Basics of Digital Electronics

This tutorial is an introduction to Digital Electronics. You will learn about signals and their available types, what digital electronics is, its components, and how it uses digital signals. You will also learn about the advantages, limitations, and applications of digital electronics.

Contents:

  1. Signal and its Types
  2. Implementing Logic in Computers Using Digital Signals
  3. What is Digital Electronics?
  4. Components of Digital Electronic Circuits
  5. Integrated Circuits and Levels of Integration
  6. Advantages of Digital Circuits over Analog Circuits
  7. Limitations of Digital Electronics
  8. Real-Life Applications of Digital Electronics

Signal and its Types

A signal is a physical quantity that conveys some information, can be measured, and can be expressed in a mathematical form. There are mainly two types of signals:

  • Analog Signals: Analog signals are continuous signals, that is, they can have any values within a given range. For example, the human speech signal with its varying ranges of intensities and pitches. All signals occurring naturally are analog.
  • Digital signals: We can create another kind of signal which can only have limited values. Digital signals are discreet valued signals, which can have only certain values.

Analog signals are very difficult to process, as they offer a range of values and increase the complexity of a system. Therefore, the concept of digital signals came into existence with a fixed number of values attainable by a signal, reducing system complexity.

The following figure shows the two kinds of signals.

Analog and Digital Signals

In the figure, the analog signal can be seen as a continuous wave, whereas the digital signal has a stepped waveform with only certain attainable values, in this case, +5 Volts and -5 Volts.

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Implementing Logic in Computers using Digital Signals

The concept of ON and OFF state is used to develop logic in digital systems. To achieve this, computers used digital signal as follows:

  • The signal is given as input voltage pulses. A high voltage implies an ON condition and a low voltage implies an OFF condition (Positive logic). As the signal can have only two states, it is said to use binary logic. Numerically 1 and 0 are used to represent ON and OFF state respectively.
  • By permuting sequences of 0s and 1s, we can design systems that have fixed meanings for fixed-length sequences, and thus we can generate signals. If we increase the number of digits used per sequence, we can increase the number of signals with fixed meanings. For example, if we use a 2-digit sequence, we can have 00, 01, 10, 11 as the signals available and we can assign meanings to them, like 00 can stand for ADD.

To use digital signals, electronic hardware was required to implement ON-OFF logic and manipulate them to perform functions. Thus, Digital Electronics came up as a subject to fulfill these needs.

What is Digital Electronics?

Digital Electronics is a subject that deals with the design of systems that can take digital signals, perform operations and produce a digital output. These systems are usually circuitry that can be put on silicon chips, known as Integrated Circuits.

Digital Electronics also develops the concepts of number systems, Boolean algebra, and arithmetic’s used in various number systems. It mainly focuses on how to develop circuits, which can perform various operations like:

  • Arithmetic Operations for example Adding, Subtracting, Dividing, and Multiplying digits.
  • Logical Operations for example Comparing digits, Detect Changing Digits, Multiplexing, and Demultiplexing data.
  • Storing and Memorizing Operations for example storing digits, keeping count of iterations.

Digital Electronic circuits can further be studied in two major parts:

  • Combinational circuits: Combinational circuits develop implementations of functions like adding, subtracting, comparing, multiplexing, decoding, and all logic that do not require memorizing previous inputs.
  • Sequential circuits: Sequential circuits deals with the implementation of memory-based functions like storing data, counting, and latching.

All these functions together can then be used to build more complex systems.

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Components of Digital Electronic Circuits

The components of digital electronic circuits can be seen at three-level as follows:

  • At the higher level, digital electronic circuits, are made up of components like adders, subtractors, multiplexers, decoders, encoders, flip-flops, registers, counters etcetera.
  • At the middle level, all these higher components are made up of logic gates. We have logic gates like AND, OR, NOT called the fundamental gates, and many more derived gates.
  • At the lower level, the logic gates are made up of known analog electronic devices like transistors, resistors, diodes, or MOSFETS which are directly synthesizable on chips. The capability of these devices to act as a switch with varying high-low voltage pulses is utilized for generating ON-OFF logic.

We need fast switching behavior of components as we generate huge numbers of ON-OFF logic (1s and 0s) in digital circuits. Also, the analog components used here can be reduced to very tiny sizes as they need to perform limited action.

Integrated Circuits and Levels of Integration

Integration in general means uniting. For integrated circuits, it means uniting components on the chip. Due to the marvelous fabrication technologies, more components could be put on a single chip with reduced sizes.

Based on the number of components on a single chip we have the following levels of integration as shown in the figure:

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levels of Integration in Integrated circuits

As shown in the figure, there are broadly four levels of Integration in Integrated circuits:

  • Small Scale Integration (SSI): There are less than 100 components on the chip.
  • Medium Scale Integration (MSI): The number of components ranges from 100-1000 in medium-scale integration.
  • Large Scale Integration (LSI): The number of components ranges from 1000-10,000 components in Large Scale Integration.
  • Very Large Scale Integration (VLSI): There are more than 10 thousand components on the chip.

More number of components on a single chip means more computational power available for the same size. Thus, systems become faster, more efficient, and can carry out more operations in the same duration.

Advantages of Digital Circuits over Analog Circuits

Digital electronic circuits are advantageous over analog electronic circuits in many manners. Some of the key points where they differ are mentioned below.

  • Digital Circuits are easier to design compared to analog circuits as they involve switching operations in a HIGH- LOW comparative voltage manner and do not require an exact voltage to switch.
  • Digital circuits can be programmed extensively whereas analog cannot be programmed as much as digital circuits.
  • Digital circuits are less affected by physical conditions like temperature, pressure, humidity as compared to analog circuits. Also, analog circuits are more prone to noise.
  • Digital circuits are the most useful for the efficient storage of data. The memorizing logic implementation in digital electronics makes it possible. Analog circuits do not have this feature.
  • The same-sized chip can accommodate more amount of digital circuitry as compared to analog circuitry.

Limitations of Digital Electronics

Even after being advantageous, Digital Electronics get limited when it comes to interaction with the real world. Some of its limitations are:

  • It needs an analog to digital converter (ADC) for converting analog input to digital, as all signals occurring in nature are analog. Also, after producing digital output, it needs to convert the digital signal back to analog one using a digital to analog converter (DAC). Therefore, the processing time increases for Digital Systems.
  • For measuring very minor changes in a physical quantity, analog circuits are more useful than digital circuits as they are more sensitive to small changes and produce outputs high in precision.

Real-Life Applications of Digital Electronics

The applications of digital electronics can be seen all around us. Any gadgets which can display numbers have digital circuitry built into them. Few applications of digital electronics are:

  • Microprocessors and Microcontrollers.
  • Digital watches, digital thermometers, digital TVs
  • Mobile phones, Computers, Tablets
  • Traffic Lights
  • ATMs
  • Industrial automated equipment like CNC machines
  • Robotics

Key Points to Remember

The key points we need to remember about “Basics of Digital Electronics” are:

  • Signals are of two kinds: Analog and Digital. Analog is a continuous signal whereas digital
    signals are discreet.
  • Computers are given binary digital signals in the form of voltage pulses, varying as HIGH voltage and LOW voltage, represented by 1 and 0 respectively.
  • Digital Electronics is the study of systems that can process digital signals and give digital output.
  • All digital circuits are made up of logic gates, which can be made out of diodes, resistors, transistors, or MOSFETS.
  • Digital circuits are fabricated on small silicon chips, known as Integrated circuits (ICs).
  • Depending on the number of components on an IC, we have small-scale, medium-scale, large-scale, and very large-scale integrations.
  • Digital circuits are advantageous over analog circuits in terms of design, space consumption, memory storage, and robustness.
  • Digital electronics get limited due to time-consuming operations of analog to digital and back to analog conversion while using real-world signals as input.
  • The applications of digital electronics can be seen in microprocessors, home appliances, industrial equipment, gadgets, etc.

If you find any mistake above, kindly email to [email protected]

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Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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