Logic Gates

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. The logic state of a terminal can, and generally does, change often, as the circuit processes data. In most logic gates, the low state is approximately zero volts (0 V), while the high state is approximately five volts positive (+5 V).

There are 3 main Logic Gates.

                                                                   1. AND Gate 

The AND gate is a basic digital logic gate that implements logical conjunction. A HIGH output results only if all the inputs to the AND gate are HIGH. If none or not all inputs to the AND gate are HIGH, a LOW output results

                                     

Truth Table of AND Gate

A	B	F
0	0	0
0	1	0
1	0	0
1	1	1

2. OR Gate

The OR gate is a digital logic gate that implements logical disjunction – it behaves according to the truth table to the right. A HIGH output (1) results if one or both the inputs to the gate are HIGH (1). If neither input is high, a LOW output (0) results.

3.NOT Gate

The NOT Gate is a Boolean operator with only one variable that has the value one when the variable is zero and vice versa.

Using above 3 main Logic Gates we can create Combined Logic Gates too.

1. NAND Gate

In digital electronics, a NAND gate is a logic gate which produces an output which is false only if all its inputs are true; thus its output is complement to that of an AND gate. A LOW output results only if all the inputs to the gate are HIGH; if any input is LOW, a HIGH output results

• NOT Gate +AND Gate = NAND Gate

2. NOR Gate

The NOR gate is a digital logic gate that implements logical NOR - it behaves according to the truth table to the right. A HIGH output results if both the inputs to the gate are LOW; if one or both input is HIGH, a LOW output results. NOR is the result of the negation of the OR operator.

          

• NOT Gate +OR Gate =NOR Gate

Truth Table of OR Gate

A	B	F
0	0	0
0	1	0
1	0	0
1	1	1

Truth Table of NOT Gate