DEFINITION OF LOGIC GATES
WEEK: 5
CLASS: SS 2
SUBJECT: COMPUTER SCIENCE TOPIC: LOGIC CIRCUITS I
CONTENT:(i) Definition of logic gate (b) Types of logic gates AND, NOT, OR (c) Symbols of each logic gate: (d) Input/output signals for AND, NOT and OR gates.
Sub-Topic 1: DEFINITION OF LOGIC GATES
DEFINITION OF LOGIC GATES
A logic gate is a device that performs a logical operation on one or more inputs and produces a single output. The most common logic gates are AND, OR, and NOT gates. These logic gates can be combined to create complex logic circuits that perform sophisticated operations. In digital electronics, these logic gates are implemented using transistors, diodes, or other electronic components. In addition, logic gates can also be implemented using optical or mechanical means.
Logic gates are the building blocks of digital circuits and form the basis for modern computer systems. Without logic gates, communication and information processing would not be possible
Some examples of real-world applications of logic gates include computer processors, memory devices, and programmable logic controllers. Logic gates are also used in many industrial and manufacturing processes for control and automation.
Overall, logic gates are fundamental components in the field of electronics and play a crucial role in modern technology.
Write five multiple-choice questions with one correct answer and three wrong answers on the topic of logic gates
Logic gates are primarily implemented using diodes or transistors acting as electronic switches, but can also be constructed using electromagnetic relays (relay logic), fluidic logic, pneumatic logic, optics, molecules, or even mechanical elements. With amplification, logic gates can be cascaded in the same way that Boolean functions can be composed, allowing the construction of a physical model of all of Boolean logic, and therefore, all of the algorithms and mathematics that can be described with Boolean logic.
Logic circuits include such devices as multiplexers, registers, arithmetic logic units (ALUs), and computer memory, all the way up through complete microprocessors, which may contain more than 100 million gates. In practice, the gates are made from field-effect transistors (FETs), particularly MOSFETs (metal–oxide–semiconductor field-effect transistors).
A logic gate is an electronic device that makes decisions based on the different combinations of digital signals present on its inputs.
It is a logical circuit device in a computer, having one output channel and one or more input channels, which gives signal only when specific input conditions are met.
EVALUATION:
- What is a Logic gate?
- State three (3) examples of a logic
Sub-Topic 2: TYPES OF LOGIC GATES
There are three basic logic gates from which others can be constructed. These are;
- ‘NOT’ gate
- ‘AND’ gate
- ‘OR’ gate
In logic diagrams, gates are represented by symbols. Inputs and output signals are represented with arrow lines having labels.
The ‘NOT’ Gate: The ‘NOT’ gate is the most basic of all the logic gates and is sometimes referred to as an inverting buffer or simply a digital inverter. This gate accepts a single input and brings out the negative of its input as output. That is it inverts its input signal as output. I.e. if its input is 0, output will be 1, and if its output is 0 it means input will be 1. Or true= false and false =true.
The ‘NOT’ gate accepts only one input signal.
Truth Table for ‘NOT’ gate
| INPUT (A) | OUTPUT (A) |
| 1 | 0 |
| 0 | 1 |
The Boolean expression is A=A
The overline ( ) over the expression signify the NOT
The ‘AND’ Gate: Unlike the ‘NOT’ gate, the ‘AND’ gate accepts only one two inputs signals and bring out one output signal. Hence there are two signal lines.
It is a logic circuit, used in computers that produce a high voltage signal as output if its two inputs carry a high voltage; otherwise it produces a low voltage output if any of its input is low.
Truth Table for ‘AND’ gate
| INPUT (A) | INPUT (B) | OUTPUT (Q) |
| 1 | 1 | 1 |
| 1 | 0 | 0 |
| 0 | 1 | 0 |
| 0 | 0 | 0 |
Two inputs AND gate.
The Boolean expression is A.B=Q
The period (.) in the expression stands for multiplication
The ‘OR’ Gate: This is a logic circuit used in computers, that gives a high voltage output if all or one of its input carries a high voltage, and a low voltage output if all or one of its input carries a low voltage. The ‘OR’ gate also accepts two inputs.
Truth Table of ‘OR’ Gate
| INPUT (A) | INPUT (B) | OUTPUT (Q) |
| 1 | 1 | 1 |
| 1 | 0 | 1 |
| 0 | 1 | 1 |
| 0 | 0 | 0 |
Two inputs OR gate.
The Boolean expression is A+B=Q
The plus used in the expression stands for addition.
EVALUATION:
1.Sketch the truth table of a ‘AND’ gate.
Sub-Topic 3: SYMBOLS OF LOGIC GATES:
AND GATE
OR GATE
‘NOT’ GATE
Sub-Topic 4: USES OF LOGIC Gate
Logic gates are used in digital circuits, such as computer processors and memory chips. They perform Boolean logic operations on input signals to produce an output signal
Some common logic gate functions include AND, OR, NOT, NAND, NOR, and XOR. These gates can also be combined to create more complex operations. Logic gates are also used in many other electronic devices, such as cell phones and televisions. They play a crucial role in modern technology and computing.
Write five multiple-choice questions with one correct answer and three wrong answers on “USES OF LOGIC GATES “.
Logic Gates are used for the following;
- They are used in integrated circuits
- They are used in functioning of transistors, resistors and capacitors
- They are used in making comparators
- They are used in producing high speed CPU’s
- They are used as elemental building blocks for devices where signals must be selected or combined in a controlled form. This is obvious in telephone switching, satellite transmission and digital computer operations.
- They are used in making micro-
- They are used in making amplifiers, and oscillator
- They are used in vacuum tubes
- They are used in constructing alarms used in cars and
EVALUATION:
- State 5 uses of logic gates
GENERAL EVALUATION:
- Define the term logic
- Sketch the symbol of three (3) basic logic gates
- State five (5) uses of the logic
READING ASSIGNMENT:
Students are expected to read ‘Logic gate II’ of Handbook on Computer studies for SS2.
WEEKEND ASSIGNMENT:
- Sketch all the symbols and truth tables of the three basic logic gates and explain them in an exercise book.
[HDquiz quiz = “823”]
