Logic Gates: Definition, Types, Functions, and Symbols

Technological developments cannot be separated from electronic systems, especially digital electronics. Digital electronics are composed of logic gates. Then the logic gate will perform digital operations. Want to know about what are logic gates to logic gate symbols? This article will discuss about logic gates, Sinaumed’s, read this article to the end, OK?

Definition of Logic Gates

It is common that every science will always develop. Likewise with the science of electronics which is always experiencing development. Electronics itself can be interpreted as an electronic system that can be connected with a digital signal. Digital electronics originates from Boolean algebra and is used in many devices, such as telephones, computers, and so on.

Basically a digital signal has disjointed properties. In addition, this digital signal is usually denoted by an algebraic notation of 1 and 0. Notation 1 symbolizes the occurrence of a digital signal on an object. While the notation 0 symbolizes no relationship to an object.

Digital electronics is also known as another designation, namely digital circuits. Compiler of digital circuits are called logic gates. As the name implies, logic gates carry out logical operations. Usually logic gates perform logic operations on one or more inputs and produce a single output.

A logic gate is a digital electronics constructor in which every circuit in a logic gate works using the principles of Boolean algebra. Basically in electronics, an input and an output are built by what is called a voltage or current. This voltage is usually associated with a switch.

Therefore, logic gates can be thought of as various switches that implement Boolean algebra in electronic systems. With a switch, certain electronic items can be used properly. This is because a logical operation on one or more logical inputs will produce a solitary logic output .

The logic gate has several parts, namely resistors, transistors, and diodes. The three parts will perform simple operations or complex operations by simply combining several logic gates.

In the logic gate there is a section called an integrated circuit (IC). This IC has a function to limit the maximum number of logic gates. Prior to the development of integrated circuits (ICs), the number of logic gates required in digital electronics was minimal.

Each logic gate operation will be represented using a truth table. In the truth table, the number “1” indicates that the value is true (true) and the number “0” is worth false (false).

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Types of Logic Gates

The types of logic gates can be said to be the workings of the logic gates themselves. Logic gates have seven types of ways of working, namely AND logic gates, OR logic gates, NAND logic gates, NOR logic gates, X-OR (Exclusive OR) logic gates, and X-Nor logic gates (executive NOR) and NOT logic gates.

1. Logic AND Gate

AND logic gate is a logic gate that has two or more inputs and has one output. In the AND logic gate, the logic input is high if all of the logic outputs are also high. Vice versa, if the logic input is low, then the logic output will be low. You can find this logic gate in one of the electrical components, namely IC 7208.

A B Y
0 0 0
0 1 0
1 0 0
1 1 1

As previously said that every logic gate must have a truth table. The truth table shows that the logic gate can be activated or not. Therefore, based on the truth table above, it can be said that every output in the form of a number 0 means the AND logic gate cannot be activated.

From the truth table it can also be concluded that logic gates can only occur if the inputs are both “1”. If the input is the numbers “0” and “0”, the AND logic gate cannot be activated and if the input is the numbers “1” and “0”, the logic gate cannot be activated either.

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2. Logic OR gate

The OR logic gate is a very simple logic gate because it only uses resistors and transistors. The workings of the OR logic gate are two electrical power inputs. If one of the inputs is activated, the output will also be active. The OR logic gate can be found in the electrical components of the IC 7432.

A B Y
0 0 0
0 1 1
1 0 1
1 1 1

The logic OR truth table above explains that every two inputs that have the number “1” will produce the output number “1” as well. The number “1” indicates that the OR logic gate is correct and can be activated.

However, the OR gate becomes inactive when one of its inputs is the number “0”. In other words, the number “0” on the logic OR gate will produce an inactive or incorrect output.

3. NAND Logic Gates

The NAND logic gate is a combination of AND logic gates and NOT logic gates. From the two combinations of logic, it can be read as NOT AND or can be abbreviated as NAND. NAND logic gates can be found in the electronic components of the IC 7400.

A B Y
0 0 1
0 1 1
1 0 1
1 1 0

The truth table of the NAND logic gate explains that the input of the number “1” with the number “1” will produce an output of “0”. While entering the number “0” with the number “0” will produce the output number “1”.

From the truth table of the NAND logic gate above, it can be said that each output is the opposite of the output of the AND logic gate. Therefore, the NAND logic gate can be said to be the output of the logic gate of the AND logic gate which is inverted or negated.

4. Logic NOR Gate

The NOR logic gate is a combined logic gate of the OR logic gate and the NOT logic gate. You can find the NOR logic gate in an electrical component called IC 7436.

A B Y
0 0 1
0 1 0
1 0 0
1 1 0

Based on the truth table above, the NOR logic gate has two inputs and one output. Input in the form of the number “0” meets the number “0” will produce the number “1”. While the number “1” meets the number “1” will produce the output number “0”.

When viewed from the truth table, the output of the NOR logic gate is the opposite of the output from the OR logic gate. Therefore, the NOR logic gate can be said to be the output of an inverted OR logic gate.

5. XOR Logic Gate

The XOR gate is a combination of the NOT, AND, and OR gates. Apart from these three combinations, the XOR logic gate can also use a combination of other logic gates. Because it can be joined by many logic gates, the XOR logic gate is also called an exclusive gate. The XOR gate can be found in the electronic components of the IC 7486.

A B Y
0 0 0
0 1 1
1 0 1
1 1 0

The XOR logic gate has a truth table which produces two “1” outputs and two “0” outputs. If the input is the same number, it will produce “0”. Meanwhile, if the input is a different number, the output will be “1”.

Therefore, the XOR logic gate will issue a logic low if the two inputs have the same characteristics. Meanwhile, the XOR logic gate will output a logic high if the two inputs have different characteristics.

6. XNOR Logic Gate

The XNOR logic gate is a combination of the XOR logic gate and the NOT logic gate. From this combination of logic, it is abbreviated as XNOR or Exclusive NOR. XNOR logic gates can be found in the electronic components of IC 7266.

A B Y
0 0 1
0 1 0
1 0 0
1 1 1

The truth table of the XNOR logic gate explains that the same input will result in the number “1” output. Meanwhile, different inputs will produce an output in the form of the number “0”. So, it can be said that the XNOR truth table is the opposite of the XOR table.

The XNOR logic gate will produce a logic high output if the two characteristics are the same. Meanwhile, the logic output will be low if the input at the XNOR logic gate has different characteristics.

7. NOT Logic Gate

A logic NOT gate is a logic gate that can perform logic nullification or logic state inversion operations. Because of that, this logic gate is called the NOT logic gate. The NOT logic gate is also known as an inverter circuit. The NOT logic gate can be found in the electrical components of the IC 7404.

A Y
0 1
1 0

The truth table of the NOT logic gate illustrates that the input of the number “0” will produce the output of the number “1” and if the input is the number “1” it will produce the output number “1”.

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Based on the truth table above, it can be said that the NOT logic gate operates in reverse. Although the operation is reversed, the binary shape and level in the input signal operation can be maintained properly.

Logic Gate Functions

The main function of a logic gate is to form a digital path so that all components can be connected to each other properly, so that an electronic device works well too. In addition, logic gates can function as a system to command or translate a device.

In general, logic gates can be found in electronic devices in the form of chips . Inside the chip there are many components. Therefore, to connect each of the components on the chip , logic gates are present. In fact, inside the chip there are thousands of logic gates. Even though there are millions of logic gates, each gate has a different function.

However, in simple logic IC components only a few logic gates are found. For example on the TTL 7408 logic IC components.

In the TTL 7408 logic IC network above there are several networks, such as a flip flop network, a security network using a secret key, a counter network, a multiplexer network, a demultiplexer network, an encoder network, and a decoder network.

Logic Gate Symbol

Each logic gate has its own symbols. Below will be explained the symbols of each type of logic gate.

1. Logic AND Gate

In the symbol above, the AND logic gate has two inputs on the left. Meanwhile, there is only one output on the AND logic gate, namely the one on the right side. The AND logic gate will issue a logic high if the input characteristics are high, then the output will be high too.

2. Logic OR gate

In the symbol above, the OR logic gate has two inputs and one output. The OR logic gate will issue a logic high if there is an input with high characteristics, then the output of the OR logic gate will also be high. However, if all inputs have low characteristics, then the resulting logic will be low as well.

3. NAND Logic Gates

In the symbol above, the NAND logic gate has two inputs. Meanwhile, there is only one output on the NAND logic gate. The logic gate will output a logic high if one or all of the inputs have a logic low characteristic.

4. Logic NOR Gate

In the symbol above, the NOR logic gate has two inputs and produces one output. The logic NOR gate will be logic high if the inputs are both logic low. In other words, if there is a logic high input, the output will be a logic low.

5. NOT Logic Gate

In the symbol above, the NOT logic gate has an input of one. While the output of the NOT logic gate is only one. Each NOT logic gate will produce an output that is inversely proportional. For example, if the input is logic high, then the output will be low, and vice versa.

6. XOR Logic Gate

In the symbol above, the XOR logic gate has two inputs and only has one output. The XOR logic gate will issue a logic high if each input consists of a logic high and a logic low. In other words, any input that has the same logic will output a logic low.

7. XNOR Logic Gate

In the symbol above, the XNOR logic gate has two inputs with only one output. The XNOR logic gate will go high if the inputs have the same characteristic or logic amount. For example, two inputs with a low logic output a logic high and two inputs with a logic high output a logic high as well.

George Boole

Boolean algebra is a logical way to compare numbers to make a decision of right or wrong, or 1 or 0. This algebra was invented by a British mathematician named George Boole. He was born in 1815 and died in 1864. George Boole expressed his algebraic concepts in a book entitled An Investigation of the Laws of Thought, on Which Are Founded the Mathematical Theories of Logic and Probabilities in 1854.

George Boole made algebra in the book with the aim of showing how complex reasoning works in humans, so that it can be described through mathematical and logical forms.

Conclusion

Logic gates are the building blocks of digital electronic devices. Each logic gate can be represented by a truth table. Each truth table uses the algebraic system of Boolean. Therefore, the truth table consists of only the numbers “1” and the numbers “0”. Electronic components that use logic gates are usually chips .