Введение
Свойство, при котором увеличение напряжения приводит к уменьшению тока. При работе увеличение тока через флуоресцентную лампу вызывает падение напряжения на ней. Если бы лампа была подключена непосредственно к сети, падение напряжения привело бы к возрастанию тока, что вызвало бы дуговой разряд и её разрушение. Это отличается от обычного резистора, в котором увеличение приложенного напряжения вызывает пропорциональное увеличение тока согласно закону Ома, что приводит к положительному сопротивлению. В то время как положительное сопротивление потребляет мощность от протекающего через него тока, отрицательное сопротивление генерирует мощность. При определенных условиях оно может увеличивать мощность электрического сигнала, усиливая его. Отрицательное сопротивление – это необычное свойство, встречающееся в нескольких нелинейных электронных компонентах. В нелинейном устройстве можно определить два типа сопротивления: «статическое» или «абсолютное сопротивление» – отношение напряжения к току, и дифференциальное сопротивление – отношение изменения напряжения к вызванному изменению тока. Термин «отрицательное сопротивление» означает отрицательное дифференциальное сопротивление (ОДС). Особенно это актуально на микроволновых частотах. Большая часть микроволновой энергии производится с использованием устройств с отрицательным дифференциальным сопротивлением. Они также могут проявлять гистерезис и быть бистабильными, поэтому используются в схемах переключения и памяти. Примеры устройств с отрицательным дифференциальным сопротивлением: туннельные диоды, диоды Ганна и газоразрядные трубки, такие как неоновые лампы и люминесцентные лампы. Кроме того, схемы, содержащие усиливающие элементы, такие как транзисторы и операционные усилители с положительной обратной связью, могут иметь отрицательное дифференциальное сопротивление. Они используются в генераторах и активных фильтрах. Поскольку они нелинейны, устройства с отрицательным сопротивлением имеют более сложное поведение, чем положительные «омические» сопротивления, обычно встречающиеся в электрических цепях. В отличие от большинства положительных сопротивлений, отрицательное сопротивление изменяется в зависимости от напряжения или тока, приложенного к устройству, и устройства с отрицательным сопротивлением могут проявлять отрицательное сопротивление только в ограниченном диапазоне напряжения или тока. Большинство материалов, включая обычные (положительные) сопротивления, встречающиеся в электрических цепях, подчиняются закону Ома: ток через них пропорционален напряжению в широком диапазоне. В нелинейном компоненте вольт-амперная характеристика (ВАХ) не является прямой линией и, следовательно, не подчиняется закону Ома.
[[File:Fluorescent light strip 2 tube. JPG|thumb|upright=1.3|Fluorescent lamp, a device with negative differential resistance. In operation, an increase in current through the fluorescent tube causes a drop in voltage across it. If the tube were connected directly to the power line, the falling tube voltage would cause more and more current to flow, causing it to arc flash and destroy itself. This is in contrast to an ordinary resistor in which an increase of applied voltage causes a proportional increase in current due to Ohm's law, resulting in a positive resistance. While a positive resistance consumes power from current passing through it, a negative resistance produces power. Under certain conditions it can increase the power of an electrical signal, amplifying it. Negative resistance is an uncommon property which occurs in a few nonlinear electronic components. In a nonlinear device, two types of resistance can be defined: 'static' or 'absolute resistance', the ratio of voltage to current , and differential resistance, the ratio of a change in voltage to the resulting change in current The term negative resistance means negative differential resistance (NDR), In general, a negative differential resistance is a two terminal component which can amplify, converting DC power applied to its terminals to AC output power to amplify an AC signal applied to the same terminals. particularly at microwave frequencies. Most microwave energy is produced with negative differential resistance devices. They can also have hysteresis and be bistable, and so are used in switching and memory circuits. Examples of devices with negative differential resistance are tunnel diodes, Gunn diodes, and gas discharge tubes such as neon lamps, and fluorescent lights. In addition, circuits containing amplifying devices such as transistors and op amps with positive feedback can have negative differential resistance. These are used in oscillators and active filters. Because they are nonlinear, negative resistance devices have a more complicated behavior than the positive "ohmic" resistances usually encountered in electric circuits. Unlike most positive resistances, negative resistance varies depending on the voltage or current applied to the device, and negative resistance devices can only have negative resistance over a limited portion of their voltage or current range. Most materials, including the ordinary (positive) resistances encountered in electrical circuits, obey Ohm's law; the current through them is proportional to the voltage over a wide range. In a nonlinear component the I–V curve is not a straight line, so it does not obey Ohm's law. which are equal for ohmic resistances:
thumb|The quadrants of the I–V plane, showing regions representing passive devices (white) and active devices (red)
Static resistance (also called chordal resistance, absolute resistance or just resistance) – This is the common definition of resistance; the voltage divided by the current: However this term is never used in practice, because the term "resistance" is only applied to passive components. Static resistance determines the power dissipation in a component. Differential resistance (also called dynamic, It is measured in siemens (formerly mho) which is the conductance of a resistor with a resistance of one ohm. while a positive resistance will have a positive conductance. Therefore, from the passive sign convention above, conventional current (flow of positive charge) is through the device from the positive to the negative terminal, in the direction of the electric field E (decreasing potential). and these devices can be divided into two categories depending on whether they get their power from an internal source or from their port:
thumb
Passive negative differential resistance devices (fig. 2 above): These are the most well known type of "negative resistances"; passive two terminal components whose intrinsic I–V curve has a downward "kink", causing the current to decrease with increasing voltage over a limited range. (fig. 3 above). Although the "static" or "absolute" resistance of active devices (power sources) can be considered negative (see Negative static resistance section below) most ordinary power sources (AC or DC), such as batteries, generators, and (non positive feedback) amplifiers, have positive differential resistance (their source resistance). Therefore, these devices cannot function as one port amplifiers or have the other capabilities of negative differential resistances.
Квадранты плоскости ВАХ, показывающие области, представляющие пассивные (белые) и активные (красные) устройства.
[[File:Fluorescent light strip 2 tube. JPG|thumb|upright=1.3|Fluorescent lamp, a device with negative differential resistance. In operation, an increase in current through the fluorescent tube causes a drop in voltage across it. If the tube were connected directly to the power line, the falling tube voltage would cause more and more current to flow, causing it to arc flash and destroy itself. This is in contrast to an ordinary resistor in which an increase of applied voltage causes a proportional increase in current due to Ohm's law, resulting in a positive resistance. While a positive resistance consumes power from current passing through it, a negative resistance produces power. Under certain conditions it can increase the power of an electrical signal, amplifying it. Negative resistance is an uncommon property which occurs in a few nonlinear electronic components. In a nonlinear device, two types of resistance can be defined: 'static' or 'absolute resistance', the ratio of voltage to current , and differential resistance, the ratio of a change in voltage to the resulting change in current The term negative resistance means negative differential resistance (NDR), In general, a negative differential resistance is a two terminal component which can amplify, converting DC power applied to its terminals to AC output power to amplify an AC signal applied to the same terminals. particularly at microwave frequencies. Most microwave energy is produced with negative differential resistance devices. They can also have hysteresis and be bistable, and so are used in switching and memory circuits. Examples of devices with negative differential resistance are tunnel diodes, Gunn diodes, and gas discharge tubes such as neon lamps, and fluorescent lights. In addition, circuits containing amplifying devices such as transistors and op amps with positive feedback can have negative differential resistance. These are used in oscillators and active filters. Because they are nonlinear, negative resistance devices have a more complicated behavior than the positive "ohmic" resistances usually encountered in electric circuits. Unlike most positive resistances, negative resistance varies depending on the voltage or current applied to the device, and negative resistance devices can only have negative resistance over a limited portion of their voltage or current range. Most materials, including the ordinary (positive) resistances encountered in electrical circuits, obey Ohm's law; the current through them is proportional to the voltage over a wide range. In a nonlinear component the I–V curve is not a straight line, so it does not obey Ohm's law. which are equal for ohmic resistances:
thumb|The quadrants of the I–V plane, showing regions representing passive devices (white) and active devices (red)
Static resistance (also called chordal resistance, absolute resistance or just resistance) – This is the common definition of resistance; the voltage divided by the current: However this term is never used in practice, because the term "resistance" is only applied to passive components. Static resistance determines the power dissipation in a component. Differential resistance (also called dynamic, It is measured in siemens (formerly mho) which is the conductance of a resistor with a resistance of one ohm. while a positive resistance will have a positive conductance. Therefore, from the passive sign convention above, conventional current (flow of positive charge) is through the device from the positive to the negative terminal, in the direction of the electric field E (decreasing potential). and these devices can be divided into two categories depending on whether they get their power from an internal source or from their port:
thumb
Passive negative differential resistance devices (fig. 2 above): These are the most well known type of "negative resistances"; passive two terminal components whose intrinsic I–V curve has a downward "kink", causing the current to decrease with increasing voltage over a limited range. (fig. 3 above). Although the "static" or "absolute" resistance of active devices (power sources) can be considered negative (see Negative static resistance section below) most ordinary power sources (AC or DC), such as batteries, generators, and (non positive feedback) amplifiers, have positive differential resistance (their source resistance). Therefore, these devices cannot function as one port amplifiers or have the other capabilities of negative differential resistances.
Статическое сопротивление (также называемое хордовым сопротивлением, абсолютным сопротивлением или просто сопротивлением) – это общепринятое определение сопротивления: напряжение, деленное на ток. Однако этот термин редко используется на практике, поскольку термин «сопротивление» обычно применяется только к пассивным компонентам. Статическое сопротивление определяет рассеиваемую мощность в компоненте. Дифференциальное сопротивление (также называемое динамическим) измеряется в сименсах (ранее в мго), что является проводимостью резистора с сопротивлением в один ом, в то время как положительное сопротивление имеет положительную проводимость. Таким образом, исходя из вышеупомянутой пассивной конвенции о знаках, обычный ток (поток положительного заряда) проходит через устройство от положительного к отрицательному выводу, в направлении электрического поля E (уменьшающегося потенциала). Эти устройства можно разделить на две категории в зависимости от того, получают ли они энергию из внутреннего источника или от своих выводов:
[[File:Fluorescent light strip 2 tube. JPG|thumb|upright=1.3|Fluorescent lamp, a device with negative differential resistance. In operation, an increase in current through the fluorescent tube causes a drop in voltage across it. If the tube were connected directly to the power line, the falling tube voltage would cause more and more current to flow, causing it to arc flash and destroy itself. This is in contrast to an ordinary resistor in which an increase of applied voltage causes a proportional increase in current due to Ohm's law, resulting in a positive resistance. While a positive resistance consumes power from current passing through it, a negative resistance produces power. Under certain conditions it can increase the power of an electrical signal, amplifying it. Negative resistance is an uncommon property which occurs in a few nonlinear electronic components. In a nonlinear device, two types of resistance can be defined: 'static' or 'absolute resistance', the ratio of voltage to current , and differential resistance, the ratio of a change in voltage to the resulting change in current The term negative resistance means negative differential resistance (NDR), In general, a negative differential resistance is a two terminal component which can amplify, converting DC power applied to its terminals to AC output power to amplify an AC signal applied to the same terminals. particularly at microwave frequencies. Most microwave energy is produced with negative differential resistance devices. They can also have hysteresis and be bistable, and so are used in switching and memory circuits. Examples of devices with negative differential resistance are tunnel diodes, Gunn diodes, and gas discharge tubes such as neon lamps, and fluorescent lights. In addition, circuits containing amplifying devices such as transistors and op amps with positive feedback can have negative differential resistance. These are used in oscillators and active filters. Because they are nonlinear, negative resistance devices have a more complicated behavior than the positive "ohmic" resistances usually encountered in electric circuits. Unlike most positive resistances, negative resistance varies depending on the voltage or current applied to the device, and negative resistance devices can only have negative resistance over a limited portion of their voltage or current range. Most materials, including the ordinary (positive) resistances encountered in electrical circuits, obey Ohm's law; the current through them is proportional to the voltage over a wide range. In a nonlinear component the I–V curve is not a straight line, so it does not obey Ohm's law. which are equal for ohmic resistances:
thumb|The quadrants of the I–V plane, showing regions representing passive devices (white) and active devices (red)
Static resistance (also called chordal resistance, absolute resistance or just resistance) – This is the common definition of resistance; the voltage divided by the current: However this term is never used in practice, because the term "resistance" is only applied to passive components. Static resistance determines the power dissipation in a component. Differential resistance (also called dynamic, It is measured in siemens (formerly mho) which is the conductance of a resistor with a resistance of one ohm. while a positive resistance will have a positive conductance. Therefore, from the passive sign convention above, conventional current (flow of positive charge) is through the device from the positive to the negative terminal, in the direction of the electric field E (decreasing potential). and these devices can be divided into two categories depending on whether they get their power from an internal source or from their port:
thumb
Passive negative differential resistance devices (fig. 2 above): These are the most well known type of "negative resistances"; passive two terminal components whose intrinsic I–V curve has a downward "kink", causing the current to decrease with increasing voltage over a limited range. (fig. 3 above). Although the "static" or "absolute" resistance of active devices (power sources) can be considered negative (see Negative static resistance section below) most ordinary power sources (AC or DC), such as batteries, generators, and (non positive feedback) amplifiers, have positive differential resistance (their source resistance). Therefore, these devices cannot function as one port amplifiers or have the other capabilities of negative differential resistances.
Пассивные устройства с отрицательным дифференциальным сопротивлением: это наиболее известный тип «отрицательных сопротивлений» – пассивные двухполюсные компоненты, чья внутренняя ВАХ имеет нисходящий «изгиб», вызывающий уменьшение тока при увеличении напряжения в ограниченном диапазоне. Хотя «статическое» или «абсолютное» сопротивление активных устройств (источников питания) может считаться отрицательным, большинство обычных источников питания (постоянного или переменного тока), таких как батареи, генераторы и усилители (без положительной обратной связи), имеют положительное дифференциальное сопротивление (их выходное сопротивление). Поэтому эти устройства не могут функционировать как однопортовые усилители или обладать другими возможностями устройств с отрицательным дифференциальным сопротивлением.
[[File:Fluorescent light strip 2 tube. JPG|thumb|upright=1.3|Fluorescent lamp, a device with negative differential resistance. In operation, an increase in current through the fluorescent tube causes a drop in voltage across it. If the tube were connected directly to the power line, the falling tube voltage would cause more and more current to flow, causing it to arc flash and destroy itself. This is in contrast to an ordinary resistor in which an increase of applied voltage causes a proportional increase in current due to Ohm's law, resulting in a positive resistance. While a positive resistance consumes power from current passing through it, a negative resistance produces power. Under certain conditions it can increase the power of an electrical signal, amplifying it. Negative resistance is an uncommon property which occurs in a few nonlinear electronic components. In a nonlinear device, two types of resistance can be defined: 'static' or 'absolute resistance', the ratio of voltage to current , and differential resistance, the ratio of a change in voltage to the resulting change in current The term negative resistance means negative differential resistance (NDR), In general, a negative differential resistance is a two terminal component which can amplify, converting DC power applied to its terminals to AC output power to amplify an AC signal applied to the same terminals. particularly at microwave frequencies. Most microwave energy is produced with negative differential resistance devices. They can also have hysteresis and be bistable, and so are used in switching and memory circuits. Examples of devices with negative differential resistance are tunnel diodes, Gunn diodes, and gas discharge tubes such as neon lamps, and fluorescent lights. In addition, circuits containing amplifying devices such as transistors and op amps with positive feedback can have negative differential resistance. These are used in oscillators and active filters. Because they are nonlinear, negative resistance devices have a more complicated behavior than the positive "ohmic" resistances usually encountered in electric circuits. Unlike most positive resistances, negative resistance varies depending on the voltage or current applied to the device, and negative resistance devices can only have negative resistance over a limited portion of their voltage or current range. Most materials, including the ordinary (positive) resistances encountered in electrical circuits, obey Ohm's law; the current through them is proportional to the voltage over a wide range. In a nonlinear component the I–V curve is not a straight line, so it does not obey Ohm's law. which are equal for ohmic resistances:
thumb|The quadrants of the I–V plane, showing regions representing passive devices (white) and active devices (red)
Static resistance (also called chordal resistance, absolute resistance or just resistance) – This is the common definition of resistance; the voltage divided by the current: However this term is never used in practice, because the term "resistance" is only applied to passive components. Static resistance determines the power dissipation in a component. Differential resistance (also called dynamic, It is measured in siemens (formerly mho) which is the conductance of a resistor with a resistance of one ohm. while a positive resistance will have a positive conductance. Therefore, from the passive sign convention above, conventional current (flow of positive charge) is through the device from the positive to the negative terminal, in the direction of the electric field E (decreasing potential). and these devices can be divided into two categories depending on whether they get their power from an internal source or from their port:
thumb
Passive negative differential resistance devices (fig. 2 above): These are the most well known type of "negative resistances"; passive two terminal components whose intrinsic I–V curve has a downward "kink", causing the current to decrease with increasing voltage over a limited range. (fig. 3 above). Although the "static" or "absolute" resistance of active devices (power sources) can be considered negative (see Negative static resistance section below) most ordinary power sources (AC or DC), such as batteries, generators, and (non positive feedback) amplifiers, have positive differential resistance (their source resistance). Therefore, these devices cannot function as one port amplifiers or have the other capabilities of negative differential resistances.
Осцилляторы обратной связи
Если LC-контур подключен ко входу усилителя с положительной обратной связью, подобного описанному выше, отрицательное дифференциальное входное сопротивление может компенсировать положительное сопротивление потерь, присущее резонансному контуру. Это создаст, по сути, резонансный контур с нулевым активным сопротивлением (полюса на оси jω). Данная модель отрицательного сопротивления представляет собой альтернативный способ анализа работы генератора на обратной связи.
История
Отрицательное сопротивление впервые было обнаружено при исследовании электрических дуг, которые использовались для освещения в XIX веке. В 1881 году Альфред Ниауде заметил, что напряжение на дуговых электродах временно уменьшалось при увеличении тока дуги, однако многие исследователи считали это вторичным эффектом, вызванным температурой. Начиная с 1895 года Герта Айртон, развивая исследования своего мужа Уильяма с помощью серии кропотливых экспериментов по измерению вольт-амперной характеристики (ВАХ) дуг, установила, что на кривой имеются участки с отрицательным наклоном, что вызвало споры. Фрит и Роджерс в 1896 году, при поддержке Айртонов, а в том же году Элиу Томсон построил генератор на отрицательном сопротивлении, подключив LC-контур к электродам дуги, что, возможно, было первым примером электронного генератора. Уильям Дадделл, ученик Айртона в Лондонском центральном техническом колледже, привлек внимание общественности к генератору на дуге Томсона, изобретя радиопередатчик на дуге Пулсена, который широко использовался до 1920-х годов. В вакуумной лампе, когда электроны сталкиваются с пластинчатым электродом, они могут выбивать дополнительные электроны с поверхности внутрь лампы. Это представляет собой ток, направленный от пластины, уменьшая анодный ток. Он также был одним из первых, кто сообщил об отрицательной ёмкости и индуктивности, вместе с Г. В. Пикардом. Они заметили, что когда переходы смещались постоянным напряжением для повышения их чувствительности в качестве радиодетекторов, они иногда начинали спонтанно генерировать колебания. Он использовал их для создания твердотельных усилителей, генераторов, усиливающих и регенеративных радиоприемников за 25 лет до изобретения транзистора. Позже он даже построил супергетеродинный приемник. Благодаря меньшей паразитной ёмкости, чем у вакуумных ламп из-за небольшого размера переходов, диоды могут работать на более высоких частотах, а туннельные диодные генераторы оказались способны генерировать мощность на микроволновых частотах, превышающих диапазон обычных вакуумных ламп. Его изобретение стимулировало поиск других полупроводниковых приборов с отрицательным сопротивлением для использования в качестве микроволновых генераторов, что привело к открытию диодов IMPATT, диодов Gunn, диодов TRAPATT и других. В 1969 году Курокава вывел условия устойчивости в схемах с отрицательным сопротивлением. В настоящее время генераторы на диодах с отрицательным дифференциальным сопротивлением являются наиболее широко используемыми источниками микроволновой энергии, и в последние десятилетия было открыто множество новых приборов с отрицательным сопротивлением.