About: Phase margin     Goto   Sponge   NotDistinct   Permalink

An Entity of Type : yago:WikicatElectronicAmplifiers, within Data Space : dbpedia.org associated with source document(s)

In electronic amplifiers, the phase margin (PM) is the difference between the phase and 180°, for an amplifier's output signal (relative to its input), at a certain frequency. . Typically the open-loop phase lag (relative to input) varies with frequency, progressively increasing to exceed 180°, at which frequency the output signal becomes inverted, or antiphase in relation to the input. The PM will be positive but decreasing at frequencies less than the frequency at which inversion sets in (at which PM = 0), and PM is negative (PM < 0) at higher frequencies. In the presence of negative feedback, a zero or negative PM at a frequency where the loop gain exceeds unity (1) guarantees instability. Thus positive PM is a "safety margin" that ensures proper (non-oscillatory) operation of the circu

AttributesValues
rdf:type
rdfs:label
  • Phase margin
  • Zapas stabilności
  • 相位裕度
rdfs:comment
  • In electronic amplifiers, the phase margin (PM) is the difference between the phase and 180°, for an amplifier's output signal (relative to its input), at a certain frequency. . Typically the open-loop phase lag (relative to input) varies with frequency, progressively increasing to exceed 180°, at which frequency the output signal becomes inverted, or antiphase in relation to the input. The PM will be positive but decreasing at frequencies less than the frequency at which inversion sets in (at which PM = 0), and PM is negative (PM < 0) at higher frequencies. In the presence of negative feedback, a zero or negative PM at a frequency where the loop gain exceeds unity (1) guarantees instability. Thus positive PM is a "safety margin" that ensures proper (non-oscillatory) operation of the circu
  • Zapas stabilności określa praktyczną przydatność zamkniętego układu automatycznej regulacji. Jest miarą odległości danego punktu pracy urządzenia lub algorytmu od granicy stabilności, określanej przez dowolne z kryterium stabilności układu automatycznej regulacji. Dla zamkniętych układów regulacji zapas stabilności definiuje się, na podstawie charakterystyk układu otwartego, jako parę liczb, z których pierwsza określa zapas amplitudy (nazywany również zapasem modułu), a druga – zapas fazy.
  • 在电子放大器中,相位裕度(PM)是放大器的输出信号(相对于其输入)的相位与180°之间的差(单位为度),对频率的函数。通常开环相位延迟(相对于输入)随频率变化,逐步增加到超过180°,此频率下输出信号(相对于输入)反相。PM为正值,但会随着频率下降,在截止频率(PM = 0)反相,于是在高频率PM为负值(PM < 0)。在存在负反馈时,环路增益超过1情况下PM频率为零或负值可以保证系统不稳定。因此PM为正是能保证该电路正常工作(不振荡)的“安全裕度”。这不仅适用于放大器电路,同样适用于不同负载条件(如无功负载)下的有源滤波器。在最简单的形式中,涉及有非抗性反馈的理想负反馈电压放大器,在放大器的开环电压增益等于所需闭环直流电压增益时测定相位裕度。 更一般地,PM是由放大器及其反馈网络结合在一起(通常在放大器输入处开环)定义的,在环路增益为1的频率测定,并在闭合回路之前,通过尝试输入源的开环输出的方式,将其从中去除。 在上述环路增益定义中,假设放大器输入呈现零负载。要在零负载输入下工作,为了确定该环路增益的频率响应,反馈网络的输出需要加一个等效负载。 假定增益对频率的图象以一个负斜率穿过单位增益仅一次。只有在抗性或有源反馈网络(如有源滤波器的情形)才需要这么考虑。 另一個相關的度量是增益裕度。增益裕度是以相位為裕度是-180度時的增益為準進行計算。
sameAs
dct:subject
Wikipage page ID
Wikipage revision ID
Link from a Wikipage to another Wikipage
Link from a Wikipage to an external page
foaf:isPrimaryTopicOf
prov:wasDerivedFrom
has abstract
  • In electronic amplifiers, the phase margin (PM) is the difference between the phase and 180°, for an amplifier's output signal (relative to its input), at a certain frequency. . Typically the open-loop phase lag (relative to input) varies with frequency, progressively increasing to exceed 180°, at which frequency the output signal becomes inverted, or antiphase in relation to the input. The PM will be positive but decreasing at frequencies less than the frequency at which inversion sets in (at which PM = 0), and PM is negative (PM < 0) at higher frequencies. In the presence of negative feedback, a zero or negative PM at a frequency where the loop gain exceeds unity (1) guarantees instability. Thus positive PM is a "safety margin" that ensures proper (non-oscillatory) operation of the circuit. This applies to amplifier circuits as well as more generally, to active filters, under various load conditions (e.g. reactive loads). In its simplest form, involving ideal negative feedback voltage amplifiers with non-reactive feedback, the phase margin is measured at the frequency where the open-loop voltage gain of the amplifier equals the desired closed-loop DC voltage gain. More generally, PM is defined as that of the amplifier and its feedback network combined (the "loop", normally opened at the amplifier input), measured at a frequency where the loop gain is unity, and prior to the closing of the loop, through tying the output of the open loop to the input source, in such a way as to subtract from it. In the above loop-gain definition, it is assumed that the amplifier input presents zero load. To make this work for non-zero-load input, the output of the feedback network needs to be loaded with an equivalent load for the purpose of determining the frequency response of the loop gain. It is also assumed that the graph of gain vs. frequency crosses unity gain with a negative slope and does so only once. This consideration matters only with reactive and active feedback networks, as may be the case with active filters. Phase margin and its important companion concept, gain margin, are measures of stability in closed-loop, dynamic-control systems. Phase margin indicates relative stability, the tendency to oscillate during its damped response to an input change such as a step function. Gain margin indicates absolute stability and the degree to which the system will oscillate, without limit, given any disturbance. The output signals of all amplifiers exhibit a time delay when compared to their input signals. This delay causes a phase difference between the amplifier's input and output signals. If there are enough stages in the amplifier, at some frequency, the output signal will lag behind the input signal by one cycle period at that frequency. In this situation, the amplifier's output signal will be in phase with its input signal though lagging behind it by 360°, i.e., the output will have a phase angle of −360°. This lag is of great consequence in amplifiers that use feedback. The reason: the amplifier will oscillate if the fed-back output signal is in phase with the input signal at the frequency at which its open-loop voltage gain equals its closed-loop voltage gain and the open-loop voltage gain is one or greater. The oscillation will occur because the fed-back output signal will then reinforce the input signal at that frequency. In conventional operational amplifiers, the critical output phase angle is −180° because the output is fed back to the input through an inverting input which adds an additional −180°. In practice, feedback amplifiers must be designed with phase margins substantially in excess of 0°, even though amplifiers with phase margins of, say, 1° are theoretically stable. The reason is that many practical factors can reduce the phase margin below the theoretical minimum. A prime example is when the amplifier's output is connected to a capacitive load. Therefore, operational amplifiers are usually compensated to achieve a minimum phase margin of 45° or so. This means that at the frequency at which the open and closed loop gains meet, the phase angle is −135°. The calculation is: -135° - (-180°) = 45°. See Warwickor Stoutfor a detailed analysis of the techniques and results of compensation to insure adequate phase margins. See also the article "Pole splitting". Often amplifiers are designed to achieve a typical phase margin of 60 degrees. If the typical phase margin is around 60 degrees then the minimum phase margin will typically be greater than 45 degrees. A phase margin of 60 degrees is also a magic number because it allows for the fastest settling time when attempting to follow a voltage step input (a Butterworth design). An amplifier with lower phase margin will ring for longer and an amplifier with more phase margin will take a longer time to rise to the voltage step's final level. A related measure is gain margin. While phase margin comes from the phase where the loop gain equals one, the gain margin is based upon the gain where the phase equals -180 degrees.
  • Zapas stabilności określa praktyczną przydatność zamkniętego układu automatycznej regulacji. Jest miarą odległości danego punktu pracy urządzenia lub algorytmu od granicy stabilności, określanej przez dowolne z kryterium stabilności układu automatycznej regulacji. Dla zamkniętych układów regulacji zapas stabilności definiuje się, na podstawie charakterystyk układu otwartego, jako parę liczb, z których pierwsza określa zapas amplitudy (nazywany również zapasem modułu), a druga – zapas fazy. W praktyce zapas stabilności powinien być wystarczająco duży, np. większy niż 6 decybeli i 30 stopni lub 8 decybeli i 45 stopni.
  • 在电子放大器中,相位裕度(PM)是放大器的输出信号(相对于其输入)的相位与180°之间的差(单位为度),对频率的函数。通常开环相位延迟(相对于输入)随频率变化,逐步增加到超过180°,此频率下输出信号(相对于输入)反相。PM为正值,但会随着频率下降,在截止频率(PM = 0)反相,于是在高频率PM为负值(PM < 0)。在存在负反馈时,环路增益超过1情况下PM频率为零或负值可以保证系统不稳定。因此PM为正是能保证该电路正常工作(不振荡)的“安全裕度”。这不仅适用于放大器电路,同样适用于不同负载条件(如无功负载)下的有源滤波器。在最简单的形式中,涉及有非抗性反馈的理想负反馈电压放大器,在放大器的开环电压增益等于所需闭环直流电压增益时测定相位裕度。 更一般地,PM是由放大器及其反馈网络结合在一起(通常在放大器输入处开环)定义的,在环路增益为1的频率测定,并在闭合回路之前,通过尝试输入源的开环输出的方式,将其从中去除。 在上述环路增益定义中,假设放大器输入呈现零负载。要在零负载输入下工作,为了确定该环路增益的频率响应,反馈网络的输出需要加一个等效负载。 假定增益对频率的图象以一个负斜率穿过单位增益仅一次。只有在抗性或有源反馈网络(如有源滤波器的情形)才需要这么考虑。 相位裕度及其相关重要概念波德圖,是闭环动态控制系统稳定性的量度。相位裕度能够表现相对稳定性(其对于阶跃函数等输入变化的阻尼响应振荡的倾向)。增益裕度能够表现绝对稳定性和给定任意干扰,不加限制,系统会振荡的程度。 所有的放大器的输出信号相比其输入信号都呈现出时间延迟。此延迟会引起放大器的输入和输出信号之间的相位差。如果放大器的级数足够多,某一频率下的输出信号就会比输入信号滞后一个周期。在此情况下,放大器的输出信号的相位会与其输入信号的相位相同,虽然滞后了360°,也就是说输出的相位角为−360°。这个延迟对使用反馈的放大器有很大影响。原因是:若输出信号反馈的相位处于与放大器的开环电压增益等于其闭环电压增益的频率且开环电压增益为1或更大,则放大器会振荡。出现振荡的原因是输出信号反馈会在该频率加强输入信号。 在常规运算放大器中,临界输出相位角为−180°,因为输出是通过−180°的反相输入反馈到输入的。 在实际设计中,反馈放大器的相位裕度超出0°许多,尽管相位裕度为1°的放大器理论上就是稳定的了。原因在于许多实际因素会将相位裕度减小到低于理论最小值。最好的例子就是放大器的输出连到一个容性负载上。因此,运算放大器通常要补偿到最小相位裕度为45°左右。这一意味着处于开环与闭环增益相同的频率时相位裕度为−135°。计算为:-135° - (-180°) = 45°. 为确保足够的相位裕度所做的补偿的方法和结果的详细分析参见Warwick或者Stout。另请参阅条目“极点分离”。通常放大器都会设计成典型相位裕度为60度。如果典型相位裕度在60度附近,那么最小相位裕度就会大于45度。相位裕度为60度也是一个神奇的数字,因为当试图跟随电压阶跃输入(巴特沃斯滤波器设计)时,调节时间最短。相位裕度小的放大器会振铃较长时间,而相位裕度更大的放大器上升到电压阶跃的最终水平所花时间就会较长。 另一個相關的度量是增益裕度。增益裕度是以相位為裕度是-180度時的增益為準進行計算。
http://purl.org/voc/vrank#hasRank
http://purl.org/li...ics/gold/hypernym
is rdfs:seeAlso of
is Link from a Wikipage to another Wikipage of
is foaf:primaryTopic of
Faceted Search & Find service v1.17_git39 as of Aug 09 2019


Alternative Linked Data Documents: PivotViewer | iSPARQL | ODE     Content Formats:       RDF       ODATA       Microdata      About   
This material is Open Knowledge   W3C Semantic Web Technology [RDF Data] Valid XHTML + RDFa
OpenLink Virtuoso version 07.20.3232 as of Aug 9 2019, on Linux (x86_64-generic-linux-glibc25), Single-Server Edition (61 GB total memory)
Data on this page belongs to its respective rights holders.
Virtuoso Faceted Browser Copyright © 2009-2019 OpenLink Software