Electronics and System Components Course PDF

Faculté des sciences Département Informatique Course of Electronics and system Electronics and system components components Dr. ABDERREZAK Mohamed Zaki 2024-2025 ...

Faculté des sciences Département Informatique Course of Electronics and system Electronics and system components components Dr. ABDERREZAK Mohamed Zaki 2024-2025  Chapter 1. Definitions And Generalities Objective of Chapter. The objective of this chapter is to define current and understand the difference between direct current and alternating current. Introduction to the electrical signal and define his types. Understand the steps of convert an analog signal to a digital signal. I. Electric current. Electric current is the free movement of electrons from one atom to another in the same direction. This movement, called flow of electrons is referred to as current and is designated by the symbol (i), the unit of measure the electric current is the ampere (A). In a conductor (for example copper), there are several free electrons that move from one atom to another Figure 1.a. If we connect a power supply and apply a voltage, the electrons will flow from the negative terminal to the positive terminal, passing through the copper wire. We notice that the electrons jump from one atom to another to reach the positive terminal Figure 1.b. This flow of electrons called electric current. Figure 1.a. Figure 1.b. Figure 1. flow of electron in copper wire The direction of electron movement determine two types of electric current: Direct Current (DC) and Alternating Current (AC). -1-  Chapter 1. Definitions And Generalities II. Current types. There are mainly two types of current, and they are direct current (DC) and alternating current (AC). II.1. Direct Current (DC). Is an electric current in which the movement of electrons occurs continuously in one direction from negative to positive (Figure2). We know the direct current (DC) of the car like the 12 volt or the 5 volt USB socket for the cell phone. Figure2. Direct current II.2. Alternating Current (AC). Is a type of electrical current in which the flow of electric charge (electrons) periodically reverses direction (Figure3). Our entire household runs on alternating current (AC) for example refrigerator run at 230 V. Figure 3 Alternating current -2-  Chapter 1. Definitions And Generalities II.3. Differences between AC and DC. The major differences between Alternating Current and Direct Current are given in the table below: Alternating Current Direct Current AC is easy to be transferred over longer DC cannot be transferred over a very long distances – even between two cities – without distance. It loses electric power. much energy loss. The rotating magnets cause the change in The steady magnetism makes DC flow in a direction of electric flow. single direction. The frequency of AC is dependent upon the DC has no frequency or zero frequency. country. But, generally, the frequency is 50 Hz or 60 Hz. In AC the flow of current changes its It flows in a single direction steadily direction forward and backward periodically. Electrons in AC keep changing their Electrons only move in one direction directions – backward and forward. –forward. Figure4. Difference between AC and DC Figure.. shows the difference between AC and DC. The green curve (which represents direct current) has constant values that do not change, unlike the orange curve which varies over time this is Alternating Current. -3-  Chapter 1. Definitions And Generalities III. Electric signal. An electric signal is a transmission of electrical energy that carries information. It can take the form of a varying voltage or current that conveys data or instructions through electrical circuits. Electric signals are used in many systems, such as communication devices, computers, and transmit information between components. For example Transmission of a photo from one person to another via mobile network (Figure…). The picture is represented by a set of binary codes 0 and 1 (figure5.1), in the telephone it has an electronic card which will transform this code into an electrical signal (this photo then passed from the digital part to the analog part (signal electrical) figure 5.2. The antenna of the telephone will transform the electronic signal into an electromagnetic wave which propagates in the air to reach the nearest relay antenna (also called base station) figure 5.3. To level the wave and transform it again into an electrical signal which will be transmitted over a long distance by electric or optical fiber cables to the another antenna figure 5.4-5 This antenna will transform the electrical signal into an electromagnetic wave figure 5.6 This wave be transmitted to the antenna of the smartphone which will transform into an electrical signal, and then the smartphone will translate the analog signal into a digital signal (that is to say a binary code) figure 5.7which will be decoded by the electronic card to display the result on the screen figure5.8. -1- -2- -3- -4- -8- -7- -6- -5- Figure 5. Transmission via mobile network -4-  Chapter 1. Definitions And Generalities Remark: The primary role of electric signals is transmit information and energy. III.1. Types of signal. Signals can be classified into different types based on their characteristics. The two primary types of signals are analog and digital. III.1.1. Analog signal: Analog signals are continuous and vary smoothly over time (figure6). They can take any value within a given range. For example, sound waves, and temperature readings. Figure 6. Analog signal III.2. Digital signal: Digital signals are discrete and non-continuous (figure 7), consisting of binary values (0s and 1s). They have specific steps in both time and amplitude. For example, Signals in computers, digital watches, and most modern communication systems. Figure 7. Digital signal VI. Analog-to-digital conversion. The transition from analog to digital involves converting continuous analog signals into discrete digital signals, a process known as analog-to-digital conversion (ADC). This is essential in many modern systems, such as computers, digital communication, and digital audio, where signals need to be represented in binary form (0s and 1s) for processing, storage, and transmission, see figure 8. -5-  Chapter 1. Definitions And Generalities Figure 8. Analog-to-digital conversion. IV.1.The Analog-to-Digital Conversion (ADC) Process: 1. Sampling:  Definition: The process of measuring the analog signal's value at regular intervals (called sampling points) and converting it into discrete time values.  Sampling Rate: Determines how often the analog signal is measured. It is measured in samples per second or Hertz (Hz).  Nyquist-Shannon Sampling Theorem: To accurately convert an analog signal to digital, the sampling rate should be at least twice the highest frequency in the analog signal (Fe ≥ 2 F). Example: If you're converting a human voice (Figure 9) with a frequency range of up to 3 kHz, the sampling rate should be at least: Figure 9. Example for Sampling step Fe = 2 * F Fe = 2*3 = 6 kHz (6000 samples per second). We must find how many points in our signal: -6-  Chapter 1. Definitions And Generalities 6000 samples 1 second X = 15 samples X 2,5 x10-3 s In our signal (2,5 ms) we have 15 samples, to find the sampling frequency we use the 1 1 1 formula 𝑇 = 𝐹 so 𝑇𝑒 = 𝐹 𝑇𝑒 = 6000 = 0.16 𝑚𝑠 , interval between each samples 𝑒 is 0.16ms (figure 10). Figure 10. sampling of signal 2. Quantization:  Definition: The process of mapping the sampled signal's continuous amplitude values into a finite set of discrete levels.  Quantization Levels: These levels are the possible digital values assigned to the analog signal's amplitude. The number of levels is determined by 𝑁 = 2𝑄 / Q : bit of qantization defined by constroctor of ADC. For example : Q=2bit , N= 4, -7-  Chapter 1. Definitions And Generalities Figure 11. quantization of the signal 3. coding:  Definition: After quantization, each sampled value is converted into its binary form (a series of 0s and 1s) for storage or processing in digital form.  Result: The original continuous analog signal is now represented as a discrete digital signal consisting of a sequence of binary values (figure 12). Figure 13. Digital signal. REMARK. According to Shannon's theorem, the sampling frequency must be greater than or equal to 2 times the maximum frequency of the signal, and the greater the number of bits, the closer the analog signal is to the analog signal (figure14). -8-  Chapter 1. Definitions And Generalities Figure 13. Difference between coding in 3 bits and 4 bits. -9-