# Digital Circuit : Basics, Circuit Design, Design Issues & Its Applications. (2024)

Digital circuits or digital electronics is a branch of electronics which deals with digital signals to perform the various task to meet various requirement. The input signal applied to these circuits is of digital form, which is represented in 0’s and 1’s binary language format. These circuits are designed by using logical gates like AND, OR, NOT, NANAD, NOR, XOR gates which perform logical operations. This representation helps the circuit to switch from one state to another for providing precise output. Digital circuit systems are mainly designed to overcome the disadvantage of analog systems which are slower and the output data which is obtained may contain an error.

## What is a Digital Circuit?

Definition: A digital circuit is designed by using a number of logic gates on a single integrated circuit – IC. The input to any digital circuit is in the binary form “0’s” and “1’s”. The output obtained on processing raw digital data is of a precise value. These circuits can be represented in 2 ways either in a combinational way or a sequential way.

### Digital Circuit Basics

Digital circuit design was first started up with a design of relays, later vacuum tubes, TTL Transistor-Transistor Logic, Emitter coupled logic, and CMOS logic. These designs use a large number of logical gates like AND, OR, NOT, etc integrated on a single IC. The input and output of digital data are represented in the logical truth table and timing diagram.

#### Logical Level

Digital data is represented in a logical format, that is in “0” and “1” format. Where logic 0 represents that the signal is low or “GND” and logic1 represents the signal is high or connected to “VCC” supply as shown below

#### Logical Truth Table

A logical truth table is a mathematical representation of the performance of digital signal when passed through the digital circuit. The table consists of 3 columns they are the clock column, input column, and the output column. For example, NOT gate logic table is represented as follows

 Clock Signal Input Logic Output Logic High 0 1 High 1

#### Timing Diagram

Digital signal behavior is represented in time domain format, for example, if we consider NOT logic gate truth table the timing diagram is represented as follows when the clock is high, the input is low then the output goes high. Similarly, when the input is high then the output goes low.

#### Gates

A logic gate is an electronic component that is implemented using a Boolean function. Gates are usually implemented using diodes, transistors, and relays. There are different types of logical gates they are, AND, OR, NOT, NANAD, NOR, XOR. Among which AND, OR, NOT are basic gates and NAND and NOR are the universal gate. Let us consider AND gate representation as below, which has 2 inputs and one output.

 Clock Signal Input Logic 1 Input Logic 2 Output Logic High 0 0 0 High 0 1 0 High 1 0 0 High 1 1 1

The truth table of AND gate

There are many ways in constructing a digital circuit that is either using logical gates by creating combinational logic, a sequential logic circuit, or by a programmable logic device that uses lookup tables, or by using a combination of many IC, etc. Typically, they are designed using combinational and sequential circuit format as shown below

### Combinational Logic Circuit

It is a combination of various logic gates like AND, OR, NOT. The design of combinational logic is made in such a way that the output depends on present input and the logic is independent of time. Combinational logic circuits are classified into 3 types, they are

• Arithmetic and logical functions: Adders, Subtractors, Comparators, PLD’s
• Data Transmissions: Multiplexers, Demultiplexers, Encoders, Decoders
• Code Converters: Binary, BCD, 7-segment.

### Sequential Circuit

The design of the sequential circuit is different from the combinational circuit. In a sequential circuit, the output logic depends on both present and past input values. It also consists of a memory element which stores the processing and processed data. Sequential circuits are classified into 2 types they are,

• Synchronous Circuit
• Asynchronous Circuit

Some of the examples of sequential circuits are flip flops, clocks, counters, etc.

### Digital Circuit Design

Digital circuits can be designed in the following ways they are

• Using sequential system representation and combinational system representation
• Using the mathematical methods by reducing logical redundancy algorithms like K-Map, Boolean Algebra, QM algorithm, binary decision diagrams, etc.
• Using data flow machines which consist of registers and buses or wire. Data is communicated among various components using buses and registers. These machines are designed using hardware description languages like VHDL or Verilog.
• A computer is a general-purpose register transfer logic machine designed by using a microprogram and microsequencer processor.

### Digital Circuit Design Issues

Since the digital circuits are build up with analog components like resistors, relays, transistors, diodes, flip flops, etc. It is necessary to note that these components do not affect the behavior of the signal or data during digital circuit operation. The following are design issues which are usually observed they are,

• Problems such as glitches may occur due to inappropriate design of the system
• In-proper synchronization of a different clock signal leads to metastability in the circuit
• Digital circuits calculate more repeatedly due to high noise immunity.

#### Digital Circuit Examples

The following are the examples of digital circuits

• Mobile phones
• Calculators, etc.

• Accuracy and programmability is high
• Easy to save digital data
• Immune to noise
• Many digital circuits can be integrated on a single IC
• Highly flexible
• High reliability
• A high rate of transmission
• Highly secure.

• They operate only on digital signals
• Consumes more energy than analog circuits
• Heat dissipation is more
• High cost.

### Applications

The following are the applications

• ADC – Analog to digital converter
• DAC – Digital to analog converter
• Signal Generator
• CRO
• A smart card, etc.

### FAQs

1). What are digital circuits used for?

Digital circuits are used to perform Boolean logic operations.

2). How does digital circuit work?

Digital circuit works with discrete signals, which are represented in the binary form of 0’s and 1’s.

3). What are the basic components of the digital circuit?

The basic components of the digital circuits are flip flops, diodes, transistors, Gates, etc.

4). What is a circuit made of?

An electronic circuit is made up of a number of passive and active components, which are connected using conducting wires.

5). Name a few examples of Active and Passive components?

• Examples of active components are diodes, IC, triode vacuum tubes, etc.
• Examples of passive components are resistor, capacitor, inductor, transformer, etc.

6). Why do we use a resistor in circuits?

We use a resistor in the circuit in order to control the current flow.

An electronic circuit is made up of a number of passive and active components, which are connected using conducting wires. They are two types of circuits they are analog circuit and digital circuit. The input to an analog circuit is a continuous variable signal, which provides signal information like current, voltage, etc. The digital circuit input signal is in a discrete time-domain format, which is represented in “0’s” and “1’s”. It provides signals strength, noise ratio, attenuation, etc properties of a digital signal. The main advantage of using digital circuits is that they are easy to implement and understand.

## FAQs

### What are the design issues in digital circuits? ›

These aspects can affect the functionality, reliability, and performance of the circuit, as they introduce parasitic elements, such as resistance, capacitance, and inductance, that can alter the signal characteristics. They can also cause problems such as crosstalk, noise, interference, and heat dissipation.

What is the basic digital circuit design? ›

Digital Circuits are designed using logic gates, diodes, transistors, inductors, capacitors, and resistors. As Digital Circuits follow Boolean Laws, the logic expressions should be simplified for a small circuit. Small the digital circuit, the easier for it to be embedded in Integrated Circuits (ICs).

What are digital circuits and its applications? ›

Applications of Digital Circuits

The display of digital watches is designed based on digital circuits. Rocket science and quantum computing use digital electronics. The automatic doors work on the principle of digital electronics. Everyday encounters with traffic lights are based on digital circuits.

What is digital logic design and its application? ›

Digital logic design is a system in electrical and computer engineering that uses simple number values to produce input and output operations. As a digital design engineer, you may assist in developing cell phones, computers, and related personal electronic devices.

What are four basic types of circuit problems? ›

There are a total of four possible failures that can take place in an electrical circuit: an open circuit, high resistance, short-to-ground and short-to-power.

What is an example of a digital circuit design? ›

Common Examples of Digital circuits are timers, counters and state machines. Digital circuits usually form part of the overall complex circuit board design in terms of logic gates & finite state machines (FSM). Sometimes, using few gates & FSM chips would be economical and simpler than complex microcontroller systems.

What are the most basic components of a digital circuit? ›

Logic gates are the fundamental building blocks of digital circuits. They are electronic components that perform basic logical operations such as AND, OR, and NOT. The most common types of logic gates include AND, OR, NOT, NAND, NOR, and XOR gates.

What are the different types of digital circuits? ›

Types of Digital Logic Circuits:
• Synchronous Systems:
• Asynchronous Systems:
• Combinational Logic Circuits:
• Sequential Networks:
Oct 9, 2021

What are the 3 components needed in a basic circuit design? ›

Electric circuits

An electric circuit has three parts: An energy source – like a battery or mains power. An energy receiver – like a lightbulb. An energy pathway – like a wire.

What devices use digital circuits? ›

Examples of such devices are computers, information appliances, digital cameras, digital televisions, flash memory, key USB memory, mobile phones, hard disks, and devices of computer memory.

### What devices have digital circuit? ›

Many of our household items make use of digital electronics. This could include laptops, televisions, remote controls and other entertainment systems, to kitchen appliances like dishwashers and washing machines. Computers are one of the most complex examples and will make use of numerous, complex circuits.

What is the difference between electrical and digital circuits? ›

In electronic design, an analogue circuit is one that uses voltage or current levels that vary continuously with time to represent signal amplitude. This is in contrast to digital circuits, which use a discrete set of signal levels, usually two voltages or currents, that represent signal amplitude.

How does a digital circuit work? ›

A digital circuit is typically constructed from small electronic circuits called logic gates that can be used to create combinational logic. Each logic gate is designed to perform a function of Boolean logic when acting on logic signals.

What are the applications of analog and digital circuits? ›

Analog electronics can be used to amplify signals, filter noise, and perform a wide variety of other functions. Some common components used in analog electronics include resistors, capacitors, inductors, and transistors. Digital electronics, on the other hand, use discrete signals to represent and process information.

Digital design refers to a type of visual communication that presents information to users on an electronic device, such as a computer, tablet, or mobile phone.

What are the 3 main issues in designing distributed systems? ›

Problems
• Unreliable Network : When a system is divided into two separate parts, communication between parts can sometimes become unreliable or unavailable.
• Inconsistent Data: In a distributed system there can be inconsistencies when nodes have different versions of the same data. ...
• Node Failures: Nodes can fail.
Feb 1, 2023

What is the design issue? ›

A design issue often represents a challenging problem through the operational requirements and capabilities of a robotic system. A design issue is usually a very important item of the design process that will lead to specific design solutions.

What are the disadvantages of digital circuits? ›

In comparison to the analogue system, the digital system uses more energy. Calculations and signal processing use up this energy, which causes heat to be generated. These systems cost a lot of money. The electronic systems are brittle.

What is system design issues? ›

- Performance, reliability, availability, consistency, scalability, security, versatility, modularity/simplicity. • Designers face trade-offs: - Availability vs. consistency.

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