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第3行： − + − Alarm or panic can sometimes be spread by positive feedback among a herd of animals to cause a [[stampede.]] − 有时，警报或恐慌会通过正反馈在一群动物之间传播，从而引起踩踏事件。+ − + 第17行：
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第25行： − + − + − + + + + − Both concepts play an important role in science and engineering, including biology, chemistry, and cybernetics.+ − <ref name=theorymodelling/>这两个概念在科学和工程中发挥着重要作用，包括生物学、化学和控制论。 − − − − Mathematically, positive feedback is defined as a positive [[loop gain]] around a closed loop of cause and effect.<ref name=zuckerman/><ref name=theorymodelling> − 数学上，正反馈被定义为围绕一个闭合因果循环的正环增益。<ref name=zuckerman/><ref name=theorymodelling> − − That is, positive feedback is in phase with the input, in the sense that it adds to make the input larger. − − 也就是说，正反馈与输入是同步的，意味着正反馈增加了输入使其更大。 − − − Positive feedback tends to cause system instability. When the loop gain is positive and above 1, there will typically be exponential growth, increasing oscillations, chaotic behavior or other divergences from equilibrium. System parameters will typically accelerate towards extreme values, which may damage or destroy the system, or may end with the system latched into a new stable state. Positive feedback may be controlled by signals in the system being filtered，damped or limited，or it can be cancelled or reduced by adding negative feedback. − − 正反馈容易导致系统不稳定。当环增益为正且大于1时，通常会出现指数增长、振荡加剧、混沌行为或其它偏离平衡的现象。系统参数通常会向极端值加速靠近，这可能会损坏或摧毁系统，或者可能以系统进入新的稳定状态而结束。正反馈可以通过系统中的信号被滤波器过滤、阻尼或最大值和最小值限制来控制，也可以通过增加负反馈来抵消或减少。 − − Positive feedback is used in digital electronics to force voltages away from intermediate voltages into '0' and '1' states. On the other hand, thermal runaway is a type of positive feedback that can destroy semiconductor junctions. Positive feedback in chemical reactions can increase the rate of reactions, and in some cases can lead to explosions. Positive feedback in mechanical design causes tipping-point, or 'over-centre', mechanisms to snap into position, for example in switches and locking pliers. Out of control, it can cause bridges to collapse. Positive feedback in economic systems can cause boom-then-bust cycles. A familiar example of positive feedback is the loud squealing or howling sound produced by audio feedback in public address systems: the microphone picks up sound from its own loudspeakers, amplifies it, and sends it through the speakers again. − − 正反馈用于数字电子产品中，以迫使电压从中间电压变为“ 0”和“ 1”状态。另一方面，热失控是一种正反馈，可以破坏半导体结。化学反应中的正反馈可以提高反应速度，在某些情况下可以导致爆炸。机械设计中的正反馈会导致临界点或 "过中心"，使机械装置卡住位置，例如开关和锁紧钳。如果失控，会导致桥梁倒塌。经济系统中的正反馈会造成先繁荣后萧条的循环。正反馈的一个熟悉的例子是公共广播系统中的音频反馈所产生的响亮的尖叫声或嚎叫声：麦克风从自己的扬声器中拾取声音，将其放大，然后再通过扬声器发送。 − − [[File:Positive Feedback Diagram (2).svg|thumb|[[Platelet]] clotting demonstrates positive feedback. The damaged blood vessel wall releases chemicals that initiate the formation of a blood clot through platelet congregation. As more platelets gather, more chemicals are released that speed up the process. The process gets faster and faster until the blood vessel wall is completely sealed and the positive feedback loop has ended. The exponential form of the graph illustrates the positive feedback mechanism. ]] − − Platelet clotting demonstrates positive feedback. The damaged blood vessel wall releases chemicals that initiate the formation of a blood clot through platelet congregation. As more platelets gather, more chemicals are released that speed up the process. The process gets faster and faster until the blood vessel wall is completely sealed and the positive feedback loop has ended. The exponential form of the graph illustrates the positive feedback mechanism. − − 血小板凝血表现为正反馈。受损的血管壁会释放化学物质，通过血小板聚集启动血栓的形成。随着越来越多的血小板聚集，更多的化学物质被释放出来，加快了这个过程。这个过程越来越快，直到血管壁完全密封，正反馈循环结束。 图中的指数形式说明了正反馈机制。 − − == Overview == − 总览 − − Positive feedback enhances or amplifies an effect by it having an influence on the process which gave rise to it. For example, when part of an electronic output signal returns to the input, and is in phase with it, the system [[Gain (electronics)|gain]] is increased.<ref>{{cite web|title=Positive feedback|url=http://www.oxforddictionaries.com/definition/english/positive-feedback|work=Oxford English Dictionary|publisher=Oxford University Press|accessdate=15 April 2014|url-status=live|archiveurl=https://web.archive.org/web/20140302160045/http://www.oxforddictionaries.com/definition/english/positive-feedback|archivedate=2 March 2014}}<br> − − 正反馈通过对产生该效应的过程产生影响来增强或放大该效应。例如，当部分电子输出信号返回到输入端，并与输入端同相，系统增益就会增加<ref>{{cite web|title=Positive feedback|url=http://www.oxforddictionaries.com/definition/english/positive-feedback|work=Oxford English Dictionary|publisher=Oxford University Press|accessdate=15 April 2014|url-status=live|archiveurl=https://web.archive.org/web/20140302160045/http://www.oxforddictionaries.com/definition/english/positive-feedback|archivedate=2 March 2014}}<br> − 。 − − </ref> The feedback from the outcome to the originating process can be direct, or it can be via other state variables.<ref name=theorymodelling/> Such systems can give rich qualitative behaviors, but whether the feedback is instantaneously positive or negative in sign has an extremely important influence on the results. − </ref> T结果对始发过程的反馈可以是直接的，也可以通过其他状态变量。<ref name=theorymodelling/> − 这样的系统可以给出丰富的定性行为，但反馈的瞬时信号是正向还是负向，对结果有极其重要的影响。 − − <ref name=theorymodelling/> Positive feedback reinforces and negative feedback moderates the original process. ''Positive'' and ''negative'' in this sense refer to loop gains greater than or less than zero, and do not imply any [[value judgement]]s as to the desirability of the outcomes or effects.<ref>{{cite web|title=Feedback|url=http://metadesigners.org/Feedback-Glossary|work=Glossary|publisher=Metadesigners Network|accessdate=15 April 2014|url-status=live|archiveurl=https://web.archive.org/web/20140416183720/http://metadesigners.org/Feedback-Glossary|archivedate=16 April 2014}}</ref> A key feature of positive feedback is thus that small disturbances get bigger. When a change occurs in a system, positive feedback causes further change, in the same direction. − − <ref name=theorymodelling/> 正反馈强化原过程，负反馈调节原过程。''正''和''负''在这个意义上指的是大于或小于零的循环收益，并不意味着对结果或效果的可取性有任何价值判断。 − .<ref>{{cite web|title=Feedback|url=http://metadesigners.org/Feedback-Glossary|work=Glossary|publisher=Metadesigners Network|accessdate=15 April 2014|url-status=live|archiveurl=https://web.archive.org/web/20140416183720/http://metadesigners.org/Feedback-Glossary|archivedate=16 April 2014}}</ref> 因此，正反馈的一个重要特点是小扰动变大。当系统发生变化时，正反馈会引起进一步的同方向变化。 第81行：
第41行： − + − A basic feedback system can be represented by this block diagram. In the diagram the + symbol is an adder and A and B are arbitrary causal functions.+ − − 图中是一个简单的反馈回路。 如果环增益AB为正值，则存在'正'或'再生'反馈的条件。+ − + − + 第98行：
第57行： − + − 因此根据反馈，状态变化可以是收敛的，也可以是发散的。 正反馈的结果是增强变化，因此小的扰动可能导致大的变化。+ + − 一个处于平衡状态的系统，其当前状态的任何变化都有正反馈，它可能是不稳定的，在这种情况下，系统被称为不稳定平衡。使这种系统远离其平衡状态的力的大小是状态与平衡状态之间的距离的递增函数。+ + 第113行：
第74行： − 迟滞现象+ − + − + − 迟滞现象会导致输出值取决于输入的历史记录 − + − + − − 在施密特触发器电路中，对放大器的非反相输入的反馈直接将输出从外加电压推向放大器所能产生的最大或最小电压。 第132行：
第90行： − ::"Positive feedback loops are sources of growth, explosion, erosion, and collapse in systems. A system with an unchecked positive loop ultimately will destroy itself. That’s why there are so few of them. Usually a negative loop will kick in sooner or later."<ref name=meadows>+ + − “正反馈循环是系统增长、爆炸、侵蚀和崩溃的源头。如果一个系统的正循环不受控制，最终将会自我毁灭。这就是为什么很少有这样的系统。通常情况下，负面循环迟早会发生。”<ref name=meadows>+ − Donella Meadows, [http://www.sustainabilityinstitute.org/pubs/Leverage_Points.pdf ''Leverage Points: Places to Intervene in a System''] {{webarchive|url=https://web.archive.org/web/20131008160618/http://www.sustainabilityinstitute.org/pubs/Leverage_Points.pdf |date=2013-10-08 }}, 1999</ref>+ − 磁滞现象，即起点影响系统的终点，可以通过正反馈产生。当反馈循环的增益高于1时，那么输出就会远离输入：如果高于输入，则向最近的正极限移动，而如果低于输入，则向最近的负极限移动。+ − 一旦达到极限，它就会稳定下来。但是，如果输入超过极限，那么反馈将改变符号，输出将向相反的方向移动，直到达到相反的极限。因此，该系统表现出双稳态行为。+ − 术语学+ − 在二战前，正反馈和负反馈这两个名词最早应用于反馈。20世纪20年代，随着再生电路的问世，正反馈的概念已经出现。+ − + 第164行：
第123行： − + − + − − − + 第178行：
第135行： − + − 一个老式的再生无线电接收器。由于使用正反馈的控制，真空管或阀门（中心）就可以产生足够的放大效果。+ 第234行：
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前两部分
{{short description|Destabilising process that occurs in a feedback loop}}
{{short description|Destabilising process that occurs in a feedback loop}}
[[File:Herdwick Stampede.jpg|thumb|right|Alarm or panic can sometimes be spread by positive feedback among a herd of animals to cause a [[stampede]].]]
[[File:Herdwick Stampede.jpg|thumb|right|Alarm or panic can sometimes be spread by positive feedback among a herd of animals to cause a [[stampede]].|链接=Special:FilePath/Herdwick_Stampede.jpg]]
【图1：Alarm or panic can sometimes be spread by positive feedback among a herd of animals to cause a [[stampede.]] 有时，警报或恐慌会通过正反馈在一群动物之间传播，从而引起踩踏事件。】
[[File:Stampede loop.png|thumb|[[Causal loop diagram]] that depicts the causes of a stampede as a positive feedback loop.]]
[[File:Stampede loop.png|thumb|[[Causal loop diagram]] that depicts the causes of a stampede as a positive feedback loop.|链接=Special:FilePath/Stampede_loop.png]]
[[Causal loop diagram that depicts the causes of a stampede as a positive feedback loop.]]
[[Causal loop diagram that depicts the causes of a stampede as a positive feedback loop.]]
[[File:Birmingham Northern Rock bank run 2007.jpg|thumb|right|In sociology a [[network effect]] can quickly create the positive feedback of a [[bank run]]. The above photo is of the [[Nationalisation of Northern Rock#Run on the bank|UK Northern Rock 2007 bank run]].]]
[[File:Birmingham Northern Rock bank run 2007.jpg|thumb|right|In sociology a [[network effect]] can quickly create the positive feedback of a [[bank run]]. The above photo is of the [[Nationalisation of Northern Rock#Run on the bank|UK Northern Rock 2007 bank run]].|链接=Special:FilePath/Birmingham_Northern_Rock_bank_run_2007.jpg]]
In sociology a [[network effect can quickly create the positive feedback of a bank run. The above photo is of the UK Northern Rock 2007 bank run.]]
In sociology a [[network effect can quickly create the positive feedback of a bank run. The above photo is of the UK Northern Rock 2007 bank run.]]
'''Positive feedback''' ('''exacerbating feedback''', '''self-reinforcing feedback''') is a process that occurs in a [[feedback loop]] which exacerbates the effects of a small disturbance. That is, the effects of a perturbation on a system include an increase in the magnitude of the perturbation.
'''Positive feedback''' ('''exacerbating feedback''', '''self-reinforcing feedback''') is a process that occurs in a [[feedback loop]] which exacerbates the effects of a small disturbance. That is, the effects of a perturbation on a system include an increase in the magnitude of the perturbation.
Positive feedback (exacerbating feedback, self-reinforcing feedback) is a process that occurs in a feedback loop which exacerbates the effects of a small disturbance. That is, the effects of a perturbation on a system include an increase in the magnitude of the perturbation. That is, A produces more of B which in turn produces more of A. In contrast, a system in which the results of a change act to reduce or counteract it has negative feedback.
Positive feedback (exacerbating feedback, self-reinforcing feedback) is a process that occurs in a feedback loop which exacerbates the effects of a small disturbance. That is, the effects of a perturbation on a system include an increase in the magnitude of the perturbation. That is, A produces more of B which in turn produces more of A. In contrast, a system in which the results of a change act to reduce or counteract it has negative feedback.<ref name="theorymodelling" /> Both concepts play an important role in science and engineering, including biology, chemistry, and [[cybernetics]] .
正反馈(加剧反馈，自我强化反馈) 是指在反馈循环中发生的一个过程，它加剧了小扰动的影响, 即一个扰动对系统的影响包括扰动幅度的增大。也就是说，A会产生更多的B，而B又会产生更多的A，相反，一个系统中，变化的结果会减少或抵消变化的结果，这就是负反馈。
正反馈(加剧反馈，自我强化反馈) 是一种在反馈循环中加剧微小扰动影响的过程。也就是说，一个扰动对系统的影响包括它自身扰动幅度的增大。或者说，A会产生更多的B，而B又会产生更多的A，与之相反的是，[[负反馈]]指的是一个系统中，变化的结果会减少或抵消它自己的影响。<ref name="theorymodelling" />这两个概念在科学和工程等领域中发挥着重要作用，包括生物学、化学和控制论。
<ref name=theorymodelling/> Both concepts play an important role in science and engineering, including biology, chemistry, and [[cybernetics]] .<br>
Mathematically, positive feedback is defined as a positive [[loop gain]] around a closed loop of cause and effect.<ref name="zuckerman" /><ref name="theorymodelling">
[[wikipedia:Positive_feedback#cite_note-zuckerman-1|Ben Zuckerman & David Jefferson (1996). ''Human Population and the Environmental Crisis''. Jones & Bartlett Learning. p. 42. ISBN <bdi>9780867209662</bdi>. Archived from the original on 2018-01-06.]]
</ref><ref name="zuckerman" /> The feedback from the outcome to the originating process can be direct, or it can be via other state variables.<ref name="theorymodelling" /> Such systems can give rich qualitative behaviors, but whether the feedback is instantaneously positive or negative in sign has an extremely important influence on the results.
<nowiki></ref></nowiki> <ref name="theorymodelling" /> Positive feedback reinforces and negative feedback moderates the original process. ''Positive'' and ''negative'' in this sense refer to loop gains greater than or less than zero, and do not imply any [[value judgement]]s as to the desirability of the outcomes or effects.<ref name=":0">{{cite web|title=Feedback|url=http://metadesigners.org/Feedback-Glossary|work=Glossary|publisher=Metadesigners Network|accessdate=15 April 2014|url-status=live|archiveurl=https://web.archive.org/web/20140416183720/http://metadesigners.org/Feedback-Glossary|archivedate=16 April 2014}}</ref> A key feature of positive feedback is thus that small disturbances get bigger. When a change occurs in a system, positive feedback causes further change, in the same direction.
在数学上，正反馈被定义为一个环绕在闭合因果循环下的正循环增益。从结果到始发过程的反馈可以是直接的，或者它可以通过其他状态变量。<ref name="theorymodelling" /> 这样的系统可以给出丰富的定性行为，但反馈的瞬时信号是正向还是负向，对结果有极其重要的影响。<ref name="theorymodelling" /> 正反馈强化原过程，而负反馈调节原过程。在这个含义下，''正''和''负''指的是大于或小于零的循环收益，并不代表着最终结果或效果的正负性。<ref name=":0" />因此，正反馈的一个重要特点是小扰动变大。当系统发生变化时，正反馈会引起进一步的同方向变化。
基础
基础
[[File:Ideal feedback model.svg|thumb|A basic feedback system can be represented by this block diagram. In the diagram the + symbol is an adder and A and B are arbitrary [[causal system|causal]] functions.]]
[[File:Ideal feedback model.svg|thumb|A basic feedback system can be represented by this block diagram. In the diagram the + symbol is an adder and A and B are arbitrary [[causal system|causal]] functions.|链接=Special:FilePath/Ideal_feedback_model.svg]]
【图4：A basic feedback system can be represented by this block diagram. In the diagram the + symbol is an adder and A and B are arbitrary causal functions. 一个基本的反馈系统可以用这个框图来表示。在图中，+号是加法器，A和B是任意因果函数。】
一个基本的反馈系统可以用这个框图来表示。在图中，+号是加法器，A和B是任意因果函数。
A simple feedback loop is shown in the diagram. If the loop gain AB is positive, then a condition of ''positive'' or ''regenerative'' feedback exists.
A simple feedback loop is shown in the diagram. If the loop gain AB is positive, then a condition of ''positive'' or ''regenerative'' feedback exists.
图中显示了一个简单的反馈回路。 如果环增益AB为正值，则存在'正'或'再生'反馈的条件。
If the functions A and B are linear and AB is smaller than unity, then the overall system gain from the input to output is finite, but can be very large as AB approaches unity.<ref name=smith> Electronics circuits and devices second edition. Ralph J. Smith</ref> In that case, it can be shown that the overall or "closed loop" gain from input to output is:
If the functions A and B are linear and AB is smaller than unity, then the overall system gain from the input to output is finite, but can be very large as AB approaches unity.<ref name=smith> Electronics circuits and devices second edition. Ralph J. Smith</ref> In that case, it can be shown that the overall or "closed loop" gain from input to output is:
如果函数A和B是线性的，且AB小于1，那么系统从输入到输出的整体增益是有限的，但当AB接近1时，系统的增益可以非常大。<ref name=smith> Electronics circuits and devices second edition. Ralph J. Smith</ref>
在这种情况下，可以表明从输入到输出的整体或 "闭环 "增益为：
如果函数A和B是线性的，且AB小于1，那么系统从输入到输出的整体增益是有限的，但当AB接近1时，系统的增益可以非常大。<ref name="smith"> Electronics circuits and devices second edition. Ralph J. Smith</ref> 在这种情况下，可以表明从输入到输出的整体或 "闭环 "增益为：
:<math>G_c = A/(1-AB)</math>
:<math>G_c = A/(1-AB)</math>
When AB > 1, the system is unstable, so does not have a well-defined gain; the gain may be called infinite.
When AB > 1, the system is unstable, so does not have a well-defined gain; the gain may be called infinite.
当AB>1时，系统是不稳定的，所以不具有明确的增益，增益可称为无限。
当AB>1时，系统是不稳定的，因此不具有明确的增益；增益可称为无限。
Thus depending on the feedback, state changes can be convergent, or divergent. The result of positive feedback is to augment changes, so that small perturbations may result in big changes.
Thus depending on the feedback, state changes can be convergent, or divergent. The result of positive feedback is to augment changes, so that small perturbations may result in big changes.
所以系统状态的变化根据反馈可以是收敛的，也可以是发散的。 而正反馈的结果是增强变化，因此小的扰动就可能导致大的变化。
A system in equilibrium in which there is positive feedback to any change from its current state may be unstable, in which case the system is said to be in an unstable equilibrium. The magnitude of the forces that act to move such a system away from its equilibrium are an increasing function of the "distance" of the state from the equilibrium.
A system in equilibrium in which there is positive feedback to any change from its current state may be unstable, in which case the system is said to be in an unstable equilibrium. The magnitude of the forces that act to move such a system away from its equilibrium are an increasing function of the "distance" of the state from the equilibrium.
对于一个当前处于平衡状态的系统，如果其状态的任何变化都发生了正反馈，从而造成了状态的不稳定，那么这个系统就是一个不稳定平衡的系统。使这种系统远离其平衡状态的力的大小是状态与平衡状态之间的距离的递增函数。
Positive feedback does not necessarily imply instability of an equilibrium, for example stable ''on'' and ''off'' states may exist in positive-feedback architectures.<ref name="ReferenceA">{{cite journal|last1=Lopez-Caamal|first1=Fernando|last2=Middleton|first2=Richard H.|last3=Huber|first3=Heinrich|title=Equilibria and stability of a class of positive feedback loops|journal=Journal of Mathematical Biology|date=February 2014|pages=609–645|doi = 10.1007/s00285-013-0644-z|pmid=23358701|volume=68|issue=3}}</ref>
Positive feedback does not necessarily imply instability of an equilibrium, for example stable ''on'' and ''off'' states may exist in positive-feedback architectures.<ref name="ReferenceA">{{cite journal|last1=Lopez-Caamal|first1=Fernando|last2=Middleton|first2=Richard H.|last3=Huber|first3=Heinrich|title=Equilibria and stability of a class of positive feedback loops|journal=Journal of Mathematical Biology|date=February 2014|pages=609–645|doi = 10.1007/s00285-013-0644-z|pmid=23358701|volume=68|issue=3}}</ref>
=== Hysteresis ===
=== Hysteresis ===
迟滞
{{main|Hysteresis}}
{{main|Hysteresis}}
[[File:Hysteresis sharp curve.svg|thumb|Hysteresis causes the output value to depend on the history of the input]]
[[File:Hysteresis sharp curve.svg|thumb|Hysteresis causes the output value to depend on the history of the input|链接=Special:FilePath/Hysteresis_sharp_curve.svg]]
Hysteresis causes the output value to depend on the history of the input
【图5 Hysteresis causes the output value to depend on the history of the input 迟滞现象会导致输出值取决于输入的历史记录。】
[[File:Op-Amp Schmitt Trigger.svg|thumb|In a [[Schmitt trigger]] circuit, feedback to the non-inverting input of an amplifier pushes the output directly away from the applied voltage towards the maximum or minimum voltage the amplifier can generate.]]
[[File:Op-Amp Schmitt Trigger.svg|thumb|In a [[Schmitt trigger]] circuit, feedback to the non-inverting input of an amplifier pushes the output directly away from the applied voltage towards the maximum or minimum voltage the amplifier can generate.|链接=Special:FilePath/Op-Amp_Schmitt_Trigger.svg]]
In a Schmitt trigger circuit, feedback to the non-inverting input of an amplifier pushes the output directly away from the applied voltage towards the maximum or minimum voltage the amplifier can generate.
【图6 In a Schmitt trigger circuit, feedback to the non-inverting input of an amplifier pushes the output directly away from the applied voltage towards the maximum or minimum voltage the amplifier can generate. 在施密特触发器电路中，利用放大器的非反相输入端口产生的反馈，可以直接将电路的输出从原本的外加电压值推向到放大器所能产生的极值电压。】
In the real world, positive feedback loops typically do not cause ever-increasing growth, but are modified by limiting effects of some sort. According to [[Donella Meadows]]:
In the real world, positive feedback loops typically do not cause ever-increasing growth, but are modified by limiting effects of some sort. According to [[Donella Meadows]]:
在现实世界中，正反馈循环通常不会引起不断增长，而是通过某种限制效应来改变。根据Donella Meadows的说法：
在现实世界中，正反馈循环通常不会引起不断增长，而是通过某种限制效应来改变。根据Donella Meadows的说法：
"Positive feedback loops are sources of growth, explosion, erosion, and collapse in systems. A system with an unchecked positive loop ultimately will destroy itself. That’s why there are so few of them. Usually a negative loop will kick in sooner or later."<ref name="meadows">
“正反馈循环是系统增长、爆炸、侵蚀和崩溃的源头。如果一个系统的正循环不受控制，最终将会自我毁灭。这就是为什么很少有这样的系统。通常情况下，负面循环迟早会发生。”<nowiki><ref name=meadows></nowiki>
Donella Meadows, [http://www.sustainabilityinstitute.org/pubs/Leverage_Points.pdf ''Leverage Points: Places to Intervene in a System''] {{webarchive|url=https://web.archive.org/web/20131008160618/http://www.sustainabilityinstitute.org/pubs/Leverage_Points.pdf |date=2013-10-08 }}, 1999</ref>
正反馈回路是系统增长、爆炸、腐蚀和崩溃的根源。一个系统如果有一个不受控制的正反馈，最终将会自我毁灭。这就是为什么正反馈如此稀少的原因。通常情况下，负反馈迟早会发生。
Hysteresis, in which the starting point affects where the system ends up, can be generated by positive feedback. When the gain of the feedback loop is above 1, then the output moves away from the input: if it is above the input, then it moves towards the nearest positive limit, while if it is below the input then it moves towards the nearest negative limit.
Hysteresis, in which the starting point affects where the system ends up, can be generated by positive feedback. When the gain of the feedback loop is above 1, then the output moves away from the input: if it is above the input, then it moves towards the nearest positive limit, while if it is below the input then it moves towards the nearest negative limit.
[[迟滞]]，即起点影响系统的终点的现象，正是通过正反馈产生的。当反馈循环的增益高于1时，那么输出就会远离输入：如果大于输入，则向最近的正极限移动，而如果小于输入，则向最近的负极限移动。
Once it reaches the limit, it will be stable. However, if the input goes past the limit,{{clarify|date=June 2012}} then the feedback will change sign{{dubious|date=June 2012}} and the output will move in the opposite direction until it hits the opposite limit. The system therefore shows [[bistability|bistable]] behaviour.
Once it reaches the limit, it will be stable. However, if the input goes past the limit,{{clarify|date=June 2012}} then the feedback will change sign{{dubious|date=June 2012}} and the output will move in the opposite direction until it hits the opposite limit. The system therefore shows [[bistability|bistable]] behaviour.
一旦达到极限，它就会稳定下来。但是，如果输入超过极限，那么反馈将改变符号，输出将向相反的方向移动，直到达到相反的极限。因此，该系统表现出[[双稳态行为]]。
== Terminology ==
== Terminology ==
术语的由来
The terms positive and negative were first applied to feedback before World War II. The idea of positive feedback was already current in the 1920s with the introduction of the regenerative circuit.
The terms positive and negative were first applied to feedback before World War II. The idea of positive feedback was already current in the 1920s with the introduction of the regenerative circuit.
正反馈和负反馈这两个名词最早应用于反馈是在二战前。正反馈的概念随着再生电路的问世，在20世纪20年代已经出现。
Friis & Jensen (1924) described regeneration in a set of electronic amplifiers as a case where the "feed-back" action is positive in contrast to negative feed-back action, which they mention only in passing. Harold Stephen Black's classic 1934 paper first details the use of negative feedback in electronic amplifiers. According to Black:
Friis & Jensen (1924) described regeneration in a set of electronic amplifiers as a case where the "feed-back" action is positive in contrast to negative feed-back action, which they mention only in passing. Harold Stephen Black's classic 1934 paper first details the use of negative feedback in electronic amplifiers. According to Black:
Friis & Jensen(1924)将一组电子放大器中的再生描述为 "回馈 "作用是正的情况，与他们顺便提到的负回馈作用相反。哈罗德•斯蒂芬•布莱克（Harold Stephen Black）在1934年的经典论文中首次详细介绍了负反馈在电子放大器中的应用。根据Black的说法：
Friis 和 Jensen在1924年描述了一种在电子放大器中发生的"回馈 "是正的情况，这一情况与他们顺便提到的负回馈作用相反。到了1934年，Harold Stephen Black在他的经典论文中首次详细介绍了负反馈在电子放大器中的应用。根据Black的说法：
According to Mindell (2002) confusion in the terms arose shortly after this:
According to Mindell (2002) confusion in the terms arose shortly after this:
据Mindell(2002年)说，在这之后不久就出现了术语上的混乱：
据Mindell(2002年)说，术语上的混乱是在这之后不久产生的：
"...Friis and Jensen had made the same distinction Black used between 'positive feed-back' and 'negative feed-back', based not on the sign of the feedback itself but rather on its effect on the amplifier’s gain. In contrast, Nyquist and Bode, when they built on Black’s work, referred to negative feedback as that with the sign reversed. Black had trouble convincing others of the utility of his invention in part because confusion existed over basic matters of definition."
"...Friis and Jensen had made the same distinction Black used between 'positive feed-back' and 'negative feed-back', based not on the sign of the feedback itself but rather on its effect on the amplifier’s gain. In contrast, Nyquist and Bode, when they built on Black’s work, referred to negative feedback as that with the sign reversed. Black had trouble convincing others of the utility of his invention in part because confusion existed over basic matters of definition."
“ ... ... Friis和Jensen对Black在 "正反馈 "和 "负反馈 "之间的区分是一样的，不是基于反馈本身的符号，而是基于它对放大器增益的影响。相反，Nyquist和Bode在Black的工作基础上，将负反馈称为符号相反的反馈。Black难以说服其他人相信他的发明的实用性，部分原因是在基本的定义问题上存在混乱。"
“ ... ... Friis 和 Jensen 对 Black 在 "正反馈 "和 "负反馈 "之间的区分是一样的，不是基于反馈本身的符号，而是基于它对放大器增益的影响。相反，当Nyquist和Bode基于Black的工作基础时，将负反馈称为符号相反的反馈。Black难以说服其他人相信他的发明的实用性，部分原因是在基本的定义问题上存在混乱。"
== Examples and applications ==
== Examples and applications ==
在电子领域
在电子领域
[[File:Regenerartive Receiver-S7300056.JPG|thumb|right|A vintage style regenerative radio receiver. Due to the controlled use of positive feedback, sufficient amplification can be derived from a single [[vacuum tube]] or valve (centre).]]
[[File:Regenerartive Receiver-S7300056.JPG|thumb|right|A vintage style regenerative radio receiver. Due to the controlled use of positive feedback, sufficient amplification can be derived from a single [[vacuum tube]] or valve (centre).|链接=Special:FilePath/Regenerartive_Receiver-S7300056.JPG]]
【图7 A vintage style regenerative radio receiver. Due to the controlled use of positive feedback, sufficient amplification can be derived from a single [[vacuum tube]] or valve (centre). 一个老式的再生无线电接收器。由于使用正反馈的控制，真空管或阀门（中心）就可以产生足够的放大效果。】
[[Regenerative circuit]]s were invented and patented in 1914<ref>{{cite patent |inventor-last=Armstrong |inventor-first=E. H. |country-code=US |patent-number=1113149 |title=Wireless receiving system |date=1914}}</ref> for the amplification and reception of very weak radio signals. Carefully controlled positive feedback around a single [[transistor]] amplifier can multiply its [[Gain (electronics)|gain]] by 1,000 or more.<ref>{{cite web|last=Kitchin|first=Charles|title=A Short Wave Regenerative Receiver Project|url=http://www.electronics-tutorials.com/receivers/regen-radio-receiver.htm|accessdate=23 September 2010|url-status=live|archiveurl=https://web.archive.org/web/20100710100031/http://www.electronics-tutorials.com/receivers/regen-radio-receiver.htm|archivedate=10 July 2010}}</ref> Therefore, a signal can be amplified 20,000 or even 100,000 times in one stage, that would normally have a gain of only 20 to 50. The problem with regenerative amplifiers working at these very high gains is that they easily become unstable and start to oscillate. The radio operator has to be prepared to tweak the amount of feedback fairly continuously for good reception. Modern radio receivers use the [[superheterodyne]] design, with many more amplification stages, but much more stable operation and no positive feedback.
[[Regenerative circuit]]s were invented and patented in 1914<ref>{{cite patent |inventor-last=Armstrong |inventor-first=E. H. |country-code=US |patent-number=1113149 |title=Wireless receiving system |date=1914}}</ref> for the amplification and reception of very weak radio signals. Carefully controlled positive feedback around a single [[transistor]] amplifier can multiply its [[Gain (electronics)|gain]] by 1,000 or more.<ref>{{cite web|last=Kitchin|first=Charles|title=A Short Wave Regenerative Receiver Project|url=http://www.electronics-tutorials.com/receivers/regen-radio-receiver.htm|accessdate=23 September 2010|url-status=live|archiveurl=https://web.archive.org/web/20100710100031/http://www.electronics-tutorials.com/receivers/regen-radio-receiver.htm|archivedate=10 July 2010}}</ref> Therefore, a signal can be amplified 20,000 or even 100,000 times in one stage, that would normally have a gain of only 20 to 50. The problem with regenerative amplifiers working at these very high gains is that they easily become unstable and start to oscillate. The radio operator has to be prepared to tweak the amount of feedback fairly continuously for good reception. Modern radio receivers use the [[superheterodyne]] design, with many more amplification stages, but much more stable operation and no positive feedback.
电子系统中发生热失控的原因是，当电路的某些方面变得更热时，它被允许通过更多的电流，然后它越热，通过的电流就越多，这就使它更热一些，因此它又通过更多的电流。这种影响对有关器件来说通常是灾难性的。如果器件必须在接近其最大功率处理能力的情况下使用，并且在某些条件下可能或可能出现热失控，通常可以通过精心设计来改进。
电子系统中发生热失控的原因是，当电路的某些方面变得更热时，它被允许通过更多的电流，然后它越热，通过的电流就越多，这就使它更热一些，因此它又通过更多的电流。这种影响对有关器件来说通常是灾难性的。如果器件必须在接近其最大功率处理能力的情况下使用，并且在某些条件下可能或可能出现热失控，通常可以通过精心设计来改进。
[[File:Technics SL-1210MK2.jpg|thumb|left|A phonograph turntable is prone to acoustic feedback.]]
[[File:Technics SL-1210MK2.jpg|thumb|left|A phonograph turntable is prone to acoustic feedback.|链接=Special:FilePath/Technics_SL-1210MK2.jpg]]
A phonograph turntable is prone to acoustic feedback.
A phonograph turntable is prone to acoustic feedback.
[[File:Adam Savage HOPE.jpg|thumb|right|220px|[[Video feedback]].]]
[[File:Adam Savage HOPE.jpg|thumb|right|220px|[[Video feedback]].|链接=Special:FilePath/Adam_Savage_HOPE.jpg]]
视频反馈
视频反馈
[[File:Positive Feedback- Childbirth (1).svg|thumb|Positive feedback is the amplification of a body's response to a stimulus. For example, in childbirth, when the head of the fetus pushes up against the cervix (1) it stimulates a nerve impulse from the cervix to the brain (2). When the brain is notified, it signals the pituitary gland to release a hormone called [[oxytocin]](3). Oxytocin is then carried via the bloodstream to the [[uterus]] (4) causing contractions, pushing the fetus towards the cervix eventually inducing childbirth.]]
[[File:Positive Feedback- Childbirth (1).svg|thumb|Positive feedback is the amplification of a body's response to a stimulus. For example, in childbirth, when the head of the fetus pushes up against the cervix (1) it stimulates a nerve impulse from the cervix to the brain (2). When the brain is notified, it signals the pituitary gland to release a hormone called [[oxytocin]](3). Oxytocin is then carried via the bloodstream to the [[uterus]] (4) causing contractions, pushing the fetus towards the cervix eventually inducing childbirth.|链接=Special:FilePath/Positive_Feedback-_Childbirth_(1).svg]]
Positive feedback is the amplification of a body's response to a stimulus. For example, in childbirth, when the head of the fetus pushes up against the cervix (1) it stimulates a nerve impulse from the cervix to the brain (2). When the brain is notified, it signals the pituitary gland to release a hormone called oxytocin(3). Oxytocin is then carried via the bloodstream to the uterus(4) causing contractions, pushing the fetus towards the cervix eventually inducing childbirth.
Positive feedback is the amplification of a body's response to a stimulus. For example, in childbirth, when the head of the fetus pushes up against the cervix (1) it stimulates a nerve impulse from the cervix to the brain (2). When the brain is notified, it signals the pituitary gland to release a hormone called oxytocin(3). Oxytocin is then carried via the bloodstream to the uterus(4) causing contractions, pushing the fetus towards the cervix eventually inducing childbirth.
[[File:Phanerozoic Biodiversity.svg|300px|right|thumb|During the Phanerozoic the [[biodiversity]] shows a steady but not monotonic increase from near zero to several thousands of genera.]]
[[File:Phanerozoic Biodiversity.svg|300px|right|thumb|During the Phanerozoic the [[biodiversity]] shows a steady but not monotonic increase from near zero to several thousands of genera.|链接=Special:FilePath/Phanerozoic_Biodiversity.svg]]
显生宙，生物多样性显示出稳定但不单调的增加，从接近零到几千属。
显生宙，生物多样性显示出稳定但不单调的增加，从接近零到几千属。