Digital Electronics

Basic Elements of Digital Electronics

Elements of Digital Electronics: logic gate, Adders, Subtractor, Comparator, Flip–Flop, Timers & Clocks, Multiplexer and Demultiplexer

Elements of Digital Electronics:

The various basic elements playing a crucial role in digital electronics are as follows (a brief introduction of these elements is being presented here, its detail will be presented in the coming articles)

Logic Gates in Digital Electronics

The decision-making capability of gate circuits in digital electronics is called logic. And a logic circuit, which performs a certain logic operation (e.g. AND or OR), is known as gate. As such logic gates are electronic circuits, which conduct logic decisions and their output depends on preset conditions. The input of a logic gate is greater than 1 but its output is just 1. A logic gate operates just like a switch that can either be turned ON or turned OFF. The ON state normally denotes logic 1 whereas the OFF condition represents logic 0. Apart from adding, subtracting, counting, etc., a gate can also store information. Some common examples of gates are AND, OR, NAND, NOR, Invertor or NOT, XOR and XNOR. Thus, a logic gate is the basic building block, on which a digital system comes into existence. It has to be remembered that gates are also known as logic circuits, digital circuits, or switching circuits. Now –a – days, logic gates are available in the shape of various IC families (e.g. transistor, transistor logic or TTL, emitter-coupled logic ECL, metal oxide semiconductor or MOS, and complementary metal oxide semiconductor (CMOS).

Adders in Digital Electronics

The logic circuits, which are used to add two binary numbers, are called adders. In other words, a circuit used in digital computers, which performs the operation of addition, is known as an adder. There are two types of an adder. One type is known as half – adder and the other one is called full – adder. A digital device or circuit, which performs the task of two bits, is called half – adder.  And the logic circuit, which can add three bits simultaneously, is called a full adder. A half–adder can be formed by means of AND gate consisting of two inputs and an XOR gate consisting of two inputs, whereas for making a full adder, two half-adders and one OR gate are used.

Subtractor in Digital Electronics

A logic circuit, which is used to subtract two binary numbers, is called a subtractor. In other words, the circuit which is used for subtracting binary numbers is known as a subtractor. Like an adder, a subtractor has two types as well. Half subtractor and full subtractor. However, some of the adders are such that apart from conducting plus or addition operations, also tend to perform minus or subtraction operations. Such adders are called universal adders. These are also known as adder–subtractors.

Comparator in Digital Electronics

A device that explains or expresses the relationship between two binary quantities after a mutual comparison between the two, is called a comparator. In simple words, a comparator makes the comparison between two binary quantities and exposes whether these two quantities are mutually equal or not. For this purpose, an exclusive OR gate or XOR gate is used.

Flip–Flop in Digital Electronics

A simple electronic circuit that is used as a memory element, is known as a flip–flop. In other words, a digital logic circuit, which can store just one bit of a binary number, is called a flip–flop. A flip-flop is a simple type of a sequential circuit (a digital circuit, the logic conditions of which depend on a specific time sequence, is called a sequential circuit). The main objective of this type of circuit is memory or storage. It is used in timing operations and arranging different types of data counting storage into a proper sequence. In fact, it is a bistable multi-director, which is capable of storing or memorizing just one bit of information.

Timers & Clocks in Digital Electronics

These are such electronic circuits that generate digital signals in a specific sequence and on the basis of these very signals, flip–flops and circuits carry out their usual operation.

Shift Registers in Digital Electronics

A register is a group of flip – flops, which can store information temporarily. In other words, a memory device that is used for a temporary type of storage is called a register. A register that transfers or shifts one bit of data during a piece of time from one element to another end-to-end element on the left or right side, or shifts data with every clock pulse, is called a shift register. It is worth remembering that all shift registers are operated via an input clock or shift pulse. The shift register can also be defined as follows:

A group of flip–flops, which are interconnected in such a manner, that a binary number may be shifted out or transferred into the group, is called a shift register.

Counters in Digital Electronics

As the name suggests, the counter is a circuit that primarily performs the function of counting. Counters are digital circuits, which are assembled by means of inter-connecting a series of flip–flops. Counters are used for the counting of these electronic events or pulses, according to which flip–flops continue to change their condition. Counters are the heart of nearly all digital systems and computers, which apart from counting are also useful for producing timing signals in order to control the operation of digital systems. A counter can count up to a maximum of 2n. Here “n” means the number of flips – flops e.g. 23 = 8 & 24 = 16. As counters have the capacity to store a binary number, therefore they are analogous to a store register. Remember that input of a counter is a constant type of waveform or a clock pulse and every time when a clock signal changes its state or condition (that’s getting from low to high), the counter adds 1 in its sum of numbers.

Memories in Digital Electronics

These are digital circuits, which help in storing computer programs and data, either for a long or short period of time. Remember that as compared to a flip–flop, memories have the capacity to store thousands of words within it. The function of memory in a digital computer may be compared to the mind working in a human body. The objective of memory is to store necessary instructions or information about some sort of glitch, apart from storing data about a certain problem.

Multiplexer or Data Selector

A digital device, which selects just one input out of a number of inputs and transmits it on the output, is called a multiplexer or data selector. In other words, a circuit, which selects just one line or channel from amongst numerous input lines within a specific time sequence, is known as a multiplexer. Multiplexer resembles a rotary mechanical switch and it is frequently used for the conversion of parallel inputs to serial outputs. In simple words, a data selector can also be defined as a circuit, which selects data from numerous inputs within an explicit time sequence and then provides it on output. It is shortly known as MUX.

Demultiplexer or Distributor

It is a device, which performs the task of distribution of data. it is exactly the opposite of a multiplexer. In other words, a demultiplexer is an electronic circuit, which consists of an input and numerous outputs. It is normally used for the conversion of serial data to parallel mode.

Encoder in Digital Electronics

An electronic device, which converts decimal numbers (or non-binary numbers) to binary numbers, is called an encoder. In other words, a device that converts information to coded form is called an encoder.

Decoder in Digital Electronics

The decoder is a kind of logic circuit, which converts binary numbers (or coded information) into decimal numbers. It is worth mentioning that the decoder is absolutely reversed to an encoder (for an explanation, see figure 1.5). Furthermore, a decoder can also sense or feel about the presence of a particular number or a word.

Digital Electronics decoder
Figure 1.5

Coded Inverter

A logic circuit, which converts one type of binary code to other types of binary code, is known as a code converter. Decoders and encoders can also be termed as special forms of code converters. Code converters are mostly used in digital systems, wherein two or more two binary codes are being used.

Basic Terms Related to Digital Electronics

Some important terms related to digital electronics, knowledge about which is necessary, are as under:


The word “bit” is an abbreviation of a binary digit. Any binary digit or figure between 0 to 9 in the binary system is known as a bit. It is the smallest unit of binary data. Two separate voltage levels are used in digital circuits for indicating two bits (0 & 1).

As different digits or words are a combination of a number of bits, therefore bits are indicated in various groups e.g. kilo bit, megabit etc.


A collection of 8 – bits is known as a byte.


A collection of four digits or four bits is known as a nibble. In other words, a nibble is equivalent to a half byte.


The collection of a few bits (4, 8, or more than that), is known as a word. In other words, a complete unit of information or binary data is called a word. And it normally consists of one or more bytes.


Groups of bits are called codes, which are used to indicate numbers, letters, symbols and instructions, etc.


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