This course gives a fundamental concept in electronics: Semiconductor Materials and PN Junction, Forward biased, reverse biased, and I-V relationship. Diode and Zener Diode, BJT and FET Circuits; design using ideal operational amplifiers, feedback, frequency response, biasing; current sources and mirrors, small-signal analysis, design of operational amplifiers.
This course introduces students to the basic components of electronics: Diode circuits and models – Half and full-wave rectifiers, transistors BJT and FET configurations, selection of Q-point (active operating point) for dc biasing. Bode plot and frequency response. Power amplifiers and amplifier classes. And make student covers the basic operation and some common applications.
Course learning Outcomes
At the end of this course, the students are expected to be able to understand the fundamentals of electronics within the field of electrical engineering. After that, the student will be able to deal with BJT and FET transistor circuits and models and solve circuit which has a BJT and FET transistor. Also, the students are expected to be able know how to use and analyze operational amplifiers and amplifiers classes.
Course contents details Semiconductor Materials
Semiconductors and semiconductor technology forms the basis of most of the electronics industry these days. Transistors, diodes, integrated circuits and many more devices all have semiconductor technology in common. As a result of the enormous degree of flexibility that semiconductor technology provides, it has enabled electronics to take over many areas of daily life, that fifty years ago could not have been conceived.
Conductors and Non-Conductor
In terms of electricity there are two main classes of material: namely: conductors and non-conductors (or insulators). From their names it can be gathered that conductors will conduct electricity freely, whereas non-conductors act as insulators preventing the flow of an electric current.
An electric current is made up of the flow of electrons. This means that for a current to flow, the electrons must be able to move freely within the material. In some materials electrons are moving freely around the lattice, not particularly attached to a given electron. At any instance electrons are moving freely but randomly. By placing a potential difference across the conductor, the electrons can be made to drift in one direction and this constitutes an electric current. Metals are all conductors of electricity, and a number of other substances also conduct it to varying degrees.
Other substances do not have electrons moving freely around the lattice. Electrons are firmly held within their molecules and cannot escape easily. Accordingly, when a potential is placed across the substance very few electrons will move and very little or no current will flow. These substances are called non-conductors or insulators. They include most plastics, ceramics and many naturally occurring substances like wood.
As the name suggests a semiconductor is neither a true conductor nor an insulator, but half way between. A number of materials exhibit this property, and they include germanium, silicon, gallium arsenide, and a variety of other substances.
To understand how it acts as a semiconductor it is necessary to first look at the atomic structure of pure silicon, a good insulator. It consists of a nucleus with three rings or orbits containing electrons, each of which has a negative charge. The nucleus consists of neutrons that are neutral and have no charge, and protons that have a positive charge. In the atom there are the same number of protons and electrons so the whole atom has no overall charge.
The electrons are arranged in rings with strict numbers of electrons. The first ring can only contain two, and the second has eight. The third and outer ring has four. The electrons in the outer shell are shared with those from adjacent atoms to make up a crystal lattice. When this happens there are no free electrons in the lattice, making silicon a good insulator. A similar picture can be seen for germanium. It has two electrons in the inner most orbit, eight in the next, 18 in the third, and four in the outer one. Again, it shares its electrons with those from adjacent atoms to make a crystal lattice without any free electrons.
We have two types of Semiconductors, N-type and P-type.
Diodes are one of the simplest, but most useful of all semiconductor devices. Many types of diode are used for a wide range of applications. Rectifier diodes are a vital component in power supplies where they are used to convert AC mains (line) voltage to DC. Zener diodes are used for voltage stabilization, preventing unwanted variations in DC supplies within a circuit, and to supply accurate reference voltages for many circuits. Diodes can also be used to prevent disastrous damage to battery powered equipment when batteries are connected in the wrong polarity.
Diodes are made from semiconductor materials, mainly silicon, with various compounds (combinations of more than one element) and metals added depending on the function of the diode. Early types of semiconductor diodes were made from Selenium and Germanium, but these diode types have been almost totally replaced by more modern silicon designs.
The operation of diodes can be described by a special graph called a characteristic curve (I/V characteristic). This graph shows the relationship between the actual currents and voltages associated with the different terminals of the device. An understanding of these graphs helps in understanding how the device operates.
There are a lot of application for diode such as: half-wave rectifier, full-wave bridge rectifier, reverse protection diode and Lighting.
Transistors make our electronics world go ‘round. They’re critical as a control source in just about every modern circuit. Sometimes you see them, but more-often-than-not they’re hidden deep within the die of an integrated circuit.
Transistors are three terminal active devices made from different semiconductor materials that can act as either an insulator or a conductor by the application of a small signal voltage. The transistor’s ability to change between these two states enables it to have two basic functions: “switching” (digital electronics) or “amplification” (analogue electronics).
We have two types of transistors: BJT and MOSFET(FET)
The areas of operation for a transistor switch are known as the Saturation Region and the Cut-off Region. This means then that we can ignore the operating Q-point biasing and voltage divider circuitry required for amplification, and use the transistor as a switch by driving it back and forth between its “fully-OFF” (cut-off) and “fully-ON” (saturation) regions as shown below.
Bode Response: In electrical engineering and control theory, a Bode plot is a graph of the frequency response of a system. It is usually a combination of a Bode magnitude plot, expressing the magnitude (usually in decibels) of the frequency response, and a Bode phase plot, expressing the phase shift.
Amplifiers are designated by different classes of operation such as class “A”, class “B”, class “C”, class “AB”, etc. These different amplifier classes range from a near linear output but with low efficiency to a non-linear output but with a high efficiency.
No one class of operation is “better” or “worse” than any other class with the type of operation being determined by the use of the amplifying circuit. There are typical maximum conversion efficiencies for the various types or class of amplifier, with the most commonly used being:
- Class A Amplifier – has low efficiency of less than 40% but good signal reproduction and linearity.
- Class B Amplifier – is twice as efficient as class A amplifiers with a maximum theoretical efficiency of about 70% because the amplifying device only conducts (and uses power) for half of the input signal.
- Class AB Amplifier – has an efficiency rating between that of Class A and Class B but poorer signal reproduction than Class A amplifiers.
- Class C Amplifier – is the most efficient amplifier class but distortion is very high as only a small portion of the input signal is amplified therefore the output signal bears very little resemblance to the input signal. Class C amplifiers have the worst signal reproduction.
In this course we introduced basic concepts of Semiconductors and how to use it to build Diodes and Transistors, we have an idea about Q-point (active operating point) for Transistors. Finally, we gave a basic concept for Amplifier and Amplifier classes.