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Standard Cell
In semiconductor design, STANDARD CELL methodology is a method of designing application-specific integrated circuits (ASICs) with mostly digital-logic features. Standard cell
Standard cell
methodology is an example of design abstraction, whereby a low-level very-large-scale integration ( VLSI ) layout is encapsulated into an abstract logic representation (such as a N AND gate
AND gate
). Cell-based methodology — the general class to which standard cells belong — makes it possible for one designer to focus on the high-level (logical function) aspect of digital design, while another designer focuses on the implementation (physical) aspect. Along with semiconductor manufacturing advances, standard cell methodology has helped designers scale ASICs from comparatively simple single-function ICs (of several thousand gates), to complex multi-million gate system-on-a-chip (SoC) devices. CONTENTS * 1 Construction of a standard cell * 2 Library * 3 Application of standard cell * 3.1 Synthesis * 3.2 Placement * 4 Routing * 4.1 DRC/LVS * 5 Other cell-based methodologies * 6 Complexity measure * 7 See also * 8 External links CONSTRUCTION OF A STANDARD CELLA standard cell is a group of transistor and interconnect structures that provides a boolean logic function (e.g., AND , OR , XOR
XOR
, XNOR , inverters) or a storage function (flipflop or latch)
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Dielectric
A DIELECTRIC (or DIELECTRIC MATERIAL) is an electrical insulator that can be polarized by an applied electric field . When a dielectric is placed in an electric field, electric charges do not flow through the material as they do in an electrical conductor , but only slightly shift from their average equilibrium positions causing DIELECTRIC POLARIZATION. Because of dielectric polarization, positive charges are displaced toward the field and negative charges shift in the opposite direction. This creates an internal electric field that reduces the overall field within the dielectric itself. If a dielectric is composed of weakly bonded molecules, those molecules not only become polarized, but also reorient so that their symmetry axes align to the field. The study of dielectric properties concerns storage and dissipation of electric and magnetic energy in materials. Dielectrics are important for explaining various phenomena in electronics , optics , solid-state physics , and cell biophysics
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Weston Cell
The WESTON CELL is a wet-chemical cell that produces a highly stable voltage suitable as a laboratory standard for calibration of voltmeters . Invented by Edward Weston in 1893, it was adopted as the International Standard for EMF between 1911 and 1990. CONTENTS * 1 Chemistry * 2 Characteristics * 3 References * 4 Literature * 5 External links CHEMISTRYThe anode is an amalgam of cadmium with mercury with a cathode of pure mercury over which a paste of mercurous sulfate and mercury is placed. The electrolyte is a saturated solution of cadmium sulfate , and the depolarizer is a paste of mercurous sulfate . As shown in the illustration, the cell is set up in an H-shaped glass vessel with the cadmium amalgam in one leg and the pure mercury in the other. Electrical connections to the cadmium amalgam and the mercury are made by platinum wires fused through the lower ends of the legs. Anode reaction: Cd(s) → Cd2+(aq) + 2e− Cathode reaction: (Hg+)2SO42−(s) + 2e− → 2Hg(l) + SO42−(aq) Reference cells must be applied in such a way that no current is drawn from them. CHARACTERISTICSThe original design was a saturated cadmium cell producing a 7000101863800000000♠1.018638 V reference and had the advantage of having a lower temperature coefficient than the previously used Clark cell . One of the great advantages of the Weston normal cell is its small change of electromotive force with change of temperature
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Clark Cell
The CLARK CELL, invented by English engineer Josiah Latimer Clark in 1873, is a wet-chemical cell (colloquially: battery) that produces a highly stable voltage . In 1893, the output of the Clark cell
Clark cell
at 15 °C was defined by the International Electrical Congress as 1.434 volts, and this definition became law in the United States in 1894. This definition was later supplanted by one based on the Weston cell
Weston cell
. CONTENTS * 1 Chemistry * 2 Construction * 2.1 Original cell * 2.2 H-form cell * 3 Characteristics * 4 Sources * 5 References CHEMISTRYClark cells use a zinc , or zinc amalgam , anode and a mercury cathode in a saturated aqueous solution of zinc sulfate , with a paste of mercurous sulfate as depolarizer . CONSTRUCTIONORIGINAL CELLClark's original cell was set up in a glass jar in a similar way to a gravity Daniell cell
Daniell cell
. The copper cathode was replaced by a pool of mercury at the bottom of the jar. Above this was the mercurous sulfate paste and, above that, the zinc sulfate solution. A short zinc rod dipped into the zinc sulfate solution. The zinc rod was supported by a cork with two holes — one for the zinc rod and the other for a glass tube reaching to the bottom of the cell. A platinum wire, fused into the glass tube, made contact with the mercury pool. When complete, the cell was sealed with a layer of marine glue
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Application-specific Integrated Circuit
An APPLICATION-SPECIFIC INTEGRATED CIRCUIT (ASIC) /ˈeɪsɪk/ , is an integrated circuit (IC) customized for a particular use, rather than intended for general-purpose use. For example, a chip designed to run in a digital voice recorder or a high-efficiency Bitcoin miner is an ASIC. Application-specific standard products (ASSPs) are intermediate between ASICs and industry standard integrated circuits like the 7400 or the 4000 series . As feature sizes have shrunk and design tools improved over the years, the maximum complexity (and hence functionality) possible in an ASIC has grown from 5,000 gates to over 100 million. Modern ASICs often include entire microprocessors , memory blocks including ROM , RAM , EEPROM , flash memory and other large building blocks. Such an ASIC is often termed a SoC (system-on-chip ). Designers of digital ASICs often use a hardware description language (HDL), such as Verilog or VHDL , to describe the functionality of ASICs. Field-programmable gate arrays (FPGA) are the modern-day technology for building a breadboard or prototype from standard parts; programmable logic blocks and programmable interconnects allow the same FPGA to be used in many different applications. For smaller designs or lower production volumes, FPGAs may be more cost effective than an ASIC design even in production
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VLSI
VERY-LARGE-SCALE INTEGRATION (VLSI) is the process of creating an integrated circuit (IC) by combining thousands of transistors into a single chip. VLSI began in the 1970s when complex semiconductor and communication technologies were being developed. The microprocessor is a VLSI device. Before the introduction of VLSI technology most ICs had a limited set of functions they could perform. An electronic circuit might consist of a CPU , ROM , RAM and other glue logic . VLSI lets IC designers add all of these into one chip. A VLSI integrated-circuit die CONTENTS * 1 History * 2 Developments * 3 Structured design * 4 Struggles * 5 See also * 6 References * 7 Further reading * 8 External links HISTORYThe History of the transistor dates to the mid-1920s when several inventors attempted devices that were intended to control current in solid-state diodes and convert them into triodes. Success came after World War II, when the use of silicon and germanium crystals as radar detectors led to improvements in fabrication and theory. Scientists who had worked on radar returned to solid-state device development. With the invention of transistors at Bell Labs in 1947, the field of electronics shifted from vacuum tubes to solid-state devices. With the small transistor at their hands, electrical engineers of the 1950s saw the possibilities of constructing far more advanced circuits
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Integrated Circuit Layout
INTEGRATED CIRCUIT LAYOUT, also known IC LAYOUT, IC MASK LAYOUT, or MASK DESIGN, is the representation of an integrated circuit in terms of planar geometric shapes which correspond to the patterns of metal , oxide , or semiconductor layers that make up the components of the integrated circuit. When using a standard process—where the interaction of the many chemical, thermal, and photographic variables is known and carefully controlled—the behaviour of the final integrated circuit depends largely on the positions and interconnections of the geometric shapes. Using a computer-aided layout tool, the layout engineer—or layout technician—places and connects all of the components that make up the chip such that they meet certain criteria—typically: performance, size, density, and manufacturability. This practice is often subdivided between two primary layout disciplines: Analog and digital. The generated layout must pass a series of checks in a process known as physical verification. The most common checks in this verification process are * design rule checking (DRC) , * layout versus schematic (LVS) , * parasitic extraction , * antenna rule checking , and * electrical rule checking (ERC) .When all verification is complete, the data is translated into an industry-standard format, typically GDSII
GDSII
, and sent to a semiconductor foundry
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Negated AND Gate
In digital electronics , a NAND GATE (NEGATIVE-AND) is a logic gate which produces an output which is false only if all its inputs are true; thus its output is complement to that of the AND gate
AND gate
. A LOW (0) output results only if both the inputs to the gate are HIGH (1); if one or both inputs are LOW (0), a HIGH (1) output results. It is made using transistors and junction diodes. By De Morgan\'s theorem , AB=A+B, and thus a N AND gate
AND gate
is equivalent to inverters followed by an OR gate
OR gate
. The N AND gate
AND gate
is significant because any boolean function can be implemented by using a combination of NAND gates. This property is called functional completeness . It shares this property with the NOR gate . Digital systems employing certain logic circuits take advantage of NAND's functional completeness. The function NAND(a1, a2, ..., an) is logically equivalent to NOT(a1 AND a2 AND ... AND an). CONTENTS * 1 Symbols * 2 Hardware description and pinout * 3 Implementations * 3.1 Alternatives * 4 See also * 5 References * 6 External links SYMBOLSThere are three symbols for NAND gates: the MIL/ ANSI
ANSI
symbol, the IEC symbol and the deprecated DIN
DIN
symbol sometimes found on old schematics. For more information see logic gate symbols
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Semiconductor Manufacturing
SEMICONDUCTOR DEVICE FABRICATION is the process used to create the integrated circuits that are present in everyday electrical and electronic devices. It is a multiple-step sequence of photo lithographic and chemical processing steps during which electronic circuits are gradually created on a wafer made of pure semiconducting material. Silicon
Silicon
is almost always used, but various compound semiconductors are used for specialized applications. The entire manufacturing process, from start to packaged chips ready for shipment, takes six to eight weeks and is performed in highly specialized facilities referred to as fabs . CONTENTS * 1 History * 2 Wafers * 3 Processing * 3.1 Front-end-of-line (FEOL) processing * 3.1.1 Gate oxide and implants * 3.2 Back-end-of-line (BEOL) processing * 3.2.1 Metal layers * 3.2.2 Interconnect * 4 Wafer test * 5 Device test * 6 Die preparation
Die preparation
* 7 Packaging * 8 List of steps * 9 Hazardous materials * 10 See also * 11 References * 12 Further reading * 13 External links HISTORY Main article: Integrated circuit
Integrated circuit
When feature widths were far greater than about 10 micrometres , purity was not the issue that it is today in device manufacturing. As devices became more integrated, cleanrooms became even cleaner
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System On A Chip
A SYSTEM ON A CHIP or SYSTEM ON CHIP (SOC or SOC) is an integrated circuit (also known as an "IC" or "chip") that integrates all components of a computer or other electronic systems. It may contain digital , analog , mixed-signal , and often radio-frequency functions—all on a single substrate . SoCs are very common in the mobile computing market because of their low power-consumption. A typical application is in the area of embedded systems . SoC integrates a microcontroller (or microprocessor ) with advanced peripherals like graphics processing unit (GPU), Wi-Fi module, or coprocessor . If the definition of a microcontroller is a system that integrates a microprocessor with peripheral circuits and memory, the SoC is to a microcontroller what a microcontroller is to processors , remembering that the SoC does not necessarily contain built-in memory. In general, there are three distinguishable types of SoCs. SoCs built around a microcontroller, SoCs built around a microprocessor (this type can be found in mobile phones), and specialized SoCs designed for specific applications that do not fit into the above two categories. A separate category may be Programmable SoC ( PSoC
PSoC
), where some of the internal elements are not predefined and can be programmable in a manner analogous to the FPGA or CPLD
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AND Gate
The AND GATE is a basic digital logic gate that implements logical conjunction - it behaves according to the truth table to the right. A HIGH output (1) results only if both the inputs to the AND gate
AND gate
are HIGH (1). If neither or only one input to the AND gate
AND gate
is HIGH, a LOW output results. In another sense, the function of AND effectively finds the minimum between two binary digits, just as the OR function finds the maximum between two binary digits. Therefore, the output is always 0, except when all the inputs are 1. CONTENTS * 1 Symbols * 2 Implementations * 2.1 Alternatives * 3 IC package * 4 See also * 5 References SYMBOLSThere are three symbols for AND gates: the American (ANSI or 'military') symbol and the IEC ('European' or 'rectangular') symbol, as well as the deprecated DIN symbol. For more information see Logic Gate Symbols . MIL/ANSI Symbol IEC Symbol DIN SymbolThe AND gate
AND gate
with inputs A and B and output C implements the logical expression C = A B {displaystyle C=Acdot B} . IMPLEMENTATIONS AND gate
AND gate
using diodes AND gate
AND gate
using transistors NMOS AND gate
AND gate
An AND gate
AND gate
is usually designed using N-channel (pictured) or P-channel MOSFETs
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OR Gate
The OR GATE is a digital logic gate that implements logical disjunction – it behaves according to the truth table to the right. A HIGH output (1) results if one or both the inputs to the gate are HIGH (1). If neither input is high, a LOW output (0) results. In another sense, the function of OR effectively finds the maximum between two binary digits, just as the complementary AND function finds the minimum. CONTENTS * 1 Symbols * 2 Hardware description and pinout * 3 Implementations * 3.1 Alternatives * 4 Wired-OR * 5 See also * 6 References SYMBOLSThere are two symbols of OR gates: the American (ANSI or 'military') symbol and the IEC ('European' or 'rectangular') symbol, as well as the deprecated DIN
DIN
symbol. For more information see Logic Gate Symbols . MIL/ANSI Symbol IEC Symbol DIN
DIN
Symbol This schematic diagram shows the arrangement of four OR gates within a standard 4071 CMOS
CMOS
integrated circuit. HARDWARE DESCRIPTION AND PINOUTOR Gates are basic logic gates, and as such they are available in TTL and CMOS
CMOS
ICs logic families . The standard 4000 series CMOS
CMOS
IC is the 4071, which includes four independent two-input OR gates. The ancestral TTL device is the 7432
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XOR
but not is Venn diagram
Venn diagram
of A B C {displaystyle scriptstyle Aoplus Boplus C} {displaystyle ~oplus ~} {displaystyle ~Leftrightarrow ~} EXCLUSIVE OR or EXCLUSIVE DISJUNCTION is a logical operation that outputs true only when inputs differ (one is true, the other is false). It is symbolized by the prefix operator J and by the infix operators XOR (/ˌɛks ˈɔːr/ ), EOR, EXOR, ⊻, ⊕, ↮, and ≢. The negation of XOR is logical biconditional , which outputs true only when both inputs are the same. It gains the name "exclusive or" because the meaning of "or" is ambiguous when both operands are true; the exclusive or operator excludes that case. This is sometimes thought of as "one or the other but not both". This could be written as "A or B, but not, A and B". More generally, XOR is true only when an odd number of inputs are true. A chain of XORs—a XOR b XOR c XOR d (and so on)—is true whenever an odd number of the inputs are true and is false whenever an even number of inputs are true
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Xnor
The XNOR GATE (sometimes, EXNOR, ENOR, and, rarely, NXOR, XAND) is a digital logic gate whose function is the logical complement of the exclusive OR (XOR ) gate. The two-input version implements logical equality , behaving according to the truth table to the right. A high output (1) results if both of the inputs to the gate are the same. If one but not both inputs are high (1), a low output (0) results. The algebraic notation used to represent the XNOR operation is S = A B {displaystyle S=Aodot B} . CONTENTS * 1 Symbols * 2 Hardware description and pinout * 3 Alternatives * 4 See also * 5 References SYMBOLSThere are 2 symbols for XNOR gates : one with distinctive shape and one with rectangular shape and label. The distinctive symbol for the XN OR gate is that of the XOR gate with an added inversion bubble. Distinctive symbol Rectangular symbol The XN OR gate with inputs A and B implements the logical expression A B + A B {displaystyle Acdot B+{overline {A}}cdot {overline {B}}} . HARDWARE DESCRIPTION AND PINOUTXNOR gates are represented in most TTL and CMOS
CMOS
IC families. The standard 4000 series
4000 series
CMOS
CMOS
IC is the 4077 and the TTL IC is the 74266. Both include four independent, two-input, XNOR gates. The pinout diagram is as follows: Pinout diagram of a 74266 quad XNOR DIP -format IC
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Adder (electronics)
An ADDER is a digital circuit that performs addition of numbers. In many computers and other kinds of processors adders are used in the arithmetic logic units or ALU. They are also utilized in other parts of the processor, where they are used to calculate addresses , table indices, increment and decrement operators , and similar operations. Although adders can be constructed for many number representations , such as binary-coded decimal or excess-3 , the most common adders operate on binary numbers . In cases where two\'s complement or ones\' complement is being used to represent negative numbers , it is trivial to modify an adder into an adder–subtractor . Other signed number representations require more logic around the basic adder. CONTENTS* 1 Binary adders * 1.1 Half adder * 1.2 Full adder * 1.3 Adders supporting multiple bits * 1.3.1 Ripple-carry adder * 1.3.2 Carry-lookahead adder * 1.3.3 Carry-save adders * 1.4 3:2 compressors * 2 References * 3 See also * 4 External links BINARY ADDERSHALF ADDER Half adder logic diagram Half adder in action The HALF ADDER adds two single binary digits A and B. It has two outputs, sum (S) and carry (C). The carry signal represents an overflow into the next digit of a multi-digit addition. The value of the sum in decimal system is 2C + S. The simplest half-adder design, pictured on the right, incorporates an XOR gate for S and an AND gate for C
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Truth Table
A TRUTH TABLE is a mathematical table used in logic —specifically in connection with Boolean algebra , boolean functions , and propositional calculus —which sets out the functional values of logical expressions on each of their functional arguments, that is, for each combination of values taken by their logical variables (Enderton , 2001). In particular, truth tables can be used to show whethe