What is a LOGIC GATE
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 seven basic logic gates: AND, OR, XOR, NOT, NAND, NOR, and XNOR.
NOT LOGIC GATE
This gate has one input and one output. The output is high when input is low and vice-versa The diagram is shown below
Inverter or NOT gate
TRUTH TABLE OF NOT GATE
Input | Output |
1 | 0 |
0 | 1 |
AND GATE
This logic gate has two or more inputs and one output. The output is high only when all the inputs are high.
AND gate
TRUTH TABLE OF AND GATE
Input 1 | Input 2 | Output |
0 | 0 | 0 |
0 | 1 | 0 |
1 | 0 | 0 |
1 | 1 | 1 |
OR GATE
OR gate has two or more input and one output. The output is high for any of the input being high.
OR gate
Input 1 | Input 2 | Output |
0 | 0 | 0 |
0 | 1 | 1 |
1 | 0 | 1 |
1 | 1 | 1 |
XOR GATE
The XOR ( exclusive-OR ) gate has two or more inputs and one output. The output is low for the inputs being same and the output is high for the input being different.
XOR gate
TRUTH TABLE OF XOR GATE
Input 1 | Input 2 | Output |
0 | 0 | 0 |
0 | 1 | 1 |
1 | 0 | 1 |
1 | 1 | 0 |
What are the use of Logic gates ?
Logic gates are in fact the building block of digital electronics; they are formed by the combination of transistors (either BJT or MOSFET) to realize some digital operations (like logical OR, AND, INVERT ). Every digital product, like computers, mobile, calculators even digital watches, contain logic gates. The use of logic gates in digital world can be understood better by the following example: the single bit full adder in digital electronics is a logic circuit which perform the logical addition of two single bit binary numbers (a,b,cin) a and b are the the two binary number of single digit (either 1 or 0) and cin is the carry input . say for example a,b,cin= 1,1,1 gave an logical sum output of 1 and a carry of 1 , a,b,cin= 110 gave sum= 0 and carry of 1. Now this adder can be formed by the combination of many gate like by using NAND gates only. or by using XOR , AND ,OR gates and so on. So, in a nutshell, the adder which is of great importance in your computer processor and also in many more applications is basically built from the logic gates.
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