Important facts about logic gates

Updated: Aug 9, 2023

A #logicgate is an electronic circuit that accepts binary inputs and produces a binary output. They are named after the Boolean functions they perform on the inputs. A logic gate can have multiple inputs but has only one output. Here are some salient facts about these logic gates,

Transistors are used in the electronic circuit that internally constitutes a logic gate. The most commonly used transistor type in these circuits is the CMOS type. CMOS transistors have an advantage over other transistor types in the reduction of power consumption.
The input-output relation of a logic gate is represented as a truth table.
Universal logic gates, when used independently in a circuit, can reproduce the Boolean function of other logic gates. This property is called as functional completeness. NAND and NOR are the universal logic gates.
OR, AND, XOR, XNOR and NOT are some of the basic logic gates that can be realized using the universal gates. | Important facts about logic gates |

Important facts about logic gates Truth tables

OR (A.B) gate performs logical OR operation. The output of this Boolean function will be the maximum among the inputs given to the gate. The truth table for an OR gate functions as follows,

Truth Table for OR gate

AND (A+B) gate performs logical AND operation. Here, the minimum value among the inputs given to the gate reflects as the output. The truth table for this gate is as follows,

Truth Table for AND gate

NOT (A') gate performs logical NOT operation. This gate inverts the binary input given to the gate. Hence this gate is also known as an Inverter. Here is the simple truth table of the NOT gate,

Truth Table for NOT gate

XOR ((A.B')+(A'.B) or A ⊕ B) gate performs logical XOR operation. The output of this gate will be high only when only one of the inputs given to the gate is high. The truth table for this gate reads as follows,

Truth Table for XOR gate

XNOR ((A.B)+(A'.B') or (A ⊕ B)' ) performs logical XNOR operation. The output of the gate is high only when both the inputs are the same. The truth table of this gate is the complement of the XOR gate.

Truth Table for XNOR gate

NAND (A.B)' gate is a universal gate and, it performs logical NAND operation. The output of this gate can be high only if at least one of the inputs is low. The truth table is the complement of the AND gate. Hence, the name NAND- NOT AND.

Truth Table for NAND gate

NOR (A+B)' gate is also a universal gate and performs logical NOR operation. The gate outputs high binary values only when both the inputs are low. This gate is the complement of the OR gate. Hence, the name NOR- NOT OR. The truth table for this gate functions as follows,

Truth Table for NOR gate

The buffer (A) gate's output is equal to the value of the input. This gate too can be realized using the universal gates.

Truth Table for the buffer gate

Each of these gates is represented as symbols in the schematic diagrams of a digital circuit. The following table puts forth all the logic gate symbols,

Logic Gate Symbols

The voltage given to achieve off state in a logic gate is zero, while to achieve ON state, the voltage range given to the logic gate must be 3.5 to 5 volts.
The number of inputs a logic gate can have is as many as four inputs. The truth table will vary according to the number of inputs given to the gate.
The logic gates are employed in the adder, multiplexer, and flip-flop circuits. They are also the fundamental elements of intricate circuits like microcontrollers and microprocessors. Thus, logic gates can be considered as the key elements in the world of #digitalelectronics .

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Name- Nagashree R Nadig

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Important facts about logic gates

Important facts about logic gates Truth tables

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