LOGIC GATES/CIRCUITS 1-2 (JS3 NOTES)

 

LOGIC GATES/CIRCUITS  1-2

INTRODUCTION/DEFINITION, TYPES, SYMBOLS AND USES

Objective: At the end of the lesson, the students should be able to:

1. Define logic gates

2. State the types of logic gate

3. Draw logic gates symbols

4.State the uses of logic gates

DEFINITION OF LOGIC GATES

A logic gate is an elementary building block of a digital circuit. Most logic gates have two inputs and one output. At any given moment, every terminal is in one of the two binary conditions low (0) or high (1), represented by different voltage levels.

Types of Standard Single Logic gate

There are three types of standard single logic gates. They are:
1. AND gate
2. OR gate
3. NOT gate

Alternative Logic Gates are:

4. NAND gate

5. NOR gate

1.  AND gate: AND gate will give a high output only if all of the inputs are high. It means multiplication (x). For example if A = 0 and B= 1, A AND B = 0 X 1 = 0

AND GATE SYMBOL

2. OR gate : This is a digital logic gate that gives an output of 1 when any of its inputs are 1, otherwise 0. it means addition (+).For example if A = 1 and B=1, then A OR B = 1+1 = 1

3. NOT gate: This is often called an inverter. A NOT gate is slightly different because it has just one input. It will give a high output if the input is low and vice versa. For example if A = 0, then NOT A = 1 and if A = 1, then NOT  A = 0

4. NAND gate : This is the combination of AND gate and NOT gate. It is the inverse of AND gate.

5. NOR gate : This is the combination of OR gate and NOT gate. It is the inverse of OR gate.

USES OF LOGIC GATES

1. They are used as building blocks of digital electronics hardware

2. They are used for decision making

3. It is used in constructing alarm system.

4. It is used in traffic light control system

5. It is used in light activated burglar system.

6. It is used in safety thermostat.

7. It is used in constructing switches.

8. It is used in car security systems.