Logic Gates
INTRODUCTION:
In this instructables, I will teach about Logic Gates, Truth tables of Logic Gates, Verification of Truth tables of Logic Gates, Symbols and Boolean expressions of various Logic Gates. I will also tell you how you can get (purchase) these logic gates to design digital circuits (for examples - Full adder, Full subtractor, Flip Flops, Shift Registers and Counters etc.) or verify their truth tables. So Let's get started!
Logic Gates:
Logic gates are the building blocks of any digital circuit such as computer, calculator, adder and subtractor etc. It is an electronic circuit having one or more than one input and only one output. The relationship between the input and the output is based on a certain logic. Based on this, logic gates are named as AND gate, OR gate, NOT gate etc.
Types of Logic Gates
In digital electronics (D.E.) or Digital system design (D.S.D.) logic gates are classified into three categories. These three categories are followings-
- Basic Gates (Basic Logic Gates)
- Universal Gates (Universal Logic Gates)
- Special Gates (Special Logic Gates)
Supplies
Electronic Components
https://quartzcomponents.com
- Passive Electronic Components
Resistors
- 1K
https://quartzcomponents.com/products/1k-ohm-1-4-w...
LED
- LED (RED)
https://quartzcomponents.com/products/red-5mm-led?...
- Active Electronic Components
Logic Gate ICs (TTL Family of Logic gates)
- SN74HC32N ( Quad 2-Input OR Gates)
https://quartzcomponents.com/products/74ls32-quad-...
- SN74HC08N (Quad 2-Input AND Gates)
- SN74HC04N (Hex 1-Input NOT Gates)
https://quartzcomponents.com/products/74ls04-hex-i...
- SN74HC02N (Quad 2-Iput NOR Gates)
https://quartzcomponents.com/products/cd4001-quad-...
- SN74HC00N (Quad 2-Input NAND Gates)
https://quartzcomponents.com/products/74hc00-nand-...
- SN74LS86N (Quad 2-Input EX-OR Gates)
https://quartzcomponents.com/products/74hc86-quad-...
Bread Board
https://quartzcomponents.com/products/colored-brea...
Jumper Wires
https://quartzcomponents.com/products/65pcs-breadb...
2 Positions DIP Switch
https://quartzcomponents.com/products/dip-switch-2...
PCB
BASIC GATES (OR, AND, NOT)
Basic Logic Gates
There are only three Basic logic Gates in Digital Electronics. These are OR Gate, AND Gate and NOT Gate. These Logic Gates are so called the Basic Gates because they form the Base of the Digital Electronics. So first of all let's discuss about OR Gate.
OR Gate
OR gate has two and more than two inputs and only a single output. OR gate performs OR Logical operation on its inputs and provides the result on its output. The Logical symbol and Boolean expression of OR Gate has been given in Image-1.
Boolean Expression of two, three and four input OR Gate are
Y = A+B (Read as "Y is equal to A OR B")
Y = A+B+C (Read as "Y is equal to A OR B OR C")
Y = A+B+C+D (Read as "Y is equal to A OR B OR C OR D")
AND Gate
AND gate has two and more than two inputs and only a single output. AND gate performs AND Logical operation on its inputs and provides the result on its output. The Logical symbol and Boolean expression of AND Gate has been given in Image-2.
Boolean Expression of two, three and four input AND Gate are
Y = A.B (Read as "Y is equal to A AND B")
Y = A.B.C ("Read as Y is equal to A AND B AND C")
Y = A.B.C.D ("Read as Y is equal to A AND B AND C AND D")
NOT Gate
NOT Gate is a little bit different from above two gates (OR and AND). NOT Gate has only a single input and a single output. Logical symbol and Boolean expression of NOT Gate has been given in Image-3. The NOT Gate is also known as an Inverter or Inverter Gate because its output is invert or complement of its input.
Boolean Expression For NOT Gate is
Y = ~A (Read as "Y is not equal to A" or "Y is equal to complement of A")
Universal Logic Gates (NOR and NAND)
Universal Logic Gates
There are only two Universal Logic Gates in Digital Electronics and they are NOR (OR + NOT) and NAND( AND + NOT). The universal gates can me designed using basic gates (OR, AND, NOT). These gates are so called universal Logic Gate because any digital circuit (Simple or Complex) can be created using only these two gates
Types of Universal Logic Gates-
- NOR Gate
- NAND Gate
NOR Gate
NOR Gate has two or more than two inputs and a single output. Basically NOR gate is a combination of OR Gate and NOT Gate. When the output of an OR Gate is given to the input of an NOT gate Then this whole system of basic gates is called a NOR Gate. Symbol of NOR Gate has been given in Image-1. We can represent a NOR Gate by two symbols-
- By combining an OR Gate and a NOT Gate together.
- By using the standard symbol of NOR Gate. In standard symbol of NOR gate, we basically place a bubble on the output of OR Gate like shown in Image-1
Boolean expression of NOR Gate
Y = ~(A+B) {Read as" Y is not equal to A OR B"}
Truth Table
Truth table of NOR Gate has been given in Image-1.
NAND Gate
NAND Gate has two and more than two input terminals and only a single output terminal. NAND Gate is combination of AND and NOT basic Gates. When the output of AND Gate is given to the input of an NOT Gate then this whole combination works as an NAND Gate. Symbol, Boolean expression and truth table of NAND Gate has been shown in Image-2.
Boolean expression of NAND Gate
Y = ~(A.B) { Read as " Y is not equal to A AND B}
Similarly NOR Gate we can represent NAND Gate by combining an AND Gate and an NOT Gate together or By standard symbol of NAND Gate. In standard symbol of NAND Gate, Put a bubble mark at the output of an AND Gate as shown in Image-2.
Special Logic Gates (EX-OR and EX-NOR)
Special Gates or Special Logic Gates:
There are two special logic Gates in Digital Electronics. They are EX-OR Gate (Exclusive OR Gate) and EX-NOR Gate (Exclusive NOR Gate). These Logic Gates are so called special gates because their operations on the inputs are a little bit special in comparison to Basic and Universal Logic Gates.
EX-OR (Exclusive OR) Gate
EX-OR Gate has two or more than two input terminals and only a single output terminal. Symbol and Truth table of EX-OR Gate has been given in Image-1.
Boolean Expression of EX-OR Gate is following
Y = A ⊕ B (Read as "Y is equal to A EX-OR B")
EX-NOR (Exclusive NOR) Gate
EX-NOR Gate has two or more than two input terminals and only a single output terminal. We can represent an EX-NOR Gate by connecting an NOT Gate at the output of EX-OR Gate. Truth table and Logic symbol of EX-NOR Gate has been given in Image-2
Boolean Expression of EX-NOR Gate is
Y = ~( A ⊕ B) { Read as "Y is not equal to A EX-OR B")
Pictures of My Work
