# Performance Factors of Basic Logic Gates

 9 Performance Factors of Logic Gates

A logic gate is an electronic circuit that outputs based on predetermined values. it has more than one input and one output signal. the output depends on the combinations of the input signals.

logic gates are an important part of the digital system that changes the previous history of the digital system. The hardware logic function is based on logical decisions.

There are only two values either "0" or  "1" in a logical algebra which is a unique property of the logic algebra system. Logic gates are based on different IC families. the most prominent family of logic systems are Transistor-Transistor Logic(TTL), metal oxide semiconductor(MOS), Complementary Metal oxide semiconductor(CMOS), and Emitter coupled Logic(ECL).

In this article, we discuss Different types of logic gates, their tables, diagrams etc. We also discuss the different performance factors of logic gates.

### Positive Logic

positive logic is defined as two states of logic one state is "high" which is called 5 volts and another state is "low" which is called 0 volts. This type of logic system is called positive logic.

In positive logic, 1 represents as
• An ON circuit
• A Closed Switch
• A High Voltage
• A Plus Sign
• A True Statement

### Negative Logic

Negative logic is defined as because of two states one state is "high" which is called 0 volts and another state is "low" which is called 5 volts. This type of logic system is called Negative logic.

In negative Logic, 0 represents as
• An OFF circuit
• An Open Switch
• A Low Voltage
• A Minus Sign
• A False Statement

But is not necessary that 1 represents a 5 voltage in a positive system and 0 represents a 0 voltage in a negative system. For example, for any circuit, if I say two-state of 5 volts and 9 volts which shows the low voltage of 5 volts and high voltage is 9 volts in the positive logic system and in the negative system the vice versa system is implemented.

## Types Of Logic Gates

Many types of logic gates are used in digital systems. but in this article, we discuss  3 basic logic gates and also discuss the performance factor of different logic gates defined below with the help of a table, symbol etc.

1. And Gate
2. OR Gate
3. Not Gate

## And Gate

The 2 inputs And gate have a total number of input combinations is 4. If we take 3 inputs of the logic gate the combinations of input are 8. there are two ways to define the gate one is by their symbol system and the other is equivalent to a switching circuit. both circuit symbol is shown below.

### Symbol of And gate

2 input AND gate table
 2 Inpur And Gate Table

### 3 Input AND Gate Table

 3 Inpur And Gate Table

### Operation of And Gate

The output is like a series circuit.
1. The AND gate has output "1" when Both inputs of the And gate are high in a two-input logic gate.
2. The AND gate has output "0" when Both inputs of the And gate are Low in a two-input logic gate.
3. If one input is high and the other input is low the output of the AND gate is also low.
4. If one input is "A" low and the other input "B" is high the output of the AND gate is also low.

### Boolean Expression

A.B = X  or  AB= X

## OR Gate

The 2 input OR gates have a total number of input combinations is 4 of each input. if we take 3 inputs of the logic gate the combinations of inputs are 8. Both the logic symbol and circuit symbol are shown below.

### Symbol of OR Gate

2 input OR gate table

### 2 Input OR Gate Table

3 input OR gate table

### Operation of OR Gate

The OR gate has output "1" when one of the inputs of or gate is high in a two-input logic gate. The OR gate has output "0" when Both inputs of the OR gate are Low in a two-input logic gate.

If one input is high and the other input is low the output of the OR gate is also High. If one input is "A" low and the other input "B" is high the output of the OR gate is also high.

Boolean Expression

A+B = Q

## Not Gate

Not gate is the complementary gate that inverts the input signal compared to the output signal. the other name for NOT gate is called an inverter.

### Truth Table of Not Gate

 Truth Table of Not Gate

### Operation of Not Gate

The working of not gate is simple when the input is high the output of the inverter is low and when the input is low the output of the gate is high.

Boolean Expression

A =B’

## Logic Gate Performance Factors

1. Supply Voltage
2. Input Voltage
3. Input And Output Currents
4. Output Voltage
5. Fan-in
6. Fan out
7. Propagation Delay Time
8. Noise Immunity
9. Power

### Supply Voltage

Most of the integrated circuits are designed at 5 volt supply voltage but some work also at other voltages range. for example, a CMOS works at a minimum of 1 volt. The regulation of supply voltage is limited to 0.25 for 5 volts.

### Input Voltage

The minimum voltage of the logic gate provides 1 input logic.

### Output Voltage

The minimum of high voltage provides the 1 output logic.

### Input & Output Currents

The input current level of any gate depends on the input voltage. the gate output current is also dependent on the output voltage.

### Fan-in

The number of inputs in a logic gate is defined as fan-in.

### Fan out

The ratio of Iol(max) and Iil(min) is called fanout.

### Propagation Delay Time

The switching speed of the logic gate is defined as propagation delay time. the time when a logic gate changes there condition from low output to high output. the time depends on the load and maybe a transistor in saturation condition.

### There are two types of noise margin

• low state noise margin
• high state noise margin

### Low State Noise Margin

Noise Immunity is defined as the difference between Vol(max) and Vil(max) and is called low state noise margin.

### High State Noise Margin

high noise Immunity is defined as the difference between VoH(max) and ViH(max) and is called High state noise margin.

The noise margin ensures that the gate is not triggered without their needs. the high noise margin defines the better work of the logic gate.

### Power

when switching in any circuit the power is dissipated across the resistance. The high switching means high power dissipation in the logic gate.

## Conclusion

Logic gates are the fundamental building blocks of digital electronics. They perform logical operations on binary inputs to produce a single binary output.

The basic types of logic gates include AND, OR, and NOT, which are the simplest forms of logic gates performing basic operations. Additionally, there are universal gates like NAND and NOR, which can be combined to perform any logical function.

Each gate has a unique truth table that outlines the output for every possible combination of inputs.

## Frequently Asked Questions – FAQs

### What are logic gates?

Logic gates are fundamental building blocks of digital circuits. They perform logical operations based on input signals and produce output signals according to predetermined truth tables.

### What are the basic types of logic gates?

The basic types include AND, OR, NOT, NAND, NOR, XOR, and XNOR gates.

### What is the function of an AND gate?

An AND gate produces a high output only when all of its inputs are high (1). It behaves like a logical "AND" operator.

### What is the difference between NAND and NOR gates?

NAND gates produce the opposite result of an AND gate, while NOR gates produce the opposite result of an OR gate. They are known as universal gates because they can be used to implement any other logic function.

### How are logic gates used in digital circuits?

Logic gates are combined in various configurations to perform complex logical functions, such as arithmetic operations, data processing, and control logic in digital systems like computers and microcontrollers.

### What is fan-out in logic gates?

Fan-out refers to the maximum number of inputs that a gate can drive.

### What is the propagation delay in logic gates?

Propagation delay is the time it takes for a logic gate to produce output after receiving input.

### Can logic gates have more than two inputs?

Yes, gates like AND and OR can have more than two inputs.