A logic gate is a circuit that can make logical decisions based on the combination of input signals. A logic gate can take more than one input signals and usually provide only one output signal. There are three types of logic gates basic logic gates, universal gates and other gates.
Various types of logic gate include:
- AND Gate
- OR Gate
- NOT Gate
- NANAD Gate
- NOR Gate
- XOR Gate
- XNOR Gate
In this article we will focus on two universal gates i.e NAND and NOR gate.
What are Universal Gates?
- The gates by which we can perform all the binary operations like Addition, subtraction, multiplication, and division.
- All the basic logic gates can be derived from them.
Properties of Universal Gates
- Universal gates are commutative but not associative in nature.
NAND Gate
NAND gate also called Negated AND, is one of the universal gates which is combination of NOT gate and AND gate connected serially. The combination of NAND gates can provide us AND, OR, and NOT gates.
The gate provides HIGH output signal(1) when both or either of input signal is LOW(0) and in other words output signal is LOW(0) when both the input signals are HIGH(1). The truth table of this gate is described below.
The NAND gate Boolean expression is given by:
Q= (A. B)’
Symbol Of NAND Gate
Truth Table Of NAND Gate
| A | B | Output(Q) |
| 0 | 0 | 1 |
| 0 | 1 | 1 |
| 1 | 0 | 1 |
| 1 | 1 | 0 |
Application of NAND Gate
- NAND gates can be used in alarm circuits.
- They re also used in buzzer and burglar devices
- NAND logic gates also have application in automatic temperature regulation circuits
- NAND gates can be used to detect if system has gone low. For e.g. Consider a security system build using NAND gates can monitor signals provided by sensors on doors and windows. If a single window or door is opened, the security system can output signal “1” and this can be used to trigger an alarm or take some other action.
Implementation of Other Gates Using NAND Gate
NOR Gate
NOR Gate also called negated OR, is another type of universal gates. It combines OR and NOT Gate
This gate gives a HIGH(1) output signal only when both of input signals are LOW(0) signals for rest it gives LOW(0) output signal
The NOR gate Boolean expression is given by:
A = (X + Y)’
Symbol Of NOR Gate
Truth Table Of NOR Gate
| X | Y | Output |
| 0 | 0 | 1 |
| 0 | 1 | 0 |
| 1 | 0 | 0 |
| 1 | 1 | 0 |
Applications of NOR Gate
- NOR Gate can be used in combinational circuits such as multipliers, multiplexers, half and full adders, and in ripple-carry adders.
- There are also used in sequential circuits and in shift registers. The sequential circuit is a circuit that has memory unlike combinational circuits and output can vary based on input. They have previous input, output, clock and a memory element.
Implementation of Other Gates Using NOR Gate
Conclusion
To conclude the gates whose combinations can form all other gates are called universal gates. The NAND gate gives LOW output signal only when all the input signals are HIGH where as NOR gate gives HIGH only when both input signals are LOW.
In this article we covered about properties and different types of universal gates.We discussed NAND and NOR gate in detail and its applications.
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