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A digital circuit that acts as a binary clock, hand-wired on a series of breadboards
A digital circuit that acts as a binary clock, hand-wired on a series of breadboards

Digital electronics are electronics systems that use digital signals. A binary clock is a Clock which displays traditional Sexagesimal Time in a binary format A breadboard ( solderless breadboard, protoboard, plugboard) is a reusable Solderless device used to build a (generally temporary Prototype Electronics refers to the flow of charge (moving Electrons through Nonmetal conductors (mainly Semiconductors, whereas electrical The term digital signal is used to refer to more than one concept Digital electronics are representations of Boolean algebra and are used in computers, mobile phones, and other consumer products. Boolean algebra (or Boolean logic) is a logical calculus of truth values, developed by George Boole in the late 1830s A computer is a Machine that manipulates data according to a list of instructions. ( A consumer product is generally any tangible personal property for sale and that is used for personal family or household purposes

Digital electronics or any digital circuit are usually made from large assemblies of logic gates, simple electronic representations of Boolean logic functions. A logic gate performs a logical operation on one or more logic inputs and produces a single logic output

To most electronic engineers, the terms "digital circuit", "digital system" and "logic" are interchangeable in the context of digital circuits. Logic is the study of the principles of valid demonstration and Inference.


Contents

Advantages

The usual advantages of digital circuits when compared to analog circuits are:

Robustness

One of the primary advantages of digital electronics is its robustness. Digital electronics are robust because if the noise is less than the noise margin then the system performs as if there were no noise at all. In Electrical engineering, noise margin is the amount by which a signal exceeds the minimum amount for proper operation Therefore, digital signals can be regenerated to achieve lossless data transmission, within certain limits.

Analog signal transmission and processing, by contrast, always introduces noise.

Disadvantages

In some cases, digital circuits use more energy than analog circuits to accomplish the same tasks, thus producing more heat as well. 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. Generally an amplifier or simply amp, is any device that changes usually increases the amplitude of a signal. A tuner is a circuit module or free-standing equipment which detects Radio-frequency (RF signals usually of low Amplitude and amplifies them Radio is the transmission of signals by Modulation of electromagnetic waves with frequencies below those of visible Light. However, a base station has grid power and can use power-hungry, but very flexible software radios. A Software-Defined Radio (SDR system is a Radio communication system where components that have typically been implemented in hardware (i Such base stations can be easily reprogrammed to process the signals used in new cellular standards.

Digital circuits are sometimes more expensive, especially in small quantities.

The sensed world is analog, and signals from this world are analog quantities. For example, light, temperature, sound, electrical conductivity, electric and magnetic fields are analog. Most 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. Fidelity is a notion that at its most abstract level implies a truthful connection to a source or sources The Nyquist-Shannon sampling theorem provides an important guideline as to how much digital data is needed to accurately portray a given analog signal. The Nyquist–Shannon sampling theorem is a fundamental result in the field of Information theory, in particular Telecommunications and Signal processing

Fragility

Digital systems can be fragile, in that if a single piece of digital data is lost or misinterpreted, the meaning of large blocks of related data can completely change.

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. Error detection If an odd number of bits (including the parity bit are changed in transmission of a set of bits then parity bit will be incorrect and will thus indicate In Mathematics, Computer science, Telecommunication, and Information theory, error detection and correction has great practical importance in These schemes help the system detect errors, and then either correct the errors, or at least ask for a new copy of the data. In Mathematics, Computer science, Telecommunication, and Information theory, error detection and correction has great practical importance in In a state-machine, the state transition logic can be designed to catch unused states and trigger a reset sequence or other error recovery routine. Some further examples:

Analog issues in digital circuits

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. Electronic filters are Electronic circuits which perform Signal processing functions specifically intended to remove unwanted signal components and/or enhance wanted

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. In Digital circuits a runt pulse is a narrow pulse that due to non-zero rise and fall times of the signal does not reach a valid high or low

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.

Construction

A digital circuit is often constructed from small electronic circuits called logic gates. A logic gate performs a logical operation on one or more logic inputs and produces a single logic output Each logic gate represents a function of boolean logic. Boolean logic is a complete system for Logical operations It was named after George Boole, who first defined an algebraic system of A logic gate is an arrangement of electrically controlled switches.

The output of a logic gate is an electrical flow or voltage, that can, in turn, control more logic gates. Electric current is the flow (movement of Electric charge. The SI unit of electric current is the Ampere. At a point in space the electric potential is the Potential energy per unit of charge that is associated with a static (time-invariant Electric field

Logic gates often use the fewest number of transistors in order to reduce their size, power consumption and cost, and increase their reliability.

Integrated circuits, are the least expensive way to make logic gates in large volumes. Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside Integrated circuits are usually designed by engineers using electronic design automation software (See below for more information). Electronic design automation ( EDA) is the category of tools for designing and producing electronic systems ranging from

Another form of digital circuit is constructed from lookup tables, (many sold as "programmable logic devices", though other kinds of PLDs exist). A programmable logic device or PLD is an electronic component used to build reconfigurable Digital circuits Unlike a Logic gate, which has a 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 (See below for more information). Electronic design automation ( EDA) is the category of tools for designing and producing electronic systems ranging from

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. A microcontroller (also MCU or µC is a functional Computer system-on-a- chip. Computer programs (also software programs, or just programs) are instructions for a Computer. An embedded system is a special-purpose Computer system designed to perform one or a few dedicated functions often with Real-time computing constraints These are usually programmed by software engineers. Software engineering is the application of a systematic disciplined quantifiable approach to the development operation and maintenance of Software.

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. A programmable logic controller ( PLC) or programmable controller is a Digital computer used for Automation of industrial processes such as These are usually programmed by electricians, using ladder logic. Ladder logic is a philosophy of drawing electrical logic schematics

Structure of digital systems

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 within a CAD system, although historically, binary decision diagrams, an automated Quine–McCluskey algorithm, truth tables, Karnaugh Maps, and Boolean algebra have been used. The Espresso logic minimizer is a widely used computer program using heuristic and specific algorithms for efficiently reducing the complexity of digital electronic gate circuits A binary decision diagram ( BDD) like a Negation normal form (NNF or a Propositional directed acyclic graph (PDAG is a Data structure that The Quine–McCluskey algorithm (or the method of prime implicants) is a method used for minimization of Boolean functions which was developed by W A truth table is a Mathematical table used in Logic — specifically in connection with Boolean algebra, Boolean functions and Propositional The Karnaugh map, also known as a Veitch diagram ( KV-map or K-map for short is a tool to facilitate the simplification of Boolean algebra Boolean algebra (or Boolean logic) is a logical calculus of truth values, developed by George Boole in the late 1830s

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. A logic gate performs a logical operation on one or more logic inputs and produces a single logic output Another way, often with the least electronics, is to construct an equivalent system of electronic switches (usually transistors). In Electronics, a transistor is a Semiconductor device commonly used to amplify or switch electronic signals One of the easiest ways is to simply have a memory containing a truth table. A truth table is a Mathematical table used in Logic — specifically in connection with Boolean algebra, Boolean functions and Propositional 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 "combinatorial systems" and "sequential systems. " A combinatorial system always presents the same output when given the same inputs. It is basically a representation of a set of logic functions, as already discussed.

A sequential system is a combinatorial 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". In Digital circuits a flip-flop is a term referring to an Electronic circuit (a Bistable Multivibrator) that has two stable states and thereby The binary numeral system, or base-2 number system, is a Numeral system that represents numeric values using two symbols usually 0 and 1. A bit is a binary digit, taking a value of either 0 or 1 Binary digits are a basic unit of Information storage and communication

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 change state all at once, when a "clock" signal changes state. A synchronous circuit is a Digital circuit in which the parts are synchronized by a Clock signal. "Asynchronous" sequential systems propagate changes whenever inputs change. In a Synchronous system, operations are coordinated under the centralized control of a fixed-rate Clock signal or several clocks 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 divide it into a piece of combinatorial logic and a set of flip flops called a "state register. " Each time a clock signal ticks, the state register captures the feedback generated from the previous state of the combinatorial logic, and feeds it back as an unchanging input to the combinatorial part of the state machine. The fastest rate of the clock is set by the most time-consuming logic calculation in the combinatorial 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 combinatorial logic that produces the number of the next state.

In comparison, asynchronous systems are very 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, and 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. Certain circuits (such as the synchronizer flip-flops, switch debouncers, and the like which allow external unsynchronized signals to enter synchronous logic circuits) are inherently asynchronous in their design and must be analyzed as such. A switch is a mechanical device used to connect and disconnect an electric Circuit at will

As of 2005, almost all digital machines are synchronous designs because it is much easier to create and verify a synchronous design -- the software currently used to simulate digital machines does not yet handle asynchronous designs. However, asynchronous logic is thought to be superior, if it can be made to work, because its speed is not constrained by an arbitrary clock; instead, it simply runs at the maximum speed permitted by the propagation rates of the logic gates from which it is constructed. Building an asynchronous circuit using faster parts implicitly makes the circuit "go" faster.

More generally, 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 Integrated circuit design, Register Transfer Level ( RTL) description is a way of describing the operation of a synchronous Digital circuit In the Semiconductor and electronic design industry Verilog is a Hardware description language (HDL used to model electronic systems.

In register transfer logic, binary numbers are stored in groups of flip flops called registers. The binary numeral system, or base-2 number system, is a Numeral system that represents numeric values using two symbols usually 0 and 1. A number is an Abstract object, tokens of which are Symbols used in Counting and measuring. In Computer architecture, a processor register is a small amount of storage available on the CPU whose contents can be accessed more quickly than storage The outputs of each register are a bundle of wires called a "bus" that carries that number to other calculations. In Computer architecture, a bus is a subsystem that transfers data between computer components inside a Computer or between computers A calculation is simply a piece of combinatorial 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. In Electronics, a multiplexer or mux ( occasionally the term muldex is also found for a combination multiplexer-demultiplexer 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. In digital Electronics three-state, tri-state, or 3-state logic allows output ports to have a value of logical 0 1 or Hi-Z A sequential state machine controls when each register accepts new data from its input.

In the 1980s, 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. A computer is a Machine that manipulates data according to a list of instructions. This is basically an automatic binary abacus. This article is about a self-operating machine For other uses of Automaton see Automaton (disambiguation or Automata (disambiguation. The binary numeral system, or base-2 number system, is a Numeral system that represents numeric values using two symbols usually 0 and 1. An abacus, also called a counting frame, is a calculating tool used primarily by Asians for performing arithmetic processes The control unit of a computer is usually designed as a microprogram run by a microsequencer. A control unit in general is a central (or sometimes distributed but clearly distinguishable part of whatsoever machinery that controls its operation provided that Microprogramming (ie writing microcode) is a method that can be employed to implement Machine instructions in a CPU relatively easily often using less In Computer architecture and Engineering, a sequencer or microsequencer is a part of the Control unit of a CPU. 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 combinatorial 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. In Computing, an arithmetic logic unit ( ALU) is a Digital circuit that performs Arithmetic and Logical operations In Psychology, memory is an organism's ability to store retain and subsequently retrieve information In Computer architecture and Engineering, a sequencer or microsequencer is a part of the Control unit of a CPU.

In this way, the complex task of designing the controls of a computer is reduced to a simpler task of programming a relatively independent collection of much simpler logic machines.

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. In Computer engineering, computer architecture is the conceptual design and fundamental operational structure of a Computer system 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.

"Specialized computers" are usually a conventional computer with a special-purpose microprogram.

Automated design tools

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. Electronic design automation ( EDA) is the category of tools for designing and producing electronic systems ranging from "

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. The Espresso logic minimizer is a widely used computer program using heuristic and specific algorithms for efficiently reducing the complexity of digital electronic gate circuits

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. The Quine–McCluskey algorithm (or the method of prime implicants) is a method used for minimization of Boolean functions which was developed by W A binary decision diagram ( BDD) like a Negation normal form (NNF or a Propositional directed acyclic graph (PDAG is a Data structure that A genetic algorithm (GA is a Search technique used in Computing to find exact or Approximate solutions to optimization and Search Simulated annealing (SA is a generic probabilistic Meta-algorithm for the Global optimization problem namely locating a good approximation to the

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 combinatorial part of a state machine. In Automata theory and Sequential logic, a state transition table is a table showing what state (or states in the case of a nondeterministic finite automaton A truth table is a Mathematical table used in Logic — specifically in connection with Boolean algebra, Boolean functions and Propositional 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. The Espresso logic minimizer is a widely used computer program using heuristic and specific algorithms for efficiently reducing the complexity of digital electronic gate circuits

Often, real logic systems are designed as a series of sub-projects, which are combined using a "tool flow. " The tool flow is usually a "script," a simplified computer language that can invoke the software design tools in the right order.

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. In Electronics, a transistor is a Semiconductor device commonly used to amplify or switch electronic signals Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside A printed circuit board, or PCB, is used to mechanically support and electrically connect Electronic components using conductive pathways or traces

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. ATPG (acronym for both A utomatic T est P attern G eneration and A utomatic T est P attern G enerator is " These generate test vectors by examining the structure of the logic and systematically generating tests for particular faults. This way the fault coverage can closely approach 100%, provided the design is properly made testable (see next section). Fault coverage refers to the percentage of some type of Fault that can be detected during the test of an Electronic system, usually an integrated circuit

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 enhace the masks' resolution and contrast.

Design for testability

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. Unfortunately, this ridiculous-sounding case is typical.

Fortunately, 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". In Digital circuits a shift register is a group of flip flops set up in a linear fashion which have their inputs and outputs connected together in such a way that the 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. g. stuck-at low or stuck-at high) and capture the test result into flip-flops and/or latches in the scan shift register(s). In Digital circuits a flip-flop is a term referring to an Electronic circuit (a Bistable Multivibrator) that has two stable states and thereby 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 proposed it). Joint Test Action Group ( JTAG) is the usual name used for the IEEE 1149

Another common testing scheme provides a test mode that forces some part of the logic machine to enter a "test cycle. " The test cycle usually exercises large independent parts of the machine.

Trade-offs

Several numbers determine the practicality of a system of digital logic. Engineers explored numerous electronic devices to get an ideal combination of fanout, speed, low cost and reliability.

The cost of a logic gate is crucial. In the 1930s, the earliest digital logic systems were constructed from telephone relays because these were inexpensive and relatively reliable. The 1930s were described as an abrupt shift to more radical and conservative lifestyles as countries were struggling to find a solution to the Great Depression. After that, engineers always used the cheapest available electronic switches that could still fulfill the requirements.

The earliest integrated circuits were a happy accident. Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside 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. An Inertial Navigation System (INS is a Navigation aid that uses a Computer and motion sensors to continuously track the position orientation and Velocity The first integrated circuit logic gates cost nearly $50 (in 1960 dollars, when an engineer earned $10,000/year). 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. Microchipsjpg|right|thumb|200px|Microchips ( EPROM memory with a transparent window showing the integrated circuit inside The goal of a designer is not just to make the simplest circuit, but to keep the component count down. Sometimes this results in slightly more complicated designs with respect to the underlying digital logic but nevertheless reduces the number of components, board size, and even power consumption.

For example, in some logic families, NAND gates are the simplest digital gate to build. Definition The NAND operation is a Logical operation on two Logical values typically the values of two Propositions that produces a value All other logical operations can be implemented by NAND gates. Definition The NAND operation is a Logical operation on two Logical values typically the values of two Propositions that produces a value 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. Definition The NAND operation is a Logical operation on two Logical values typically the values of two Propositions that produces a value Definition The NAND operation is a Logical operation on two Logical values typically the values of two Propositions that produces a value In Logic and/or Mathematics, logical conjunction or and is a two-place Logical operation that results in a value of true if both of 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.

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 of nearly a trillion (1x10^12) hours, and need them because they have so many logic gates.

Fanout describes how many logic inputs can be controlled by a single logic output. The minimum practical fanout is about five. Modern electronic logic using CMOS transistors for switches have fanouts near fifty, and can sometimes go much higher. Complementary metal–oxide–semiconductor ( CMOS) (pronounced "see-moss" siːmɔːs ˈsiːmɒs is a major class of Integrated circuits CMOS technology In Electronics, a transistor is a Semiconductor device commonly used to amplify or switch electronic signals

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. Digital logic first became useful when switching speeds got above fifty hertz, because that was faster than a team of humans operating mechanical calculators. The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. Modern electronic digital logic routinely switches at five gigahertz (5x109 hertz), and some laboratory systems switch at more than a terahertz (1x1012 hertz). The hertz (symbol Hz) is a measure of Frequency, informally defined as the number of events occurring per Second. Electromagnetic waves sent at terahertz frequencies, known as terahertz radiation, submillimeter radiation, terahertz waves, terahertz

Logic families

Design started with relays. A relay is an electrical Switch that opens and closes under the control of another Electrical circuit. Relay logic was relatively inexpensive and reliable, but slow. Occasionally a mechanical failure would occur. Most famously, a moth was caught in an early relay computer, and gave rise to the terms "bug in the program", and "Debugging. " Fanouts were typically about ten, limited by the resistance of the coils and arcing on the contacts from high voltages.

Later, vacuum tubes were used. This article is about the electronic device not an evacuated pipe used for experiments in Free-fall. These were very fast, but generated heat, and were unreliable because the filaments would burn out. Fanouts were typically five to seven, limited by the heating from the tubes' current. In the 1950s, 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. A semiconductor' is a Solid material that has Electrical conductivity in between a conductor and an insulator; it can vary over that Resistor–transistor logic ( RTL) is a class of Digital circuits built using Resistors as the input network and Bipolar junction transistors This was a thousand times more reliable than tubes, ran cooler, and used less power, but had a very low fan-in of three. Fan-in is the number of inputs of an electronic Logic gate. For instance the 'fan-in' for the AND gate shown below is 3 Diode-transistor logic improved the fanout up to about seven, and reduced the power. Some DTL designs used two power-supplies with alternating layers of NPN and PNP transistors to increase the fanout.

Transistor transistor logic (TTL) was a great improvement over these. Transistor–transistor logic ( TTL) is a class of Digital circuits built from Bipolar junction transistors (BJT and Resistors It is called In early devices, fanout improved to ten, and later variations reliably achieved twenty. TTL was also fast, with some variations achieving switching times as low as twenty nanoseconds. TTL is still used in some designs.

Another contender was emitter coupled logic. In electronics emitter-coupled logic, or ECL, is a Logic family in which current is steered through bipolar transistors to implement Logic This is very fast but uses a lot of power. It's now used mostly in radio-frequency circuits.

Modern integrated circuits mostly use variations of CMOS, which is acceptably fast, very small and uses very little power. Complementary metal–oxide–semiconductor ( CMOS) (pronounced "see-moss" siːmɔːs ˈsiːmɒs is a major class of Integrated circuits CMOS technology Fanouts of forty or more are possible, with some speed penalty.

Non-electronic logic

It is possible to construct non-electronic digital mechanisms. In principle, any technology capable of representing discrete states and representing logic operations could be used to build mechanical logic. Danny Hillis, co-author of The Connection Machine, once built a working computer from Tinker toys, string, a brick, and a sharpened pencil, which is supposed to be in the Houston Museum of Natural Science. William Daniel "Danny" Hillis (born September 25, 1956, in Baltimore, Maryland) is an American Inventor, The Connection Machine was a series of Supercomputers that grew out of Danny Hillis's research in the early 1980s at MIT on alternatives to the traditional The Tinkertoy Construction Set was created in 1914&mdashone year after the A The Houston Museum of Natural Science is a Science museum located on the northern border of Hermann Park in Houston, Texas, USA.

Hydraulic, pneumatic and mechanical versions of logic gates exist and are used in situations where electricity cannot be used. The first two types are considered under the heading of fluidics. Fluidics (also known as Fluidic logic) is the use of a Fluid or compressible medium to perform analog or Digital operations similar to those One application of fluidic logic is in military hardware that is likely to be exposed to a nuclear electromagnetic pulse (nuclear EMP, or NEMP) that would destroy electrical circuits. The term electromagnetic pulse ( EMP) has the following meanings Electromagnetic radiation from an Explosion (especially a Nuclear

Mechanical logic is frequently used in inexpensive controllers, such as those in washing machines. Famously, the first computer design, by Charles Babbage, was designed to use mechanical logic. Mechanical logic might also be used in very small computers that could be built by nanotechnology. Nanotechnology, sometimes shortened to nanotech, refers to a field of Applied science whose theme is the control of matter on an Atomic and Molecular

Another example is that if two particular enzymes are required to prevent the construction of a particular protein, this is the equivalent of a biological "NAND" gate.

Recent developments

The discovery of superconductivity has enabled the development of Rapid Single Flux Quantum (RSFQ) circuit technology, which uses Josephson junctions instead of transistors. Superconductivity is a phenomenon occurring in certain Materials generally at very low Temperatures characterized by exactly zero electrical resistance In Electronics, rapid single flux quantum ( RSFQ) is a Digital electronics technology that relies on quantum effects in Superconducting materials The Josephson effect is the phenomenon of current flow across two weakly coupled Superconductors, separated by a very thin insulating barrier Most recently, attempts are being made to construct purely optical computing systems capable of processing digital information using nonlinear optical elements. An optical computer is a computer that uses light instead of electricity (i This article describes the use of the term nonlinearity in mathematics

Branch pages

Electronics - Combinatorial logic - Boolean algebra - Fuzzy electronics - Logic analyzer - Logic gate - Glitch - Ringing - Programmable logic device - Reconfigurable system - Register

See also

External links

References

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