PDF | On Jan 1, , D.K. Kaushik and others published Digital Electronics. Logic Operations: Three basic logic operations (AND, OR and NOT) are used. The Basics of Digital Electronics. Until now I have mainly covered the analog realm of electronics—circuits that accept and respond to voltages that vary. Sample Chapter of Digital Electronics (Vol-6, GATE Study Package). INTRODUCTION. This chapter, concerned with the basic study of Boolean algebra and.
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in the available books on the subject of digital Digital Electronics: Principles, Devices and App Foundation of Digital Electronics and Logic Design. Basic Digital Concepts. By converting continuous analog signals into a finite number of discrete states, a process called digitization, then to the extent that the . BASICS OF DIGITAL ELECTRONICS. Digital electronics represent signals by discrete bands of analog levels, rather than by a continuous range (Source.
Digital Logic designers build complex electronic components that use both electrical and computational characteristics.
Bi-stable devices popularly called Flip-flops described in Modules 5. Teaching notes Page 10 K2 Complete the definitions of electronic and electrical technology. Digital Logic Design is foundational to the fields of electrical engineering and computer engineering. Today I am going to share with you all the notes related to Analog Electronics subject for gate. Electronics and Communication Engineering students. The modules refer to a 6 V supply, but they work well at 5 Volts. These notes are of Made Easy coaching institute, New Delhi.
Bi-Stable Logic Devices. Frequently additional gates are added for control of the. There are two oscillators in TRC Digital circuits form the backbone of modern day gadgets like cell phone, digital cameras, GPS displays, etc. An analog device, then, is one that has a signal, which varies continuously in time with the input, whereas, a digital device operates with a digital signal that varies discontinuously.
To understand the operation of each digital module, it is necessary to have a basic knowledge of digital circuits and their logical function. This is the scan copy of the note books written by students studying in some very reputed coaching institute taught by very well known name in education field. Digital Electronics Notes EC pdf free download. Notes digital electronics module Flip flop are also used to exercise control over the functionality of a digital circuit i.
Figure 1. By converting continuous analog signals into a finite number of discrete states, a process called digitization, then to the extent that the states are sufficiently well separated so that noise does create errors, the resulting digital signals allow the following slightly idealized Digital Electronics Lecture Notes for 3rd Semester B. Its objectives are to: Introduce registers as multi-bit storage devices. Consequently the output is solely a function of the current inputs.
Lecture Notes for Digital Electronics. Digital Electronics Lecture Notes. By converting continuous analog signals into a finite number of discrete states, a process called digitization, then to the extent that the states are sufficiently well separated so that noise does create errors, the resulting digital signals allow the following slightly idealized ECE — Digital Electronics Multiplexers, Decoders and Encoders Lecture 16 The slides included herein were taken from the materials accompanying Fundamentals of Logic Design, 6 th Edition, by Roth and Kinney, and were used with permission from Cengage Learning.
As per Anna university syllabus of regulation as well we provided important 2 marks and 16 marks questions with answer for all units. Notes Credits to Prof. The bipolar junction transistor was invented in From onwards, transistors replaced vacuum tubes in computer designs, giving rise to the "second generation" of computers. Compared to vacuum tubes, transistors have many advantages: Silicon junction transistors were much more reliable than vacuum tubes and had longer, indefinite, service life.
Transistorized computers could contain tens of thousands of binary logic circuits in a relatively compact space. At the University of Manchester , a team under the leadership of Tom Kilburn designed and built a machine using the newly developed transistors instead of vacuum tubes.
While working at Texas Instruments in July , Jack Kilby recorded his initial ideas concerning the integrated circuit then successfully demonstrated the first working integrated on 12 September In the early days of integrated circuits, each chip was limited to only a few transistors, and the low degree of integration meant the design process was relatively simple.
Manufacturing yields were also quite low by today's standards. As the technology progressed, millions, then billions  of transistors could be placed on one chip, and good designs required thorough planning, giving rise to new design methods.
An advantage of digital circuits when compared to analog circuits is that signals represented digitally can be transmitted without degradation caused by noise. In a digital system, a more precise representation of a signal can be obtained by using more binary digits to represent it. While this requires more digital circuits to process the signals, each digit is handled by the same kind of hardware, resulting in an easily scalable system. In an analog system, additional resolution requires fundamental improvements in the linearity and noise characteristics of each step of the signal chain.
With computer-controlled digital systems, new functions to be added through software revision and no hardware changes. Often this can be done outside of the factory by updating the product's software. So, the product's design errors can be corrected after the product is in a customer's hands. Information storage can be easier in digital systems than in analog ones. The noise immunity of digital systems permits data to be stored and retrieved without degradation.
In an analog system, noise from aging and wear degrade the information stored. In a digital system, as long as the total noise is below a certain level, the information can be recovered perfectly. Even when more significant noise is present, the use of redundancy permits the recovery of the original data provided too many errors do not occur.
In some cases, digital circuits use more energy than analog circuits to accomplish the same tasks, thus producing more heat which increases the complexity of the circuits such as the inclusion of heat sinks. In portable or battery-powered systems this can limit use of digital systems.
For example, battery-powered cellular telephones often use a low-power analog front-end to amplify and tune in the radio signals from the base station. However, a base station has grid power and can use power-hungry, but very flexible software radios. Such base stations can be easily reprogrammed to process the signals used in new cellular standards. Many useful digital systems must translate from continuous analog signals to discrete digital signals. This causes quantization errors.
Quantization error can be reduced if the system stores enough digital data to represent the signal to the desired degree of fidelity. The Nyquist-Shannon sampling theorem provides an important guideline as to how much digital data is needed to accurately portray a given analog signal. In some systems, if a single piece of digital data is lost or misinterpreted, the meaning of large blocks of related data can completely change.
For example, a single-bit error in audio data stored directly as linear pulse code modulation causes, at worst, a single click.
Instead, many people use audio compression to save storage space and download time, even though a single bit error may cause a larger disruption. Because of the cliff effect , it can be difficult for users to tell if a particular system is right on the edge of failure, or if it can tolerate much more noise before failing. Digital fragility can be reduced by designing a digital system for robustness. For example, a parity bit or other error management method can be inserted into the signal path.
These schemes help the system detect errors, and then either correct the errors , or request retransmission of the data. 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. A logic gate is generally created from one or more electrically controlled switches, usually transistors but thermionic valves have seen historic use.
The output of a logic gate can, in turn, control or feed into more logic gates. Integrated circuits consist of multiple transistors on one silicon chip, and are the least expensive way to make large number of interconnected logic gates. Integrated circuits are usually interconnected on a printed circuit board which is a board which holds electrical components, and connects them together with copper traces.
Each logic symbol is represented by a different shape. Another form of digital circuit is constructed from lookup tables, many sold as " programmable logic devices ", though other kinds of PLDs exist. Lookup tables can perform the same functions as machines based on logic gates, but can be easily reprogrammed without changing the wiring.
This means that a designer can often repair design errors without changing the arrangement of wires. Therefore, in small volume products, programmable logic devices are often the preferred solution. They are usually designed by engineers using electronic design automation software.
When the volumes are medium to large, and the logic can be slow, or involves complex algorithms or sequences, often a small microcontroller is programmed to make an embedded system. These are usually programmed by software engineers. When only one digital circuit is needed, and its design is totally customized, as for a factory production line controller, the conventional solution is a programmable logic controller , or PLC.
These are usually programmed by electricians, using ladder logic. Engineers use many methods to minimize logic functions, in order to reduce the circuit's complexity. When the complexity is less, the circuit also has fewer errors and less electronics, and is therefore less expensive. The most widely used simplification is a minimization algorithm like the Espresso heuristic logic minimizer [ needs update ] within a CAD system, although historically, binary decision diagrams , an automated Quine—McCluskey algorithm , truth tables , Karnaugh maps , and Boolean algebra have been used.
Representations are crucial to an engineer's design of digital circuits. Some analysis methods only work with particular representations. The classical way to represent a digital circuit is with an equivalent set of logic gates. Another way, often with the least electronics, is to construct an equivalent system of electronic switches usually transistors. One of the easiest ways is to simply have a memory containing a truth table. The inputs are fed into the address of the memory, and the data outputs of the memory become the outputs.
For automated analysis, these representations have digital file formats that can be processed by computer programs. Most digital engineers are very careful to select computer programs "tools" with compatible file formats. To choose representations, engineers consider types of digital systems.
Most digital systems divide into " combinational systems " and " sequential systems. It is basically a representation of a set of logic functions, as already discussed. A sequential system is a combinational system with some of the outputs fed back as inputs. This makes the digital machine perform a "sequence" of operations. The simplest sequential system is probably a flip flop , a mechanism that represents a binary digit or " bit ". Sequential systems are often designed as state machines.
In this way, engineers can design a system's gross behavior, and even test it in a simulation, without considering all the details of the logic functions. Sequential systems divide into two further subcategories.
Synchronous sequential systems are made of well-characterized asynchronous circuits such as flip-flops, that change only when the clock changes, and which have carefully designed timing margins. The usual way to implement a synchronous sequential state machine is to divide it into a piece of combinational logic and a set of flip flops called a "state register.
The fastest rate of the clock is set by the most time-consuming logic calculation in the combinational logic. The state register is just a representation of a binary number.
If the states in the state machine are numbered easy to arrange , the logic function is some combinational logic that produces the number of the next state. As of , most digital logic is synchronous because it is easier to create and verify a synchronous design.
However, asynchronous logic is thought can be superior because its speed is not constrained by an arbitrary clock; instead, it runs at the maximum speed of its logic gates.
Building an asynchronous system using faster parts makes the circuit faster.
Nevertherless, most systems need circuits that allow external unsynchronized signals to enter synchronous logic circuits. These are inherently asynchronous in their design and must be analyzed as such.
Examples of widely used asynchronous circuits include synchronizer flip-flops, switch debouncers and arbiters. Asynchronous logic components can be hard to design because all possible states, in all possible timings must be considered. The usual method is to construct a table of the minimum and maximum time that each such state can exist, and then adjust the circuit to minimize the number of such states.
Then the designer must force the circuit to periodically wait for all of its parts to enter a compatible state this is called "self-resynchronization". Without such careful design, it is easy to accidentally produce asynchronous logic that is "unstable," that is, real electronics will have unpredictable results because of the cumulative delays caused by small variations in the values of the electronic components.
Many digital systems are data flow machines. These are usually designed using synchronous register transfer logic , using hardware description languages such as VHDL or Verilog.
In register transfer logic, binary numbers are stored in groups of flip flops called registers. The outputs of each register are a bundle of wires called a " bus " that carries that number to other calculations. A calculation is simply a piece of combinational logic. Each calculation also has an output bus, and these may be connected to the inputs of several registers. Sometimes a register will have a multiplexer on its input, so that it can store a number from any one of several buses.
Alternatively, the outputs of several items may be connected to a bus through buffers that can turn off the output of all of the devices except one. A sequential state machine controls when each register accepts new data from its input. Asynchronous register-transfer systems such as computers have a general solution.
In the s, some researchers discovered that almost all synchronous register-transfer machines could be converted to asynchronous designs by using first-in-first-out synchronization logic. In this scheme, the digital machine is characterized as a set of data flows.
In each step of the flow, an asynchronous "synchronization circuit" determines when the outputs of that step are valid, and presents a signal that says, "grab the data" to the stages that use that stage's inputs. It turns out that just a few relatively simple synchronization circuits are needed. The most general-purpose register-transfer logic machine is a computer.
This is basically an automatic binary abacus. The control unit of a computer is usually designed as a microprogram run by a microsequencer. A microprogram is much like a player-piano roll. Each table entry or "word" of the microprogram commands the state of every bit that controls the computer. The sequencer then counts, and the count addresses the memory or combinational logic machine that contains the microprogram.
The bits from the microprogram control the arithmetic logic unit , memory and other parts of the computer, including the microsequencer itself. A "specialized computer" is usually a conventional computer with special-purpose control logic or microprogram.
In this way, the complex task of designing the controls of a computer is reduced to a simpler task of programming a collection of much simpler logic machines. Almost all computers are synchronous. However, true asynchronous computers have also been designed. One example is the Aspida DLX core. Speed advantages have not materialized, because modern computer designs already run at the speed of their slowest component, usually memory.
These do use somewhat less power because a clock distribution network is not needed. An unexpected advantage is that asynchronous computers do not produce spectrally-pure radio noise, so they are used in some mobile-phone base-station controllers. They may be more secure in cryptographic applications because their electrical and radio emissions can be more difficult to decode. Computer architecture is a specialized engineering activity that tries to arrange the registers, calculation logic, buses and other parts of the computer in the best way for some purpose.
Computer architects have applied large amounts of ingenuity to computer design to reduce the cost and increase the speed and immunity to programming errors of computers.
An increasingly common goal is to reduce the power used in a battery-powered computer system, such as a cell-phone.
Many computer architects serve an extended apprenticeship as microprogrammers.
Digital circuits are made from analog components. The design must assure that the analog nature of the components doesn't dominate the desired digital behavior. Digital systems must manage noise and timing margins, parasitic inductances and capacitances, and filter power connections. Bad designs have intermittent problems such as "glitches", vanishingly fast pulses that may trigger some logic but not others, " runt pulses " that do not reach valid "threshold" voltages, or unexpected "undecoded" combinations of logic states.
Additionally, where clocked digital systems interface to analog systems or systems that are driven from a different clock, the digital system can be subject to metastability where a change to the input violates the set-up time for a digital input latch.
This situation will self-resolve, but will take a random time, and while it persists can result in invalid signals being propagated within the digital system for a short time. Since digital circuits are made from analog components, digital circuits calculate more slowly than low-precision analog circuits that use a similar amount of space and power.
However, the digital circuit will calculate more repeatably, because of its high noise immunity. On the other hand, in the high-precision domain for example, where 14 or more bits of precision are needed , analog circuits require much more power and area than digital equivalents.
To save costly engineering effort, much of the effort of designing large logic machines has been automated. The computer programs are called " electronic design automation tools" or just "EDA.
Simple truth table-style descriptions of logic are often optimized with EDA that automatically produces reduced systems of logic gates or smaller lookup tables that still produce the desired outputs.
The most common example of this kind of software is the Espresso heuristic logic minimizer. Most practical algorithms for optimizing large logic systems use algebraic manipulations or binary decision diagrams , and there are promising experiments with genetic algorithms and annealing optimizations. To automate costly engineering processes, some EDA can take state tables that describe state machines and automatically produce a truth table or a function table for the combinational logic of a state machine.
The state table is a piece of text that lists each state, together with the conditions controlling the transitions between them and the belonging output signals. It is common for the function tables of such computer-generated state-machines to be optimized with logic-minimization software such as Minilog.
Often, real logic systems are designed as a series of sub-projects, which are combined using a "tool flow. Tool flows for large logic systems such as microprocessors can be thousands of commands long, and combine the work of hundreds of engineers. Writing and debugging tool flows is an established engineering specialty in companies that produce digital designs.
The tool flow usually terminates in a detailed computer file or set of files that describe how to physically construct the logic. Often it consists of instructions to draw the transistors and wires on an integrated circuit or a printed circuit board.
Parts of tool flows are "debugged" by verifying the outputs of simulated logic against expected inputs. The test tools take computer files with sets of inputs and outputs, and highlight discrepancies between the simulated behavior and the expected behavior.