to circuits and electronics, in which the focus is on analog circuits alone.'' today's digital world requires a strong background in analog circuit principles as well. ANALOG & DIGITAL ELECTRONICS. Course No: PH Course Instructor: ❖ Dr. A.P. Vajpeyi. E-mail: [email protected] Room No: # PDF | On Jan 1, , D.K. Kaushik and others published Digital Electronics. Chapter 11 Digital to Analog and Analog to Digital Converters. Digital to.
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Daniel A. Steck, Analog and Digital Electronics, available online at echecs16.info teaching A Analog and Digital Circuits for Electronic Control System. Not surprisingly, digital electronics represents values with digits. The term digital is also used when referring to binary devices such as the circuitry that makes a. These teaching materials are organized in different files as follows: • echecs16.info: Here you can find out about the context in which these materials have been.
Analog and Digital Circuits Analog Electronics Most of the fundamental electronic components -- resistors , capacitors , inductors, diodes , transistors, and operational amplifiers -- are all inherently analog. Circuits built with a combination of solely these components are usually analog. Analog circuits are usually complex combinations of op amps, resistors, caps, and other foundational electronic components. This is an example of a class B analog audio amplifier. Analog circuits can be very elegant designs with many components, or they can be very simple, like two resistors combining to make a voltage divider. In general, though, analog circuits are much more difficult to design than those which accomplish the same task digitally. It takes a special kind of analog circuit wizard to design an analog radio receiver, or an analog battery charger; digital components exist to make those designs much simpler.
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.
Once the input data is believed correct, the design itself must still be verified for correctness. Some tool flows verify designs by first producing a design, and then scanning the design to produce compatible input data for the tool flow. If the scanned data matches the input data, then the tool flow has probably not introduced errors. The functional verification data are usually called "test vectors". The functional test vectors may be preserved and used in the factory to test that newly constructed logic works correctly.
However, functional test patterns don't discover common fabrication faults. Production tests are often designed by software tools called " test pattern generators ".
These generate test vectors by examining the structure of the logic and systematically generating tests for particular faults. Once a design exists, and is verified and testable, it often needs to be processed to be manufacturable as well. Modern integrated circuits have features smaller than the wavelength of the light used to expose the photoresist. Manufacturability software adds interference patterns to the exposure masks to eliminate open-circuits, and enhance the masks' contrast.
There are several reasons for testing a logic circuit. When the circuit is first developed, it is necessary to verify that the design circuit meets the required functional and timing specifications.
When multiple copies of a correctly designed circuit are being manufactured, it is essential to test each copy to ensure that the manufacturing process has not introduced any flaws.
A large logic machine say, with more than a hundred logical variables can have an astronomical number of possible states. Obviously, in the factory, testing every state is impractical if testing each state takes a microsecond, and there are more states than the number of microseconds since the universe began. This ridiculous-sounding case is typical. Large logic machines are almost always designed as assemblies of smaller logic machines.
To save time, the smaller sub-machines are isolated by permanently installed "design for test" circuitry, and are tested independently. One common test scheme known as "scan design" moves test bits serially one after another from external test equipment through one or more serial shift registers known as "scan chains". Serial scans have only one or two wires to carry the data, and minimize the physical size and expense of the infrequently used test logic.
After all the test data bits are in place, the design is reconfigured to be in "normal mode" and one or more clock pulses are applied, to test for faults e. Finally, the result of the test is shifted out to the block boundary and compared against the predicted "good machine" result. In a board-test environment, serial to parallel testing has been formalized with a standard called " JTAG " named after the "Joint Test Action Group" that made it.
Another common testing scheme provides a test mode that forces some part of the logic machine to enter a "test cycle. Several numbers determine the practicality of a system of digital logic: Engineers explored numerous electronic devices to get a favourable combination of these personalities. Since the bulk of a digital computer is simply an interconnected network of logic gates, the overall cost of building a computer correlates strongly with the price per logic gate.
In the s, the earliest digital logic systems were constructed from telephone relays because these were inexpensive and relatively reliable.
After that, electrical engineers always used the cheapest available electronic switches that could still fulfill the requirements. The earliest integrated circuits were a happy accident. They were constructed not to save money, but to save weight, and permit the Apollo Guidance Computer to control an inertial guidance system for a spacecraft.
To everyone's surprise, by the time the circuits were mass-produced, they had become the least-expensive method of constructing digital logic. Improvements in this technology have driven all subsequent improvements in cost. With the rise of integrated circuits , reducing the absolute number of chips used represented another way to save costs.
The goal of a designer is not just to make the simplest circuit, but to keep the component count down. Sometimes this results in more complicated designs with respect to the underlying digital logic but nevertheless reduces the number of components, board size, and even power consumption.
A major motive for reducing component count on printed circuit boards is to reduce the manufacturing defect rate and increase reliability, as every soldered connection is a potentially bad one, so the defect and failure rates tend to increase along with the total number of component pins. For example, in some logic families, NAND gates are the simplest digital gate to build.
All other logical operations can be implemented by NAND gates. If a circuit already required a single NAND gate, and a single chip normally carried four NAND gates, then the remaining gates could be used to implement other logical operations like logical and. This could eliminate the need for a separate chip containing those different types of gates. The "reliability" of a logic gate describes its mean time between failure MTBF.
Digital machines often have millions of logic gates. Also, most digital machines are "optimized" to reduce their cost. The result is that often, the failure of a single logic gate will cause a digital machine to stop working. It is possible to design machines to be more reliable by using redundant logic which will not malfunction as a result of the failure of any single gate or even any two, three, or four gates , but this necessarily entails using more components, which raises the financial cost and also usually increases the weight of the machine and may increase the power it consumes.
Digital machines first became useful when the MTBF for a switch got above a few hundred hours. Even so, many of these machines had complex, well-rehearsed repair procedures, and would be nonfunctional for hours because a tube burned-out, or a moth got stuck in a relay. Modern transistorized integrated circuit logic gates have MTBFs greater than 82 billion hours 8.
Fanout describes how many logic inputs can be controlled by a single logic output without exceeding the electrical current ratings of the gate outputs.
Modern electronic logic gates using CMOS transistors for switches have fanouts near fifty, and can sometimes go much higher.
The "switching speed" describes how many times per second an inverter an electronic representation of a "logical not" function can change from true to false and back. Faster logic can accomplish more operations in less time.
Design started with relays. Relay logic was relatively inexpensive and reliable, but slow. Occasionally a mechanical failure would occur. Fanouts were typically about 10, limited by the resistance of the coils and arcing on the contacts from high voltages. Later, vacuum tubes were used.
These were very fast, but generated heat, and were unreliable because the filaments would burn out. Fanouts were typically In the s, special "computer tubes" were developed with filaments that omitted volatile elements like silicon.
These ran for hundreds of thousands of hours. The first semiconductor logic family was resistor—transistor logic. Leave this field empty.
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