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Contour line
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This article is about lines of equal value in maps and diagrams. For more meanings of the word "contour", see Contour (disambiguation).
The bottom part of the diagram shows some contour lines with a straight line running through the location of the maximum value. The curve at the top represents the values along that straight line.
A three-dimensional surface, whose contour graph is below.
A two-dimensional contour graph of the three-dimensional surface in the above picture.
A contour line (also isocline, isopleth, isarithm, or equipotential curve) of a function of two variables is a curve along which the function has a constant value, so that the curve joins points of equal value.[1][2] It is a plane section of the three-dimensional graph of the function f(x, y) parallel to the x, y plane. In cartography, a contour line (often just called a "contour") joins points of equal elevation (height) above a given level, such as mean sea level.[3] A contour map is a map illustrated with contour lines, for example a topographic map, which thus shows valleys and hills, and the steepness or gentleness of slopes.[4] The contour interval of a contour map is the difference in elevation between successive contour lines.[5]
More generally, a contour line for a function of two variables is a curve connecting points where the function has the same particular value.[2]
The gradient of the function is always perpendicular to the contour lines. When the lines are close together the magnitude of the gradient is large: the variation is steep. A level set is a generalization of a contour line for functions of any number of variables.
Contour lines are curved, straight or a mixture of both lines on a map describing the intersection of a real or hypothetical surface with one or more horizontal planes. The configuration of these contours allows map readers to infer relative gradient of a parameter and estimate that parameter at specific places. Contour lines may be either traced on a visible three-dimensional model of the surface, as when a photogrammetrist viewing a stereo-model plots elevation contours, or interpolated from estimated surface elevations, as when a computer program threads contours through a network of observation points of area centroids. In the latter case, the method of interpolation affects the reliability of individual isolines and their portrayal of slope, pits and peaks.[6]
Contents
[hide]
1 Types
1.1 Equidistant points
1.2 Isopleths
1.3 Meteorology
1.3.1 Barometric pressure
1.3.2 Temperature and related subjects
1.3.3 Rainfall and air moisture
1.3.4 Wind
1.3.5 Freeze and thaw
1.4 Physical geography and oceanography
1.4.1 Elevation and depth
1.4.1.1 Interpretation
1.4.2 Electrostatics
1.4.3 Magnetism
1.4.4 Oceanography
1.5 Geology
1.6 Environmental science
1.7 Ecology
1.8 Social sciences
1.9 Statistics
1.10 Thermodynamics, engineering, and other sciences
1.11 Other phenomena
2 History
3 Graphical design
4 Plan view versus profile view
5 Labeling contour maps
6 See also
7 References
8 External links
Types[edit]
Contour lines are often given specific names beginning "iso-" (Ancient Greek: ἴσος, translit. isos, lit. 'equal') according to the nature of the variable being mapped, although in many usages the phrase "contour line" is most commonly used. Specific names are most common in meteorology, where multiple maps with different variables may be viewed simultaneously. The prefix "iso-" can be replaced with "isallo-" to specify a contour line connecting points where a variable changes at the same rate during a given time period.
The words isoline and isarithm (ἀριθμός arithmos "number") are general terms covering all types of contour line. The word isogram (γράμμα gramma "writing or drawing") was proposed by Francis Galton in 1889 as a convenient generic designation for lines indicating equality of some physical condition or quantity;[7] but it commonly refers to a word without a repeated letter.
An isogon (from γωνία or gonia, meaning 'angle') is a contour line for a variable which measures direction. In meteorology and in geomagnetics, the term isogon has specific meanings which are described below. An isocline (from κλίνειν or klinein, meaning 'to lean or slope') is a line joining points with equal slope. In population dynamics and in geomagnetics, the terms isocline and isoclinic line have specific meanings which are described below.
Equidistant points[edit]
A curve of equidistant points is a set of points all at the same distance from a given point, line, or polyline. In this case the function whose value is being held constant along a contour line is a distance function.
Isopleths[edit]
In geography, the word isopleth (from πλῆθος or plethos, meaning 'quantity') is used for contour lines that depict a variable which cannot be measured at a point, but which instead must be calculated from data collected over an area. An example is population density, which can be calculated by dividing the population of a census district by the surface area of that district. Each calculated value is presumed to be the value of the variable at the centre of the area, and isopleths can then be drawn by a process of interpolation. The idea of an isopleth map can be compared with that of a choropleth map.[8][9][10]
In meteorology, the word isopleth is used for any type of contour line.[11]
Meteorology[edit]
Isohyetal map of precipitation
Meteorological contour lines are based on interpolation of the point data received from weather stations and weather satellites. Weather stations are seldom exactly positioned at a contour line (when they are, this indicates a measurement precisely equal to the value of the contour). Instead, lines are drawn to best approximate the locations of exact values, based on the scattered information points available.
Meteorological contour maps may present collected data such as actual air pressure at a given time, or generalized data such as average pressure over a period of time, or forecast data such as predicted air pressure at some point in the future
Thermodynamic diagrams use multiple overlapping contour sets (including isobars and isotherms) to present a picture of the major thermodynamic factors in a weather system.
Barometric pressure[edit]
Loop showing the motion of a cold front by the movement of isallobars
An isobar (from βάρος or baros, meaning 'weight') is a line of equal or constant pressure on a graph, plot, or map; an isopleth or contour line of pressure. More accurately, isobars are lines drawn on a map joining places of equal average atmospheric pressure reduced to sea level for a specified period of time. In meteorology, the barometric pressures shown are reduced to sea level, not the surface pressures at the map locations.[12] The distribution of isobars is closely related to the magnitude and direction of the wind field, and can be used to predict future weather patterns. Isobars are commonly used in television weather reporting.
Isallobars are lines joining points of equal pressure change during a specific time interval.[13] These can be divided into anallobars, lines joining points of equal pressure increase during a specific time interval,[14] and katallobars, lines joining points of equal pressure decrease.[15] In general, weather systems move along an axis joining high and low isallobaric centers.[16] Isallobaric gradients are important components of the wind as they increase or decrease the geostrophic wind.
An isopycnal is a line of constant density. An isoheight or isohypse is a line of constant geopotential height on a constant pressure surface chart. Isohypse and isoheight are simply known as lines showing equal pressure on a map.
Temperature and related subjects[edit]
The 10 °C (50 °F) mean isotherm in July, marked by the red line, is commonly used to define the border of the Arctic region
An isotherm (from θέρμη or thermē, meaning 'heat') is a line that connects points on a map that have the same temperature. Therefore, all points through which an isotherm passes have the same or equal temperatures at the time indicated.[17][2] An isotherm at 0 °C is called the freezing level. The term was coined by the Prussian geographer and naturalist Alexander von Humboldt, who as part of his research into the geographical distribution of plants published the first map of isotherms in Paris, in 1817.[18]
An isogeotherm is a line of equal mean annual temperature. An isocheim is a line of equal mean winter temperature, and an isothere is a line of equal mean summer temperature.
An isohel (from ἥλιος or helios, meaning 'Sun') is a line of equal or constant solar radiation.
Rainfall and air moisture[edit]
An isohyet or isohyetal line (from ὕετος or huetos, meaning 'rain') is a line joining points of equal rainfall on a map in a given period . A map with isohyets is called an isohyetal map.
An isohume is a line of constant relative humidity, while a isodrosotherm (from δρόσος or drosos, meaning 'dew', and θέρμη or therme, meaning 'heat') is a line of equal or constant dew point.
An isoneph is a line indicating equal cloud cover.
An isochalaz is a line of constant frequency of hail storms, and an isobront is a line drawn through geographical points at which a given phase of thunderstorm activity occurred simultaneously.
Snow cover is frequently shown as a contour-line map.
Wind[edit]
An isotach (from ταχύς or tachus, meaning 'fast') is a line joining points with constant wind speed. In meteorology, the term isogon refers to a line of constant wind direction.
Freeze and thaw[edit]
An isopectic line denotes equal dates of ice formation each winter, and an isotac denotes equal dates of thawing.
Physical geography and oceanography[edit]
Elevation and depth[edit]
Topographic map of Stowe, Vermont. The brown contour lines represent the elevation. The contour interval is 20 feet.
Contours are one of several common methods used to denote elevation or altitude and depth on maps. From these contours, a sense of the general terrain can be determined. They are used at a variety of scales, from large-scale engineering drawings and architectural plans, through topographic maps and bathymetric charts, up to continental-scale maps.
"Contour line" is the most common usage in cartography, but isobath for underwater depths on bathymetric maps and isohypse for elevations are also used.
In cartography, the contour interval is the elevation difference between adjacent contour lines. The contour interval should be the same over a single map. When calculated as a ratio against the map scale, a sense of the hilliness of the terrain can be derived.
Interpretation[edit]
There are several rules to note when interpreting terrain contour lines:
The rule of Vs: sharp-pointed vees usually are in stream valleys, with the drainage channel passing through the point of the vee, with the vee pointing upstream. This is a consequence of erosion.
The rule of Os: closed loops are normally uphill on the inside and downhill on the outside, and the innermost loop is the highest area. If a loop instead represents a depression, some maps note this by short lines radiating from the inside of the loop, called "hachures".
Spacing of contours: close contours indicate a steep slope; distant contours a shallow slope. Two or more contour lines merging indicates a cliff. By counting the number of contours that cross a segment of a stream, the stream gradient can be approximated.
Of course, to determine differences in elevation between two points, the contour interval, or distance in altitude between two adjacent contour lines, must be known, and this is normally stated in the map key. Usually contour intervals are consistent throughout a map, but there are exceptions. Sometimes intermediate contours are present in flatter areas; these can be dashed or dotted lines at half the noted contour interval. When contours are used with hypsometric tints on a small-scale map that includes mountains and flatter low-lying areas, it is common to have smaller intervals at lower elevations so that detail is shown in all areas. Conversely, for an island which consists of a plateau surrounded by steep cliffs, it is possible to use smaller intervals as the height increases.[19]
Electrostatics[edit]
An isopotential map is a measure of electrostatic potential in space, often depicted in two dimensions with the electostatic charges inducing that electric potential. The term equipotential line or isopotential line refers to a curve of constant electric potential. Whether crossing an equipotential line represents ascending or descending the potential is inferred from the labels on the charges. In three dimensions, equipotential surfaces may be depicted with a two dimensional cross-section, showing equipotential lines at the intersection of the surfaces and the cross-section.
The general mathematical term level set is often used to describe the full collection of points having a particular potential, especially in higher dimensional space.
Magnetism[edit]
Isogonic lines for the year 2000. The agonic lines are thicker and labeled with "0".
In the study of the Earth's magnetic field, the term isogon or isogonic line refers to a line of constant magnetic declination, the variation of magnetic north from geographic north. An agonic line is drawn through points of zero magnetic declination. An isoporic line refers to a line of constant annual variation of magnetic declination .[20]
An isoclinic line connects points of equal magnetic dip, and an aclinic line is the isoclinic line of magnetic dip zero.
An isodynamic line (from δύναμις or dynamis meaning 'power') connects points with the same intensity of magnetic force.
Oceanography[edit]
Besides ocean depth, oceanographers use contour to describe diffuse variable phenomena much as meteorologists do with atmospheric phenomena. In particular, isobathytherms are lines showing depths of water with equal temperature, isohalines show lines of equal ocean salinity, and Isopycnals are surfaces of equal water density.
Geology[edit]
Various geological data are rendered as contour maps in structural geology, sedimentology, stratigraphy and economic geology. Contour maps are used to show the below ground surface of geologic strata, fault surfaces (especially low angle thrust faults) and unconformities. Isopach maps use isopachs (lines of equal thickness) to illustrate variations in thickness of geologic units.
Environmental science[edit]
In discussing pollution, density maps can be very useful in indicating sources and areas of greatest contamination. Contour maps are especially useful for diffuse forms or scales of pollution. Acid precipitation is indicated on maps with isoplats. Some of the most widespread applications of environmental science contour maps involve mapping of environmental noise (where lines of equal sound pressure level are denoted isobels[21]), air pollution, soil contamination, thermal pollution and groundwater contamination. By contour planting and contour ploughing, the rate of water runoff and thus soil erosion can be substantially reduced; this is especially important in riparian zones.
Ecology[edit]
An isoflor is an isopleth contour connecting areas of comparable biological diversity. Usually, the variable is the number of species of a given genus or family that occurs in a region. Isoflor maps are thus used to show distribution patterns and trends such as centres of diversity.[22]
Social sciences[edit]
From economics, an indifference map with three indifference curves shown. All points on a particular indifference curve have the same value of the utility function, whose values implicitly come out of the page in the unshown third dimension.
In economics, contour lines can be used to describe features which vary quantitatively over space. An isochrone shows lines of equivalent drive time or travel time to a given location and is used in the generation of isochrone maps. An isotim shows equivalent transport costs from the source of a raw material, and an isodapane shows equivalent cost of travel time.
A single production isoquant (convex) and a single isocost curve (linear). Labor usage is plotted horizontally and physical capital usage is plotted vertically.
Contour lines are also used to display non-geographic information in economics. Indifference curves (as shown at left) are used to show bundles of goods to which a person would assign equal utility. An isoquant (in the image at right) is a curve of equal production quantity for alternative combinations of input usages, and an isocost curve (also in the image at right) shows alternative usages having equal production costs.
In political science an analogous method is used in understanding coalitions (for example the diagram in Laver and Shepsle's work[23]).
In population dynamics, an isocline shows the set of population sizes at which the rate of change, or partial derivative, for one population in a pair of interacting populations is zero.
Statistics[edit]
In statistics, isodensity lines [24] or isodensanes are lines that join points with the same value of a probability density. Isodensanes are used to display bivariate distributions. For example, for a bivariate elliptical distribution the isodensity lines are ellipses.
Thermodynamics, engineering, and other sciences[edit]
Various types of graphs in thermodynamics, engineering, and other sciences use isobars (constant pressure), isotherms (constant temperature), isochors (constant specific volume), or other types of isolines, even though these graphs are usually not related to maps. Such isolines are useful for representing more than two dimensions (or quantities) on two-dimensional graphs. Common examples in thermodynamics are some types of phase diagrams.
Isoclines are used to solve ordinary differential equations.
In interpreting radar images, an isodop is a line of equal Doppler velocity, and an isoecho is a line of equal radar reflectivity.
Other phenomena[edit]
isochasm: aurora equal occurrence
isochor: volume
isodose: Absorbed dose of radiation
isophene: biological events occurring with coincidence such as plants flowering
isophote: illuminance
mobile telephony: mobile received power and cell coverage area
History[edit]
The idea of lines that join points of equal value was rediscovered several times. The oldest known isobath (contour line of constant depth) is found on a map dated 1584 of the river Spaarne, near Haarlem, by Dutchman Pieter Bruinsz.[25] In 1701, Edmond Halley used such lines (isogons) on a chart of magnetic variation.[26] The Dutch engineer Nicholas Cruquius drew the bed of the river Merwede with lines of equal depth (isobaths) at intervals of 1 fathom in 1727, and Philippe Buache used them at 10-fathom intervals on a chart of the English Channel that was prepared in 1737 and published in 1752. Such lines were used to describe a land surface (contour lines) in a map of the Duchy of Modena and Reggio by Domenico Vandelli in 1746, and they were studied theoretically by Ducarla in 1771, and Charles Hutton used them in the Schiehallion experiment. In 1791, a map of France by J. L. Dupain-Triel used contour lines at 20-metre intervals, hachures, spot-heights and a vertical section. In 1801, the chief of the Corps of Engineers, Haxo, used contour lines at the larger scale of 1:500 on a plan of his projects for Rocca d'Aufo.[27][28][29]
By around 1843, when the Ordnance Survey started to regularly record contour lines in Great Britain and Ireland, they were already in general use in European countries. Isobaths were not routinely used on nautical charts until those of Russia from 1834, and those of Britain from 1838.[27][30][31]
When maps with contour lines became common, the idea spread to other applications. Perhaps the latest to develop are air quality and noise pollution contour maps, which first appeared in the United States in approximately 1970, largely as a result of national legislation requiring spatial delineation of these parameters. In 2007, Pictometry International was the first to allow users to dynamically generate elevation contour lines to be laid over oblique images.
Graphical design[edit]
For features specific to topography, see Terrain cartography § Contour lines, and Topographic map § Conventions.
To maximize readability of contour maps, there are several design choices available to the map creator, principally line weight, line color, line type and method of numerical marking.
Line weight is simply the darkness or thickness of the line used. This choice is made based upon the least intrusive form of contours that enable the reader to decipher the background information in the map itself. If there is little or no content on the base map, the contour lines may be drawn with relatively heavy thickness. Also, for many forms of contours such as topographic maps, it is common to vary the line weight and/or color, so that a different line characteristic occurs for certain numerical values. For example, in the topographic map above, the even hundred foot elevations are shown in a different weight from the twenty foot intervals.
Line color is the choice of any number of pigments that suit the display. Sometimes a sheen or gloss is used as well as color to set the contour lines apart from the base map. Line colour can be varied to show other information.
Line type refers to whether the basic contour line is solid, dashed, dotted or broken in some other pattern to create the desired effect. Dotted or dashed lines are often used when the underlying base map conveys very important (or difficult to read) information. Broken line types are used when the location of the contour line is inferred.
Numerical marking is the manner of denoting the arithmetical values of contour lines. This can be done by placing numbers along some of the contour lines, typically using interpolation for intervening lines. Alternatively a map key can be produced associating the contours with their values.
If the contour lines are not numerically labeled and adjacent lines have the same style (with the same weight, color and type), then the direction of the gradient cannot be determined from the contour lines alone. However, if the contour lines cycle through three or more styles, then the direction of the gradient can be determined from the lines. The orientation of the numerical text labels is often used to indicate the direction of the slope.
Plan view versus profile view[edit]
See also: Topographic profile
Most commonly contour lines are drawn in plan view, or as an observer in space would view the Earth's surface: ordinary map form. However, some parameters can often be displayed in profile view showing a vertical profile of the parameter mapped. Some of the most common parameters mapped in profile are air pollutant concentrations and sound levels. In each of those cases it may be important to analyze (air pollutant concentrations or sound levels) at varying heights so as to determine the air quality or noise health effects on people at different elevations, for example, living on different floor levels of an urban apartment. In actuality, both plan and profile view contour maps are used in air pollution and noise pollution studies.
Labeling contour maps[edit]
Contour map labeled aesthetically in an "elevation up" manner.
Labels are a critical component of elevation maps. A properly labeled contour map helps the reader to quickly interpret the shape of the terrain. If numbers are placed close to each other, it means that the terrain is steep. Labels should be placed along a slightly curved line "pointing" to the summit or nadir, from several directions if possible, making the visual identification of the summit or nadir easy.[32][33] Contour labels can be oriented so a reader is facing uphill when reading the label.
Manual labeling of contour maps is a time-consuming process, however, there are a few software systems that can do the job automatically and in accordance with cartographic conventions, called automatic label placement.
See also[edit]
Atlas portal
Aeronautical chart
Cartogram
Compass rose
Dymaxion map
Estate map
Fall line (topography)
Fantasy map
Floor plan
Geologic map
Map design
Marching squares
Nautical chart
Pictorial maps
Planform
Plat
Reversed map
Road atlas
Street map
TERCOM
Thematic map
Topographic map
World map
References[edit]
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Geography of Chicago
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Geography of Chicago and surrounding counties.
The city of Chicago is located in northern Illinois, United States, at the south western tip of Lake Michigan. It sits on the Saint Lawrence Seaway continental divide at the site of the Chicago Portage, an ancient trade route connecting the Mississippi River and the Great Lakes watersheds.
Contents
[hide]
1 Geography
1.1 Climate
2 Statistics
3 Cityscape
4 See also
5 Notes
6 References
Geography[edit]
Chicago's present natural geography is a result of the large glaciers of the Ice Age, namely the Wisconsinan Glaciation that carved out the modern basin of Lake Michigan (which formed from the glacier's meltwater). The city of Chicago itself sits on the Chicago Plain, a flat plain that was once the bottom of ancestral Lake Chicago. This plain has very little topographical relief, in fact, topographical relief is so unusual in the plain that what would be unnoticed hills and ridges in other locales have been given names. The highest natural point within the city limits is in the Beverly neighborhood at 41°42′12.5″N 87°40′37″W / 41.703472°N 87.67694°W / 41.703472; -87.67694 at 672 ft (205 m).[1] In pioneer days, this hill was called Blue Island, so named because at a distance it looked like an island set in a trackless prairie sea. In fact it, and the nearby Stony Island, were both islands in Lake Chicago, as it receded. On the North side, the diagonals Clark Street and Ridge Boulevard run along ridges that were once sandbars in the Lake.
One special feature of the Chicago area was the now-vanished Mud Lake in the Des Plaines River watershed. During heavy periods of rain or when the Des Plaines overflowed its banks due to downstream ice dams in the early spring, the river would flow through Mud Lake to the South Branch of the Chicago River, forming a favorite portage for early traders and creating the path of the future I&M and Chicago Sanitary and Ship Canals. When the city we know today was initially founded in the 1830s, the land was swampy and most of the early building began on low dunes around the Chicago River's mouth. Indeed, Chicago's low lying geography, which ultimately became crucial to its boom town development (as the site of the Chicago Portage and canal), could not initially attract substantial early settlement because the tall grass prairie around its lake and river systems was underlain by hard packed glacial clay, making much of the area forbidding wetlands.[2] Thus, the paradox of Chicago's development as a city in the 19th century became taking advantage of this geography, but also overcoming its limitations.
North of the city of Chicago, there are steep bluffs and ravines that run along Lake Michigan. In contrast, south of the city of Chicago into Northwest Indiana it is without bluffs, but instead has sand dunes. The greatest example of these can be seen at Indiana Dunes National Lakeshore, where some dunes reach up to almost 200 feet. Farther inland, a series of moraines surrounds the Chicago Plain. This surrounding area is hilly and higher than the Chicago Plain. Past the moraines, the land flattens out again, but is interspersed with a few deep river valleys such as the Illinois River, Fox River, Des Plaines River, and Kankakee River. Here you may find rock cliffs and rock ravines, which are absent from the interior Chicago area (the ravines of the north shore and south suburbs are soil ravines without any rock).
City limits of Chicago.
Also, a very large limestone quarry (Thornton Quarry) exists just south of the city of Chicago in the suburb of Thornton. It was once a coral reef when the Midwest was covered by a warm inland sea (hundreds of millions of years before the glaciation of the Chicago area). The rest of the Chicago area does not have bedrock this close to the surface.
Climate[edit]
Main article: Climate of Chicago
The city lies within the humid continental climate zone, and experiences four distinct seasons. Summers are warm and humid with a July average of 75.5 °F (24.2 °C). Winters are cold, snowy and windy with temperatures below freezing. Spring and fall are mild with moderate humidity. According to the National Weather Service, Chicago’s highest official temperature reading of 107 °F (42 °C) was recorded on June 1, 1934. The lowest temperature of −27 °F (−33 °C) was recorded on January 20, 1985. Along with long, hot dry spells in the summer, Chicago can suffer extreme winter cold spells. In the entire month of January 1977, the temperature did not rise above 31 °F (−0.6 °C). The average temperature that month was around 10 °F (−12 °C).
Chicago’s yearly precipitation averages about 34 inches (860 millimeters). Summer is typically the rainiest season, with short-lived rainfall and thunderstorms more common than prolonged rainy periods.[3] Winter precipitation tends to be more snow than rain. Chicago's snowiest winter on record was that of 1978–79, with 89.7 inches (227.8 cm) of snow in total. The winter of 2007-08, with more than 61 inches (155 cm) of snow, was the snowiest in nearly three decades, and the winter of 2008/2009 produced just over 50 inches (127 cm). This marked the first time in three decades that back-to-back winters produced 50 inches or more of snow. Average winter snowfall is normally, depending on the reporting location, 43.1 inches (109.5 cm). The highest one-day snowfall total in Chicago history was 18.6 inches (47.2 cm) on January 2, 1999.[4] Chicago’s highest one-day rainfall total was 6.63 inches (168.4 mm) on September 13, 2008.[5] The previous record of 6.49 inches (164.8 mm) had been set on August 14, 1987. The record for yearly rainfall is 50.86 inches (1,292 mm) set in 2008; 1983 was the wettest year before with 49.35 inches (1,253 mm).[5]

[show]Climate data for Chicago (Midway Airport), 1981–2010 normals,[a] extremes 1928–present
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year
Record high °F (°C)
67
(19) 75
(24) 86
(30) 92
(33) 102
(39) 107
(42) 109
(43) 102
(39) 101
(38) 94
(34) 81
(27) 72
(22) 109
(43)
Mean maximum °F (°C)
52.3
(11.3) 57.2
(14) 73.0
(22.8) 82.2
(27.9) 88.2
(31.2) 94.1
(34.5) 96.5
(35.8) 94.1
(34.5) 90.5
(32.5) 82.2
(27.9) 68.7
(20.4) 55.7
(13.2) 97.7
(36.5)
Average high °F (°C)
31.5
(−0.3) 35.8
(2.1) 46.8
(8.2) 59.2
(15.1) 70.2
(21.2) 79.9
(26.6) 84.2
(29) 82.1
(27.8) 75.3
(24.1) 62.8
(17.1) 48.6
(9.2) 35.3
(1.8) 59.4
(15.2)
Daily mean °F (°C)
24.8
(−4) 28.7
(−1.8) 38.8
(3.8) 50.4
(10.2) 60.9
(16.1) 71.0
(21.7) 75.9
(24.4) 74.1
(23.4) 66.4
(19.1) 54.2
(12.3) 41.5
(5.3) 29.0
(−1.7) 51.4
(10.8)
Average low °F (°C)
18.2
(−7.7) 21.7
(−5.7) 30.9
(−0.6) 41.7
(5.4) 51.6
(10.9) 62.1
(16.7) 67.5
(19.7) 66.2
(19) 57.5
(14.2) 45.7
(7.6) 34.5
(1.4) 22.7
(−5.2) 43.5
(6.4)
Mean minimum °F (°C)
−3.3
(−19.6) 2.4
(−16.4) 14.3
(−9.8) 27.0
(−2.8) 38.4
(3.6) 48.6
(9.2) 56.8
(13.8) 56.1
(13.4) 43.1
(6.2) 31.1
(−0.5) 19.9
(−6.7) 2.2
(−16.6) −8.7
(−22.6)
Record low °F (°C)
−25
(−32) −20
(−29) −7
(−22) 10
(−12) 28
(−2) 35
(2) 46
(8) 43
(6) 34
(1) 20
(−7) −3
(−19) −20
(−29) −25
(−32)
Average precipitation inches (mm)
2.06
(52.3) 1.94
(49.3) 2.72
(69.1) 3.64
(92.5) 4.13
(104.9) 4.06
(103.1) 4.01
(101.9) 3.99
(101.3) 3.31
(84.1) 3.24
(82.3) 3.42
(86.9) 2.57
(65.3) 39.09
(992.9)
Average snowfall inches (cm)
11.5
(29.2) 9.1
(23.1) 5.4
(13.7) 1.0
(2.5) trace 0
(0) 0
(0) 0
(0) 0
(0) 0.1
(0.3) 1.3
(3.3) 8.7
(22.1) 37.1
(94.2)
Average precipitation days (≥ 0.01 in)
10.7 8.8 11.2 11.1 11.4 10.3 9.9 9.0 8.2 10.2 11.2 11.1 123.1
Average snowy days (≥ 0.1 in)
8.1 5.5 3.8 0.7 0 0 0 0 0 0.1 1.8 6.7 26.7
Source: NOAA,[6][7][8] WRCC[9]
[show]Climate data for Chicago (O'Hare Int'l Airport), 1981–2010 normals,[a] extremes 1871–present[b]
Month
Jan
Feb
Mar
Apr
May
Jun
Jul
Aug
Sep
Oct
Nov
Dec
Year
Record high °F (°C)
67
(19) 75
(24) 88
(31) 91
(33) 98
(37) 104
(40) 105
(41) 102
(39) 101
(38) 94
(34) 81
(27) 71
(22) 105
(41)
Mean maximum °F (°C)
51.4
(10.8) 56.5
(13.6) 72.4
(22.4) 81.7
(27.6) 87.2
(30.7) 93.6
(34.2) 95.5
(35.3) 93.4
(34.1) 89.7
(32.1) 81.1
(27.3) 67.6
(19.8) 55.0
(12.8) 96.8
(36)
Average high °F (°C)
31.0
(−0.6) 35.3
(1.8) 46.6
(8.1) 59.0
(15) 70.0
(21.1) 79.7
(26.5) 84.1
(28.9) 81.9
(27.7) 74.8
(23.8) 62.3
(16.8) 48.2
(9) 34.8
(1.6) 59.1
(15.1)
Daily mean °F (°C)
23.8
(−4.6) 27.7
(−2.4) 37.9
(3.3) 48.9
(9.4) 59.1
(15.1) 68.9
(20.5) 74.0
(23.3) 72.4
(22.4) 64.6
(18.1) 52.5
(11.4) 40.3
(4.6) 27.7
(−2.4) 49.9
(9.9)
Average low °F (°C)
16.5
(−8.6) 20.1
(−6.6) 29.2
(−1.6) 38.8
(3.8) 48.3
(9.1) 58.1
(14.5) 63.9
(17.7) 62.9
(17.2) 54.3
(12.4) 42.8
(6) 32.4
(0.2) 20.7
(−6.3) 40.8
(4.9)
Mean minimum °F (°C)
−5.6
(−20.9) −0.3
(−17.9) 11.9
(−11.2) 23.5
(−4.7) 35.6
(2) 44.3
(6.8) 52.0
(11.1) 52.6
(11.4) 39.2
(4) 28.4
(−2) 16.9
(−8.4) −0.1
(−17.8) −10.9
(−23.8)
Record low °F (°C)
−27
(−33) −21
(−29) −12
(−24) 7
(−14) 27
(−3) 35
(2) 45
(7) 42
(6) 29
(−2) 14
(−10) −2
(−19) −25
(−32) −27
(−33)
Average precipitation inches (mm)
1.73
(43.9) 1.79
(45.5) 2.50
(63.5) 3.38
(85.9) 3.68
(93.5) 3.45
(87.6) 3.70
(94) 4.90
(124.5) 3.21
(81.5) 3.15
(80) 3.15
(80) 2.25
(57.2) 36.89
(937)
Average snowfall inches (cm)
10.8
(27.4) 9.1
(23.1) 5.6
(14.2) 1.2
(3) trace 0
(0) 0
(0) 0
(0) 0
(0) 0.2
(0.5) 1.2
(3) 8.2
(20.8) 36.3
(92.2)
Average precipitation days (≥ 0.01 in)
10.5 8.8 11.1 12.0 11.6 10.2 9.8 9.8 8.3 10.2 10.8 11.0 124.1
Average snowy days (≥ 0.1 in)
8.2 5.9 4.2 0.9 0 0 0 0 0 0.2 1.7 6.9 28.0
Average relative humidity (%)
72.2 71.6 69.7 64.9 64.1 65.6 68.5 70.7 71.1 68.6 72.5 75.5 69.6
Mean monthly sunshine hours
135.8 136.2 187.0 215.3 281.9 311.4 318.4 283.0 226.6 193.2 113.3 106.3 2,508.4
Percent possible sunshine
46 46 51 54 62 68 69 66 60 56 38 37 56
Source: NOAA (relative humidity and sun 1961–1990)[7][12][13]
Statistics[edit]
According to the United States Census Bureau, the City of Chicago has a total area of 606.1 km² (234.0 mi²). 588.3 km² (227.1 mi²) of it is land and 17.8 square kilometres (6.9 sq mi) of it is water. The total area is 2.94% water. The city has been built on relatively flat land, the average height of land is 579 feet (176 m) above sea level. The centroid (geographical center) of the city is at 41°50′26″N 87°40′46″W / 41.840675°N 87.679365°W / 41.840675; -87.679365,[14] southeast of 28th and Leavitt Streets in an industrial area near the Chicago Sanitary and Ship Canal. (Before annexations in the 1950s, notably for O'Hare International Airport, references placed the geographical center near 37th and Honore Streets.) Chicago, along with New York City and Los Angeles, California are the three most populous cities of the U.S., yet Chicago is only half the other two cities' individual land areas. Chicago's nickname, "The Windy City," actually acquired from a political op-ed piece, fits the city well as its location on Lake Michigan moderates the climate and often provides a breeze.
The Chicago Metropolitan Statistical Area (MSA) consists of Cook county and five surrounding Illinois counties as well as the Chicago–Gary–Kenosha Combined Statistical Area (CSA) which is made up of nine counties, two of them in northwestern Indiana and one in southeastern Wisconsin.
The Chicago skyline.
Cityscape[edit]
This article possibly contains original research. Please improve it by verifying the claims made and adding inline citations. Statements consisting only of original research should be removed. (April 2008) (Learn how and when to remove this template message)
After building the first ever skyscraper (Home Insurance Building), Chicago has been at the forefront of skyscraper building ever since. Today Chicago can boast to having 4 of the 10 tallest buildings in the United States and 9 of the 100 in the world.
By modern standards, Chicago has little reason to build up: being located in the Midwest, it has plenty of room to sprawl outwards on almost Euclideanesque flat ground. There is the Chicago River, which may bring some argument as to geographic restriction, but the impact of which was strongly lessened by the strict adherence to the Chicago grid across the river.
Today, Chicago is going through a massive skyscraper building boom, with projects like 55 East Erie (the tallest residential building in the U.S. outside New York City) and Trump International Hotel (completed in August 2008, it is the second tallest in Chicago and the tallest building built in the U.S. for nearly three decades) breaking ground frequently. This can be attributed to the precedent that Chicago has always had a history of frantic skyscraper building, mostly beginning after the Great Chicago Fire when the price of land in the city increased. This caused architects to start building upward. Since this time developers simply follow the pattern set before them.
See also[edit]
Chicago River
Chicago Sanitary and Ship Canal
I&M Canal
Lake Michigan
Notes[edit]
^ Jump up to: a b Mean monthly maxima and minima (i.e. the expected highest and lowest temperature readings at any point during the year or given month) calculated based on data at said location from 1981 to 2010.
Jump up ^ Official records for Chicago were kept at various locations in downtown from January 1871 to 31 December 1925, University of Chicago from 1 January 1926 to 30 June 1942, Midway Airport from 1 July 1942 to 16 January 1980, and at O'Hare Airport since 17 January 1980.[10][11]
References[edit]
Jump up ^ "Chicago Facts" (PDF). Northeastern Illinois University. p. 46. Archived from the original (PDF) on 10 November 2013. Retrieved 28 August 2013.
Jump up ^ Donald L. Miller, City of the Century, p. 67 (Simon & Schuster, New York, 1996)
Jump up ^ Chicago Seasonal Temperature and Precipitation Rankings (11/25/2005). National Weather Service Weather Forecast Office - Chicago, IL.
Jump up ^ "January Weather Trivia". National Weather Service. Retrieved 2012-03-21.
^ Jump up to: a b [1]. National Weather Service Weather Forecast Office - Chicago, IL.
Jump up ^ "Station Name: IL CHICAGO MIDWAY AP". National Climatic Data Center. Retrieved 2013-03-12.
^ Jump up to: a b "NowData - NOAA Online Weather Data". NWS Romeoville, IL. Retrieved 2016-04-18.
Jump up ^ "Top 20 Weather Events of the Century for Chicago and Northeast Illinois 1900–1999". NWS Romeoville, IL. Retrieved 2014-06-16.
Jump up ^ "CHICAGO MIDWAY AP 3 SW, ILLINOIS". Western Regional Climate Center. Retrieved 2014-06-12.
Jump up ^ History of the Chicago and Rockford weather observation sites
Jump up ^ ThreadEx
Jump up ^ "Station Name: IL CHICAGO OHARE INTL AP". National Oceanic and Atmospheric Administration. Retrieved 2013-03-18.
Jump up ^ "Chicago/O'Hare, IL Climate Normals 1961-1990". National Oceanic and Atmospheric Administration. Retrieved May 14, 2013.
Jump up ^ "Geographic Midpoint Calculator". GeoMidpoint.com. Retrieved 25 October 2013.
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Field-effect transistor
From Wikipedia, the free encyclopedia
Jump to: navigation, search
"FET" redirects here. For other uses, see FET (disambiguation).
The field-effect transistor (FET) is a transistor that uses an electric field to control the electrical behaviour of the device. FETs are also known as unipolar transistors since they involve single-carrier-type operation. Many different implementations of field effect transistors exist. Field effect transistors generally display very high input impedance at low frequencies. The conductivity between the drain and source terminals is controlled by an electric field in the device, which is generated by the voltage difference between the body and the gate of the device.
Contents
[hide]
1 History
2 Basic information
3 More about terminals
3.1 Effect of gate voltage on current
3.1.1 n-channel
3.1.2 p-channel
3.2 Effect of source/drain voltage on channel
4 Composition
5 Types
6 Advantages
7 Disadvantages
8 Uses
9 Source-gated transistor
10 See also
11 References
12 External links
History[edit]
Main article: History of the transistor
The field-effect transistor was first patented by Julius Edgar Lilienfeld in 1926 and by Oskar Heil in 1934, but practical semiconducting devices (the junction field-effect transistors [JFETs]) were developed later after the transistor effect was observed and explained by the team of William Shockley at Bell Labs in 1947, immediately after the 20-year patent period eventually expired.
The first type of JFET was the static induction transistor (SIT), invented by Japanese engineers Jun-ichi Nishizawa and Y. Watanabe in 1950. The SIT is a type of JFET with a short channel length.[1] The metal–oxide–semiconductor field-effect transistor (MOSFET), which largely superseded the JFET and had a profound effect on digital electronic development, was invented by Dawon Kahng and Martin Atalla in 1959.[2]
Basic information[edit]
See also: Charge carrier § Majority and minority carriers
FETs can be majority-charge-carrier devices, in which the current is carried predominantly by majority carriers, or minority-charge-carrier devices, in which the current is mainly due to a flow of minority carriers.[3] The device consists of an active channel through which charge carriers, electrons or holes, flow from the source to the drain. Source and drain terminal conductors are connected to the semiconductor through ohmic contacts. The conductivity of the channel is a function of the potential applied across the gate and source terminals.
The FET's three terminals are:[4]
source (S), through which the carriers enter the channel. Conventionally, current entering the channel at S is designated by IS.
drain (D), through which the carriers leave the channel. Conventionally, current entering the channel at D is designated by ID. Drain-to-source voltage is VDS.
gate (G), the terminal that modulates the channel conductivity. By applying voltage to G, one can control ID.
More about terminals[edit]
Cross section of an n-type MOSFET
All FETs have source, drain, and gate terminals that correspond roughly to the collector, emitter, and base of BJTs. Most FETs have a fourth terminal called the body, base, bulk, or substrate. This fourth terminal serves to bias the transistor into operation; it is rare to make non-trivial use of the body terminal in circuit designs, but its presence is important when setting up the physical layout of an integrated circuit. The size of the gate, length L in the diagram, is the distance between source and drain. The width is the extension of the transistor, in the direction perpendicular to the cross section in the diagram (i.e., into/out of the screen). Typically the width is much larger than the length of the gate. A gate length of 1 µm limits the upper frequency to about 5 GHz, 0.2 µm to about 30 GHz.
The names of the terminals refer to their functions. The gate terminal may be thought of as controlling the opening and closing of a physical gate. This gate permits electrons to flow through or blocks their passage by creating or eliminating a channel between the source and drain. Electron-flow from the source terminal towards the drain terminal is influenced by an applied voltage. The body simply refers to the bulk of the semiconductor in which the gate, source and drain lie. Usually the body terminal is connected to the highest or lowest voltage within the circuit, depending on the type of the FET. The body terminal and the source terminal are sometimes connected together since the source is often connected to the highest or lowest voltage within the circuit, although there are several uses of FETs which do not have such a configuration, such as transmission gates and cascode circuits.
Effect of gate voltage on current[edit]
I–V characteristics and output plot of a JFET n-channel transistor.
Simulation result for right side: formation of inversion channel (electron density) and left side: current-gate voltage curve(transfer characteristics) in an n-channel nanowire MOSFET. Note that the threshold voltage for this device lies around 0.45 V.
FET conventional symbol types
The FET controls the flow of electrons (or electron holes) from the source to drain by affecting the size and shape of a 'conductive channel' created and influenced by voltage (or lack of voltage) applied across the gate and source terminals. (For simplicity, this discussion assumes that the body and source are connected.) This conductive channel is the "stream" through which electrons flow from source to drain.
n-channel[edit]
In an n-channel 'depletion-mode' device, a negative gate-to-source voltage causes a depletion region to expand in width and encroach on the channel from the sides, narrowing the channel. If the active region expands to completely close the channel, the resistance of the channel from source to drain becomes large, and the FET is effectively turned off like a switch (see right figure, when there is very small current). This is called 'pinch-off', and the voltage at which it occurs is called the 'pinch-off voltage'. Conversely, a positive gate-to-source voltage increases the channel size and allows electrons to flow easily (see right figure, when there is a conduction channel and current is large).
In an n-channel 'enhancement-mode' device, a conductive channel does not exist naturally within the transistor, and a positive gate-to-source voltage is necessary to create one. The positive voltage attracts free-floating electrons within the body towards the gate, forming a conductive channel. But first, enough electrons must be attracted near the gate to counter the dopant ions added to the body of the FET; this forms a region with no mobile carriers called a depletion region, and the voltage at which this occurs is referred to as the threshold voltage of the FET. Further gate-to-source voltage increase will attract even more electrons towards the gate which are able to create a conductive channel from source to drain; this process is called inversion.
p-channel[edit]
In a p-channel 'depletion-mode' device, a positive voltage from gate to body creates a depletion layer by forcing the positively charged holes to the gate-insulator/semiconductor interface, leaving exposed a carrier-free region of immobile, negatively charged acceptor ions. Conversely, in a p-channel 'enhancement-mode' device, a conductive region does not exist and negative voltage must be used to generate a conduction channel.
Effect of source/drain voltage on channel[edit]
For either enhancement- or depletion-mode devices, at drain-to-source voltages much less than gate-to-source voltages, changing the gate voltage will alter the channel resistance, and drain current will be proportional to drain voltage (referenced to source voltage). In this mode the FET operates like a variable resistor and the FET is said to be operating in a linear mode or ohmic mode.[5][6]
If drain-to-source voltage is increased, this creates a significant asymmetrical change in the shape of the channel due to a gradient of voltage potential from source to drain. The shape of the inversion region becomes "pinched-off" near the drain end of the channel. If drain-to-source voltage is increased further, the pinch-off point of the channel begins to move away from the drain towards the source. The FET is said to be in saturation mode;[7] although some authors refer to it as active mode, for a better analogy with bipolar transistor operating regions.[8][9] The saturation mode, or the region between ohmic and saturation, is used when amplification is needed. The in-between region is sometimes considered to be part of the ohmic or linear region, even where drain current is not approximately linear with drain voltage.
Even though the conductive channel formed by gate-to-source voltage no longer connects source to drain during saturation mode, carriers are not blocked from flowing. Considering again an n-channel enhancement-mode device, a depletion region exists in the p-type body, surrounding the conductive channel and drain and source regions. The electrons which comprise the channel are free to move out of the channel through the depletion region if attracted to the drain by drain-to-source voltage. The depletion region is free of carriers and has a resistance similar to silicon. Any increase of the drain-to-source voltage will increase the distance from drain to the pinch-off point, increasing the resistance of the depletion region in proportion to the drain-to-source voltage applied. This proportional change causes the drain-to-source current to remain relatively fixed, independent of changes to the drain-to-source voltage, quite unlike its ohmic behavior in the linear mode of operation. Thus, in saturation mode, the FET behaves as a constant-current source rather than as a resistor, and can effectively be used as a voltage amplifier. In this case, the gate-to-source voltage determines the level of constant current through the channel.
Composition[edit]
FETs can be constructed from various semiconductors, with silicon being by far the most common. Most FETs are made by using conventional bulk semiconductor processing techniques, using a single crystal semiconductor wafer as the active region, or channel.
Among the more unusual body materials are amorphous silicon, polycrystalline silicon or other amorphous semiconductors in thin-film transistors or organic field-effect transistors (OFETs) that are based on organic semiconductors; often, OFET gate insulators and electrodes are made of organic materials, as well. Such FETs are manufactured using a variety of materials such as silicon carbide (SiC), gallium arsenide (GaAs), gallium nitride (GaN), and indium gallium arsenide (InGaAs).
In June 2011, IBM announced that it had successfully used graphene-based FETs in an integrated circuit.[10][11] These transistors are capable of about 2.23 GHz cutoff frequency, much higher than standard silicon FETs.[12]
Types[edit]
Depletion-type FETs under typical voltages: JFET, poly-silicon MOSFET, double-gate MOSFET, metal-gate MOSFET, MESFET.
Depletion
Electrons
Holes
Metal
Insulator
Top: source, bottom: drain, left: gate, right: bulk. Voltages that lead to channel formation are not shown.
The channel of a FET is doped to produce either an n-type semiconductor or a p-type semiconductor. The drain and source may be doped of opposite type to the channel, in the case of enhancement mode FETs, or doped of similar type to the channel as in depletion mode FETs. Field-effect transistors are also distinguished by the method of insulation between channel and gate. Types of FETs include:
The JFET (junction field-effect transistor) uses a reverse biased p–n junction to separate the gate from the body.
The MOSFET (metal–oxide–semiconductor field-effect transistor) utilizes an insulator (typically SiO2) between the gate and the body.
The MNOS Metal-Nitride-Oxide-Semiconductor transistor utilizes an nitride-oxide layer insulator between the gate and the body.
The DGMOSFET (Dual-gate MOSFET), a FET with two insulated gates.
The DEPFET is a FET formed in a fully depleted substrate and acts as a sensor, amplifier and memory node at the same time. It can be used as an image (photon) sensor.
The FREDFET (fast-reverse or fast-recovery epitaxial diode FET) is a specialized FET designed to provide a very fast recovery (turn-off) of the body diode.
The HIGFET (heterostructure insulated gate field-effect transistor) is now used mainly in research.[13]
The MODFET (modulation-doped field-effect transistor) is a high-electron-mobility transistor using a quantum well structure formed by graded doping of the active region.
The TFET (tunnel field-effect transistor) is based on band-to-band tunneling.[14]
The IGBT (insulated-gate bipolar transistor) is a device for power control. It has a structure akin to a MOSFET coupled with a bipolar-like main conduction channel. These are commonly used for the 200–3000 V drain-to-source voltage range of operation. Power MOSFETs are still the device of choice for drain-to-source voltages of 1 to 200 V.
The HEMT (high-electron-mobility transistor), also called a HFET (heterostructure FET), can be made using bandgap engineering in a ternary semiconductor such as AlGaAs. The fully depleted wide-band-gap material forms the isolation between gate and body.
The ISFET (ion-sensitive field-effect transistor) can be used to measure ion concentrations in a solution; when the ion concentration (such as H+, see pH electrode) changes, the current through the transistor will change accordingly.
The BioFET (Biologically sensitive field-effect transistor) is a class of sensors/biosensors based on ISFET technology which are utilized to detect charged molecules; when a charged molecule is present, changes in the electrostatic field at the BioFET surface result in a measurable change in current through the transistor. These include EnFETs, ImmunoFETs, GenFETs, DNAFETs, CPFETs, BeetleFETs, and FETs based on ion-channels/protein binding.[15]
The MESFET (metal–semiconductor field-effect transistor) substitutes the p–n junction of the JFET with a Schottky barrier; and is used in GaAs and other III-V semiconductor materials.
The NOMFET is a nanoparticle organic memory field-effect transistor.[16]
The GNRFET (graphene nanoribbon field-effect transistor) uses a graphene nanoribbon for its channel.[17]
The VeSFET (vertical-slit field-effect transistor) is a square-shaped junctionless FET with a narrow slit connecting the source and drain at opposite corners. Two gates occupy the other corners, and control the current through the slit.[18]
The CNTFET (carbon nanotube field-effect transistor).
The OFET (organic field-effect transistor) uses an organic semiconductor in its channel.
The DNAFET (DNA field-effect transistor) is a specialized FET that acts as a biosensor, by using a gate made of single-strand DNA molecules to detect matching DNA strands.
The QFET (quantum field effect transistor) takes advantage of quantum tunneling to greatly increase the speed of transistor operation by eliminating the traditional transistor's area of electron conduction.
Advantages[edit]
One advantage of the FET is its high gate to main current resistance, on the order of 100 MΩ or more, thus providing a high degree of isolation between control and flow. Because base current noise will increase with shaping time,[19] a FET typically produces less noise than a bipolar junction transistor (BJT), and is thus found in noise sensitive electronics such as tuners and low-noise amplifiers for VHF and satellite receivers. It is relatively immune to radiation. It exhibits no offset voltage at zero drain current and hence makes an excellent signal chopper. It typically has better thermal stability than a BJT.[4] Because they are controlled by gate charge, once the gate is closed or opened, there is no additional power draw, as there would be with a bipolar junction transistor or with non-latching relays in some states. This allows extremely low-power switching, which in turn allows greater miniaturization of circuits because heat dissipation needs are reduced compared to other types of switches.
Disadvantages[edit]
It has a relatively low gain–bandwidth product compared to a BJT. The MOSFET has a drawback of being very susceptible to overload voltages, thus requiring special handling during installation.[20] The fragile insulating layer of the MOSFET between the gate and channel makes it vulnerable to electrostatic discharge or changes to threshold voltage during handling. This is not usually a problem after the device has been installed in a properly designed circuit.
FETs often have a very low 'on' resistance and have a high 'off' resistance. However the intermediate resistances are significant, and so FETs can dissipate large amounts of power while switching. Thus efficiency can put a premium on switching quickly, but this can cause transients that can excite stray inductances and generate significant voltages that can couple to the gate and cause unintentional switching. FET circuits can therefore require very careful layout and can involve trades between switching speed and power dissipation. There is also a trade-off between voltage rating and 'on' resistance, so high voltage FETs have a relatively high 'on' resistance and hence conduction losses.
Uses[edit]
The most commonly used FET is the MOSFET. The CMOS (complementary metal oxide semiconductor) process technology is the basis for modern digital integrated circuits. This process technology uses an arrangement where the (usually "enhancement-mode") p-channel MOSFET and n-channel MOSFET are connected in series such that when one is ON, the other is OFF.
In FETs, electrons can flow in either direction through the channel when operated in the linear mode. The naming convention of drain terminal and source terminal is somewhat arbitrary, as the devices are typically (but not always) built symmetrically from source to drain. This makes FETs suitable for switching analog signals between paths (multiplexing). With this concept, one can construct a solid-state mixing board, for example.
A common use of the FET is as an amplifier. For example, due to its large input resistance and low output resistance, it is effective as a buffer in common-drain (source follower) configuration.
IGBTs are used in switching internal combustion engine ignition coils, where fast switching and voltage blocking capabilities are important.
Source-gated transistor[edit]
Source-gated transistors are more robust to manufacturing and environmental issues in large-area electronics such as display screens, but are slower in operation than FETs.[21]
See also[edit]
Chemical field-effect transistor
FET amplifier
FlowFET
Multigate device, especially FinFET
References[edit]
Jump up ^ Junction Field-Effect Devices, Semiconductor Devices for Power Conditioning, 1982
Jump up ^ 1960 - Metal Oxide Semiconductor (MOS) Transistor Demonstrated - The Silicon Engine | Computer History Museum
Jump up ^ Jacob Millman (1985). Electronic devices and circuits. Singapore: McGraw-Hill International. p. 397. ISBN 0-07-085505-6.
^ Jump up to: a b Millman (1985). Electronic devices and circuits. Singapore: McGraw-Hill. pp. 384–385. ISBN 0-07-085505-6.
Jump up ^ C Galup-Montoro; Schneider MC (2007). MOSFET modeling for circuit analysis and design. London/Singapore: World Scientific. p. 83. ISBN 981-256-810-7.
Jump up ^ Norbert R Malik (1995). Electronic circuits: analysis, simulation, and design. Englewood Cliffs, NJ: Prentice Hall. pp. 315–316. ISBN 0-02-374910-5.
Jump up ^ RR Spencer; Ghausi MS (2001). Microelectronic circuits. Upper Saddle River NJ: Pearson Education/Prentice-Hall. p. 102. ISBN 0-201-36183-3.
Jump up ^ A. S. Sedra; K.C. Smith (2004). Microelectronic circuits (Fifth ed.). New York: Oxford. p. 552. ISBN 0-19-514251-9.
Jump up ^ PR Gray; PJ Hurst; SH Lewis; RG Meyer (2001). Analysis and design of analog integrated circuits (Fourth ed.). New York: Wiley. pp. §1.5.2 p. 45. ISBN 0-471-32168-0.
Jump up ^ IBM creates first graphene based integrated circuit
Jump up ^ Lin, Y.-M.; Valdes-Garcia, A.; Han, S.-J.; Farmer, D. B.; Sun, Y; Wu, Y; Dimitrakopoulos, C.; Grill, A; Avouris, P & Jenkins, K. A. (2011). "Wafer-Scale Graphene Integrated Circuit". Science. 332: 1294–1297. doi:10.1126/science.1204428. PMID 21659599.
Jump up ^ Flexible graphene transistor sets new records - physicsworld.com
Jump up ^ freepatentsonline.com, HIGFET and method - Motorola
Jump up ^ Ionescu, A. M.; Riel, H. (2011). "Tunnel field-effect transistors as energy-efficient electronic switches". Nature. 479 (7373): 329–337. doi:10.1038/nature10679. PMID 22094693.
Jump up ^ Poghossianb, Arshak (2002). "Recent advances in biologically sensitive field-effect transistors (BioFETs)". Analyst. 127: 1137–1151. doi:10.1039/B204444G.
Jump up ^ sciencedaily.com
Jump up ^ Sarvari H, et al. (2011). "Frequency analysis of graphene nanoribbon FET by Non-Equilibrium Green's Function in mode space". Physica E: Low-dimensional Systems and Nanostructures. 43 (8): 1509–1513. doi:10.1016/j.physe.2011.04.018.
Jump up ^ Jerzy Ruzyllo (2016-09-15). Semiconductor Glossary: A Resource for Semiconductor Community. World Scientific. pp. 244–. ISBN 978-981-4749-56-5.
Jump up ^ physics.lbl.gov
Jump up ^ Allen Mottershead (2004). Electronic devices and circuits. New Delhi: Prentice-Hall of India. ISBN 81-203-0124-2.
Jump up ^ "Source-gated transistors for order-of-magnitude performance improvements in thin-film digital circuits"
External links[edit]
Wikimedia Commons has media related to Field-effect Transistors.
PBS The Field Effect Transistor
Junction Field Effect Transistor
CMOS gate circuitry
Winning the Battle Against Latchup in CMOS Analog Switches
Field Effect Transistors in Theory and Practice
The Field Effect Transistor as a Voltage Controlled Resistor
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Authority control
LCCN: sh85048099
GND: 4131472-4
NDL: 01150221
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