESFET. It is a field effect device which mainly resembles the JFET but has no junction. Instead, a Schottky diode is formed in the place of the JFET’s gate. In that, the component resembles the MOSFET but there is no oxide between the gate metallization and the substrate. The main benefits of this arrangement is related to the reduction of the capacitances and the transit time of the main carriers from the source to the drain. The latter is achieved by rising the electrostatic field acting longitudinal to the channel so that the carriers run with saturated velocity (equal to the thermal velocity). Furthermore, if a material exhibiting higher thermal velocity of the carriers is implemented (e.g., GaAs) further rise of the upper cut-off frequency may be achieved. It is worth mentioning here that the current in a MESFET is established deep in the semiconductor body so avoiding the surface which is known as the important source of electronic noise.

Until now, on several occasions we have mentioned that the light affects the electrical properties of semiconductors. It was also mentioned that during recombination in a semiconductor, photons—quants of light—are released. It should be noted here that light usually refers to electromagnetic radiation that is detected by the human eye. In the following text, however, light will mean radiation independent of wavelength. Thanks to the aforementioned light absorption and emission phenomena, a number of semiconductor components have been developed that exhibit specific properties. They can be divided into two basic categories: those that absorb light—photodetectors and those that emit light—light sources (or light emitting devices, LED). By combining a light source and a photodetector into a single component, an element based on light coupling is obtained, which is known as an optocoupler or optoisolator. As it usually happens, a niche application of a component, during time, becomes its predominant. That we witness in both the photodetectors and LEDs. The former became a solar cell on which the future of the world’s energy system is based. The latter became a substitution to the incandescent and the noble-gas-filled lamps. In that way, optoelectronic devices affect not only electronic sensory, control, and telecommunication systems but also the energy supply and light sources all over the world. So, one may say the optoelectronic components became ubiquitous hence the attention devoted to them in this chapter. We will try here to cover most of the topics related to optoelectronics starting with basic physics, over component construction characterization and modeling, ending with some simple applications which illustrate their functionality.

The interaction of the magnetic field and moving charge carriers i.e., electric current carriers is known for centuries now. The most impressive experience in that was probably the one of Ohm when experimenting with wires carrying current. Namely, at the time there were no quality constant voltage sources and proper ampere meters. He was forced to measure the force exercising the wires one to another in order to deduce the values of the current in a very indirect manner. We, of course, nowadays appreciate his fantastic intuition to discover one of the most important laws in nature. It was Lorenz, however, the one who quantified the force imposed by a magnetic field on a charge carrier and to open the era of another kind of electromagnetic sensor. Namely, one may now control the movement of the carriers in a semiconductor being non-magnetic material and so create proper transducers. The interaction of the magnetic field and the charge carriers in the semiconductor is far from being simple despite the validity of the Lorenz force expression. Namely, due to mutual interaction of the carriers, the scattering on the atoms of the crystal lattice, recombination and generation, and even the surface effects in semiconductors, additional effects should be considered in order to fully characterize the ongoing events in a semiconductor exposed to a magnetic field. To get a general picture, on earth at the equator an average induction of about 0.035 mT may be measured. However, if the distance to earth is large or if variations in the earth's magnetic field are to be detected, a resolution of 0.5 gamma (1 gamma = 1 nT) would be required. On the other side magnetic induction in motors reaches several tens of Tesla so one may imagine the range of sensitivity that is expected from this kind of sensors. Note also that the earth field is omnipresent and has to be compensated in cases when fable magnetic fields of artificial origin are to be measured. Finally, if integrated, the magnetic sensor would normally be encapsulated in plastic or ceramic housing. If so, however, the rest of the integrated circuit would become exposed to the same magnetic field and its functionality would be damaged. In such cases, a special ferromagnetic (iron) covering is used to protect the rest of the IC. In this chapter, we will briefly describe semiconductor components acting as magnetic sensors where one out of four effects dominates. These are Hall effect, magnetoresistivity, magnetoconcentration, and the effect of bending the current lines. Proper components and their characteristics will be described including the main parameters governing their properties. A very rudimentary example will be given for the implementation of one of them.

How semiconductor (discrete and integrated electronic) components are made is of interest not only to satisfy the curiosity of the reader but also to enable an understanding of their functionality and properties. In this Appendix, we will first go through the main processes which enable obtaining the material (silicon) which is mainly the base of the semiconductor technology. Processes implemented to produce p–n junctions and consequently, all electronic components will be studied next. That will allow introduction of integrated circuits which nowadays are becoming the moving force of the human society. Bipolar and MOS integrated circuits will be studied first. That will be followed by the non-semiconductor technologies of thick- and thin-film integrated circuits which in fact use semiconductor chips to complete the circuit function. Actions needed to produce an integrated circuit in all these will be studied i.e., several technological suits will be followed. Whenever necessary, properties of the resulting circuits will be given. The reader should be aware that this is a technology characterized by a very fast progress so that what we give here is only a rudimentary glimpse of the subject aiming to explain the basic terms and to encourage the reader to go further in the study.

In this Appendix, a short set of solved problems will be given. Mainly, it is devoted to quantifying the physical and electrical quantities that are encountered within this chapter. It consists of several parts. First, we illustrate some properties of the semiconductor materials from the electrical current conduction point of view. Then we go for the p-n junction exemplifying the DC and dynamic properties of it. Follows a set of diode circuits. Here, one has to have in mind that DC regimes in electronic circuits containing diodes as prime components will be not studied anywhere more in LNAE so that some additional attention was devoted to them. We finish with examples related to transistors including BJT, JFET and MOSFET.

All electronic components are nonlinear, i.e., the currents are nonlinear functions of the voltages brought at their terminal. That stands not only for their static (very low frequency) characteristics but also for their dynamic ones since the components are surrounded by many capacitances some of them being related to the functionality of the component (junction capacitance, diffusion capacitance, MOS capacitance) and other related to the parasitic connections with the surroundings be it on the semiconductor pellet or on the printed circuit board.

The number of different types of diodes, bipolar transistors, field-effect transistors as well as specific components such as optoelectronics and others is very large. For each type of component, thousands of variants can be found on the market, each adapted to a specific application. Their characteristics are related to the way they are designed and manufactured. Therefore, there is a need to give different codes to different semiconductor components in order to differentiate them from each other in the market. It was usual for the manufacturers to name the components they produced, and the appropriate nomenclature came from that. Soon, however, standard industry codes began to be used. In this way, not only the standardization of the markings, but also the standardization of the components that carry those markings is enabled, independently of the manufacturing company or even the country in which they were produced. In this chapter, we will follow one of standards we find to be the most popular one.