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Slew rate

In electronics and electromagnetics, slew rate is defined as the change of voltage or current, or any other electrical or electromagnetic quantity, per unit of time. Expressed in SI units, the unit of measurement is given as the change per second, but in the context of electronic circuits a slew rate is usually expressed in terms of microseconds (μs) or nanoseconds (ns).

slew rate effect on a square wave: red=desired output, green=actual output

Electronic circuits may specify minimum or maximum limits on the slew rates for their inputs or outputs, with these limits only valid under some set of given conditions (e.g. output loading). When given for the output of a circuit, such as an amplifier, the slew rate specification guarantees that the speed of the output signal transition will be at least the given minimum, or at most the given maximum. When applied to the input of a circuit, it instead indicates that the external driving circuitry needs to meet those limits in order to guarantee the correct operation of the receiving device. If these limits are violated, some error might occur and correct operation is no longer guaranteed.

For example, when the input to a digital circuit is driven too slowly, the digital input value registered by the circuit may oscillate between 0 and 1 during the signal transition.[1] In other cases, a maximum slew rate is specified[2] in order to limit the high frequency content present in the signal, thereby preventing such undesirable effects as ringing or radiated interference.[3]

In amplifiers, limitations in slew rate capability can give rise to non-linear effects. For a sinusoidal waveform not to be subject to slew rate limitation, the slew rate capability (in volts per second) at all points in an amplifier must satisfy the following condition:

where f is the operating frequency, and is the peak amplitude of the waveform, i.e. half the peak-to-peak swing of a sinusoid.

In mechanics the slew rate is the change in position over time of an object which orbits around the observer, measured in radians, degrees or turns per unit of time. It has dimension

Definition Edit

The slew rate of an electronic circuit is defined as the rate of change of the voltage per unit time. Slew rate is usually expressed in units of V/μs.[4]

 

where   is the output produced by the amplifier as a function of time t.

Measurement Edit

The slew rate can be measured using a function generator (usually square wave) and an oscilloscope (CRO). The slew rate is the same, regardless of whether feedback is considered.

Slew rate limiting in amplifiers Edit

There are slight differences between different amplifier designs in how the slewing phenomenon occurs. However, the general principles are the same as in this illustration.

The input stage of modern amplifiers is usually a differential amplifier with a transconductance characteristic. This means the input stage takes a differential input voltage and produces an output current into the second stage.

The transconductance is typically very high — this is where the large open loop gain of the amplifier is generated. This also means that a fairly small input voltage can cause the input stage to saturate. In saturation, the stage produces a nearly constant output current.

The second stage of modern power amplifiers is, among other things, where frequency compensation is accomplished. The low pass characteristic of this stage approximates an integrator. A constant current input will therefore produce a linearly increasing output. If the second stage has an effective input capacitance   and voltage gain  , then slew rate in this example can be expressed as:

 

where   is the output current of the first stage in saturation.

Slew rate helps us identify the maximum input frequency and amplitude applicable to the amplifier such that the output is not significantly distorted. Thus it becomes imperative to check the datasheet for the device's slew rate before using it for high-frequency applications.

Musical applications Edit

In electronic musical instruments, slew circuitry or software-generated slew functions are used deliberately to provide a portamento (also called glide or lag) feature, where an initial digital value or analog control voltage is slowly transitioned to a new value over a period of time (see interpolation).

See also Edit

References Edit

  1. ^ http://www.microsemi.com/document-portal/doc_view/130021-ac161-using-schmitt-triggers-for-low-slew-rate-input-app-note[bare URL PDF]
  2. ^ http://www.nxp.com/documents/user_manual/UM10204.pdf 2013-05-11 at the Wayback Machine revision 6, pg 48: the Fast-mode and Fast-mode Plus minimum rise/fall times effectively become a maximum slew rate limit.
  3. ^ "Edge rate control improves performance in modern high-speed circuits". 4 July 2000.
  4. ^ "Slew Rate: What is it?". Electrical4U.

External links Edit

  • Linear Circuit Design Chapter 1: Op Amps

slew, rate, other, uses, slew, disambiguation, this, article, needs, additional, citations, verification, please, help, improve, this, article, adding, citations, reliable, sources, unsourced, material, challenged, removed, find, sources, news, newspapers, boo. For other uses see Slew disambiguation This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Slew rate news newspapers books scholar JSTOR March 2016 Learn how and when to remove this template message In electronics and electromagnetics slew rate is defined as the change of voltage or current or any other electrical or electromagnetic quantity per unit of time Expressed in SI units the unit of measurement is given as the change per second but in the context of electronic circuits a slew rate is usually expressed in terms of microseconds ms or nanoseconds ns slew rate effect on a square wave red desired output green actual outputElectronic circuits may specify minimum or maximum limits on the slew rates for their inputs or outputs with these limits only valid under some set of given conditions e g output loading When given for the output of a circuit such as an amplifier the slew rate specification guarantees that the speed of the output signal transition will be at least the given minimum or at most the given maximum When applied to the input of a circuit it instead indicates that the external driving circuitry needs to meet those limits in order to guarantee the correct operation of the receiving device If these limits are violated some error might occur and correct operation is no longer guaranteed For example when the input to a digital circuit is driven too slowly the digital input value registered by the circuit may oscillate between 0 and 1 during the signal transition 1 In other cases a maximum slew rate is specified 2 in order to limit the high frequency content present in the signal thereby preventing such undesirable effects as ringing or radiated interference 3 In amplifiers limitations in slew rate capability can give rise to non linear effects For a sinusoidal waveform not to be subject to slew rate limitation the slew rate capability in volts per second at all points in an amplifier must satisfy the following condition S R 2 p f V p k displaystyle mathrm SR geq 2 pi fV mathrm pk where f is the operating frequency and V p k displaystyle V mathrm pk is the peak amplitude of the waveform i e half the peak to peak swing of a sinusoid In mechanics the slew rate is the change in position over time of an object which orbits around the observer measured in radians degrees or turns per unit of time It has dimension T 1 displaystyle mathsf T 1 Contents 1 Definition 2 Measurement 3 Slew rate limiting in amplifiers 4 Musical applications 5 See also 6 References 7 External linksDefinition EditThe slew rate of an electronic circuit is defined as the rate of change of the voltage per unit time Slew rate is usually expressed in units of V ms 4 S R max d v o u t t d t displaystyle mathrm SR max left frac dv mathrm out t dt right nbsp where v o u t t displaystyle v mathrm out t nbsp is the output produced by the amplifier as a function of time t Measurement EditThe slew rate can be measured using a function generator usually square wave and an oscilloscope CRO The slew rate is the same regardless of whether feedback is considered Slew rate limiting in amplifiers EditThere are slight differences between different amplifier designs in how the slewing phenomenon occurs However the general principles are the same as in this illustration The input stage of modern amplifiers is usually a differential amplifier with a transconductance characteristic This means the input stage takes a differential input voltage and produces an output current into the second stage The transconductance is typically very high this is where the large open loop gain of the amplifier is generated This also means that a fairly small input voltage can cause the input stage to saturate In saturation the stage produces a nearly constant output current The second stage of modern power amplifiers is among other things where frequency compensation is accomplished The low pass characteristic of this stage approximates an integrator A constant current input will therefore produce a linearly increasing output If the second stage has an effective input capacitance C displaystyle C nbsp and voltage gain A 2 displaystyle A 2 nbsp then slew rate in this example can be expressed as S R I s a t C A 2 displaystyle mathrm SR frac I mathrm sat C A 2 nbsp where I s a t displaystyle I mathrm sat nbsp is the output current of the first stage in saturation Slew rate helps us identify the maximum input frequency and amplitude applicable to the amplifier such that the output is not significantly distorted Thus it becomes imperative to check the datasheet for the device s slew rate before using it for high frequency applications Musical applications EditIn electronic musical instruments slew circuitry or software generated slew functions are used deliberately to provide a portamento also called glide or lag feature where an initial digital value or analog control voltage is slowly transitioned to a new value over a period of time see interpolation See also EditPower bandwidthReferences Edit http www microsemi com document portal doc view 130021 ac161 using schmitt triggers for low slew rate input app note bare URL PDF http www nxp com documents user manual UM10204 pdf Archived 2013 05 11 at the Wayback Machine revision 6 pg 48 the Fast mode and Fast mode Plus minimum rise fall times effectively become a maximum slew rate limit Edge rate control improves performance in modern high speed circuits 4 July 2000 Slew Rate What is it Electrical4U External links EditSlew rate explanation with interactive example and detailed calculation for a standard opamp circuit Linear Circuit Design Chapter 1 Op Amps Retrieved from https en wikipedia org w index php title Slew rate amp oldid 1179455105, wikipedia, wiki, book, books, library,

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