Basic Logic Gates;Complete Guide You Must Know

Basic Logic Gates are a type of elementary digital circuit that works based on Boolean logic. A digital circuit is one that processes information as a binary digit (either 0 or 1) in order to do something useful with it. Boolean logic is the set of rules used to manipulate these bits and create more complex logical representations of the information. Intuitively, logic gates can be thought of as virtual on/off switches.

They take input signals and output an “on” or “off” signal depending on whether the input meets certain conditions. These conditions are often based on things like whether the input signal is greater than some threshold, or whether two combined inputs have a particular logical relationship to each other. These operations are known as logical operators , and we will explore each of them in detail below .

Basic Logic Gates;Complete Guide You Must Know

Index of contents

  • What is digital electronics?
  • What are logic gates made of?
    • logic families
      • TTL
      • CMOS
      • ECL
      • DTL
      • other families
    • Advantages of digital electronics
    • Disadvantages of digital electronics
  • The importance of logic gates
  • digital signs
  • What is a logic gate?
  • Boolean logic and its implications
  • How do logic gates work?
  • Logic gate symbols and how to read them
  • types of logic gates
    • Buffer or direct logic gate
    • Inverter or NOT
    • AND
    • OR
    • NAND
    • NOR
    • Exclusive OR (XOR)
    • XNOR
  • Quantum logic gates
    • Main differences between quantum and digital logic
    • Differences in the laws of physics

What is digital electronics?

Digital electronics is electronics that uses discrete voltages (as opposed to analog electronics, which uses direct voltages). The most common type of digital electronics is binary digital electronics, which uses discrete voltages that are either high (above a certain threshold) or low (below a certain threshold) or binary digits (0 or 1). Digital electronics has many applications, such as computers, mobile phones and other digital devices.

What are logic gates made of?

logic gate is not an electronic element or component, but rather they are made of elementary electronic components (resistors, transistors, capacitors,…). Depending on the logic family (TTL, RTL, CMOS,…) they can be made up of one component or another. For example, TTL uses bipolar transistors, RTL uses a combination of resistors and transistors, while CMOS uses MOS-type unipolar transistors to compose each of the logic gates.

logic families

There are a wide variety of logic families to choose from when building an electronic circuit. Each logic family has different properties, which makes them useful for specific applications. Understanding the pros and cons of each logic family is essential to getting the best design for your circuit.



The terms logic family, logic level, and logic voltage refer to the same concept: how digital something is. There are many logic families, but in general they can be divided into CMOS, TTL, ECL, etc. Although there may be other ways to categorize these circuits, this article will focus on these five popular types.


TTL stands for Transistor Logic . It refers to any digital logic circuit that uses transistors (electronic devices that can be used as switches) controlled by voltages between 0 V and 5 V. The transistor was invented in the 1950s and was intended to replace vacuum tubes. Since then it has become a ubiquitous and important electronic device, present in analog and digital electronic circuits.

The main advantage of TTL is that it can be made with transistors that operate at very low voltages . This is important because transistors are cheap and easy to manufacture. TTL has a high voltage requirement: both the power supply and the signals must be between 0 V and 5 V. This makes TTL circuits expensive to build in large-scale applications because they require special power supplies. The TTL family is also difficult to design because the voltages are very specific.


CMOS stands for complementary metal-oxide-semiconductor. It is a family of digital circuits that use transistors and capacitors to create a voltage between 0 V and V (where V is approximately 5 V). Like TTL, CMOS circuits are widely used in digital devices because they are cheap and easy to manufacture.

The CMOS is also a low-power circuit , which means that it can use less electricity than other types of circuits. It’s also low noise, which means it doesn’t produce a lot of static or other types of interference. The CMOS has a high input resistance, which means that it is easy to connect to other devices such as sensors. It is also very immune to noise, as its low input resistance makes it difficult for noise to enter the circuit.


ECL stands for Emitter Coupled Logic . This family uses voltage levels between 15 V and 35 V. ECL is typically used in high-end applications such as high-speed computers and high-frequency RF communications. ECL is a difficult logic family to design because the signals are very high voltage.

It’s also quite a complicated circuit: emitter-coupled logic is done with a combination of transistors, diodes, and resistors. The ECL is a low power circuit, but it requires special power supplies to operate. It also has a high input resistance, making it suitable for high-speed applications.


These two logic families are similar to CMOS in that they are low voltage, high current circuits. DTL stands for diode-transistor logic.

Since DTL and DTLC circuits require low voltages , they can be powered by alkaline batteries. They also have high input resistance and are immune to noise. DTL and DTLC circuits are also low voltage so they can be made with cheap transistors. However, they have low input current, which means they consume less power than other circuits.

other families

Other logic families exist , but are less common. Acronyms include PECL, HCTL, RTL, PCTL, and ECL. PECL stands for Positive ECL, HCTL stands for High Current ECL, RTL stands for Resistor-Transistor Logic, PCTL stands for Positive Coupled Transistor Logic, and ECL stands for Emitter Coupled Logic.

These other logic families are similar to those mentioned above. However, they have different voltage levels, power requirements, input resistances, and other properties. It is important to understand what each of these logic families is capable of and how to design circuits with them.

Advantages of digital electronics

  • Scalable– Digital systems can be expanded simply by adding more components. This is useful when there is an unexpected increase in demand on a system.
  • Fault Tolerance– Digital circuits are often fault tolerant. This means that if one part of the circuit fails, the rest of the system will continue to function as expected.
  • Precision– Digital circuits can be programmed to perform specific tasks. This makes them more useful than analog circuits for precision tasks like robot control.
  • Versatile– Digital circuits can perform different functions depending on how they are programmed.
  • Low Power Consumption– Compared to analog circuits, digital circuits consume less power.

Disadvantages of digital electronics

  • Expensive– Digital circuits are usually more expensive than analog.
  • More difficult to understand:Digital circuits are more complex than analog circuits. This makes them more difficult to understand, which can lead to incorrect implementations.

The importance of logic gates

Logic gates are the building blocks of all modern computers : the computers that run our world, store information, and process data. The rise of computers in the last century has had a profound impact on our society and our daily lives, and it is hard to imagine what our world would be like today without computers.

Although computers have had a huge impact on our world, logic gates are the essential components of all computers, from the first vacuum tube-based computers in the 1950s to today’s modern silicon-based computers. Silicon -based computers are present in almost all of our modern computing devices, from computers, tablets, and smartphones to cars, medical devices, and even home appliances.

digital signs

A digital signal is a signal that is either on (a 1) or off (a 0) . Digital signals do not have the same amplitude as an analog signal (that is, they have a finite value, which can be 0 or 1). Because they have a finite value, they are a convenient way to represent information, such as letters and numbers. An example would be a computer displaying an image of a flower. If a human could see the data coming out of the computer, he would see a series of 0s and 1s. The 0’s would represent the black pixels and the 1’s the white pixels.

What is a logic gate?

Logic gates are at the core of all digital circuits. They receive a set of input signals and output an “on” or “off” signal based on some rule that you can specify . For example, an “AND” gate receives two inputs, and if both are “on”, the output is “on”. If one or both inputs are “off”, the output is “off”. This sounds simple enough, but it becomes more interesting when you consider that these gates can be combined to create what are called circuits.

digital circuit is a set of logic gates connected together in such a way that the output of one gate becomes the input of another. For example, the following circuit uses two AND gates, an OR gate, and an inverter to perform a very simple function: When the switch is on and both sensors detect motion, the LED turns on. When the switch is off or any of the sensors detect movement, the LED turns off.

Boolean logic and its implications

Before we get into how to troubleshoot logic gates, we first need to know what Boolean Logic actually is. The most important concept in the fundamentals of digital circuits is Boolean Logic.

Boolean logic is the language used to describe how to manipulate bits (a single digit 1 or 0) and create more complex logical representations of information. In Boolean logic, the state of a digital circuit can be described using two values: true and false. A single bit can only have one of two values: 1 or 0, true or false. Boolean logic can also be used to represent the state of an entire system, such as the state of an entire computer program. Boolean logic is a useful tool because it allows us to represent very complicated systems with just a few simple values, which can be easily manipulated and interacted with.

How do basic logic gates work?

To understand how logic gates work , let’s start with an example. Let’s say we want to make a circuit that outputs a “0” (low voltage) if a certain input/switch is pressed, or a “1” (high voltage) if that input is not pressed. To do this, we will use a “NOT” logic gate. A NOT gate has one input and one output. When the input is “on”, the output is “off” and vice versa.

We can decide what to use as input by thinking about what we want the circuit to do .when the input is pressed. If the input is pulsed, we want the circuit to output a low voltage. If the input is not pressed, we want the circuit to output a high voltage. So to put this into practice, we have an input connected to a button. When the button is pressed, the input is “on”, and if the button is not pressed, the input is “off”. So we have a NOT gate connected to the input, with the output of the NOT gate connected to a voltage source. When the input is “on”, the output of the NOT gate is “off” and vice versa. Thus, when the button is pressed, the voltage source is connected to ground through the button, and when the button is not pressed, the voltage source is connected to a high voltage through the NOT gate.

Logic gate symbols and how to read them

Logic gate symbols are a pictorial representation of how a specific logic gate works. Let’s take a look at a NOT gate and see how to read its symbol. This symbol consists of three parts:

  • Tickets:always displayed on the left side of the symbol.
  • Exit: the door exit is always displayed on the right side of the symbol.
  • Door (Bridge)– Shown in the center of the symbol.

Obviously, there are several nomenclatures , so the symbols vary from one to another depending on which one is used.

Types of basic logic gates

There are several different types of logic gates, each of which takes two inputs and produces one result.

Buffer or direct logic gate

It is the opposite of the NOT or inverting gate, that is, a direct or buffer gate . If its input is 0 the output will be 0, and if the input is 1 the output will be 1. These types of gates are used a lot, like in some patch pads, etc.

Inverter or NOT

An inverter is a basic logic gate with a single input and one output. An inverter takes a high voltage input and gives a low voltage output, and takes a low voltage input and gives a high voltage output. In other words, always invest. If the input is 1 the output is 0 and if the input is 0 the output is 1.


An AND gate is a logic gate that produces a high voltage when all of its inputs are high voltage. The output of an AND gate is high voltage when all inputs are high voltage or when a low voltage input is applied through a NOT gate.


An OR gate outputs a high voltage when any of its inputs is high voltage. A high voltage input through a NOT gate becomes a low voltage output, so the output of an OR gate is high when any of its inputs is high.


NAND gate produces a low voltage when all of its inputs are high voltage. A high-voltage input through a NOT gate becomes a low-voltage output, so the output of a NAND gate is low-voltage when all inputs are high-voltage or when one low-voltage input is applied. through a NOT gate. That is, it is the result of the combination of an AND + NOT gate.


NOR gate outputs a high voltage when all of its inputs are low voltage. A low-voltage input through a NOT gate becomes a high-voltage output, so the output of a NOR gate is high-voltage when all inputs are low-voltage or when one low-voltage input is applied. through a NOT gate. That is, it is the combination of an OR + NOT gate.

Both the NAND gate and the NOR gate are considered to be universal gates. And that is so because any other door can be represented with them. For example, to create an inverter, it would suffice to bridge its inputs. Thus, any circuit with multiple different logic gates can be implemented with only NOR gates or only NAND gates.

Exclusive OR (XOR)

An exclusive OR gate outputs a high voltage when either input is high, but a low voltage when both inputs are low. A high-voltage input through a NOT gate becomes a low-voltage output, so the output of an exclusive-OR gate is high-voltage when any of its inputs is high-voltage or when a low-voltage input is applied. low voltage through a NOT gate.


XNOR is short for “exclusive-NOR” , and refers to a type of logic gate that outputs a 1 only when the two inputs are different. In other words, XNOR would be the inverse of XOR. XNOR logic gates are commonly used in computer design to check if two pieces of data are the same or different from each other. They are also used in digital signal processing to invert them. That is, XNOR logic gates are especially useful when you need to ensure that two inputs are different.

Quantum logic gates

Quantum computers are based on quantum logic gates that can manipulate individual quantum bits (qubits) instead of binary bits. Quantum logic gates differ from traditional logic gates in that they employ superposition and entanglement instead of on and off states.

Main differences between quantum and digital logic

Quantum computing differs from digital computing in three ways:

  • Data is processed in bits versus qubits.
  • Data is processed sequentially versus parallel.
  • The state of the system is measured in relative versus absolute.

Therefore, the logic gates and digital logic of quantum computing do not fit the quantum computing paradigm.

Differences in the laws of physics

The most important difference between quantum logic and digital logic is that quantum computers are based on different physical laws . Quantum computers use the rules of quantum physics, while digital computers use the rules of classical physics. These differences go beyond the way computers store information. They affect everything else, including how computers are designed and programmed.


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