Op-amp Tutorial Includes:
運算放大器教程包括：
Introduction     Op amp gain     Bandwidth     Op amp slew rate     Offset null     Input impedance     Output impedance     Current feedback op amp     Understanding specifications     How to choose an op amp     Op amp circuits summary
簡介 運算放大器增益 頻寬 運算放大器轉換速率 偏移零 輸入阻抗 輸出阻抗 電流反饋運算放大器 瞭解規格 如何選擇運算放大器 運算放大器電路總結    

The output of an operational amplifier can only change by a certain amount in a given time: this limit is called the slew rate of the op-amp.
運算放大器的輸出在給定時間內只能變化一定量：這個限制稱為運算放大器的轉換速率。

Although slew rate is not always mentioned when undertaking an electronic circuit design, it can be a critical factor in ensuring that an amplifier is able to provide an output that is a faithful representation of the input..
儘管在進行電子電路設計時並不總是提到轉換速率，但它可能是確保放大器能夠提供真實表示輸入的輸出的關鍵因素。

Operational amplifier slew rate can limit the performance of a circuit if the slew rate requirement is exceeded. It can distort the waveform and prevent the input signal being faithfully represented at the output if the slew rate is exceeded.
如果超過轉換速率要求，運算放大器轉換速率會限制電路的性能。如果超過轉換速率，它會使波形失真並阻止輸入信號在輸出端忠實表示。

One of the figures quoted in the data sheets for operational amplifiers is the slew rate, and this needs to be checked and some calculations made to ensure that the particular op amp device can handle the output change rate demanded of it.
運算放大器數據資料中引用的數位之一是轉換速率，需要對此進行檢查並進行一些計算，以確保特定的運算放大器器件能夠處理所需的輸出變化率。

In certain applications where speed is required and the output needs to change quickly, the slew rate of the operational amplifier can have a significant effect on the overall performance of the electronic circuit, and the design needs to accommodate this.
在某些需要速度和輸出需要快速變化的應用中，運算放大器的轉換速率會對電子電路的整體性能產生重大影響，設計需要適應這一點。

Op amp slew rate basics
運算放大器轉換速率基礎知識

The slew rate of an op amp or any amplifier circuit is the rate of change in the output voltage caused by a step change on the input.
運算放大器或任何放大器電路的轉換速率是由輸入的階躍變化引起的輸出電壓變化率。

It is measured as a voltage change in a given time - typically V / µs or V / ms.
它以給定時間內的電壓變化來測量 - 通常為 V / μs 或 V / ms。

A typical general purpose device may have a slew rate of 10 V / microsecond. This means that when a large step change is placed on the input, the electronic device would be able to provide an output 10 volt change in one microsecond.
典型的通用器件的轉換速率可能為 10 V/微秒。這意味著，當輸入端發生較大的階躍變化時，電子設備將能夠在一微秒內提供 10 伏特的輸出變化。

The figures for slew rate change are dependent upon the type of operational amplifier being used. Low power op-amps may only have figures of a volt per microsecond, whereas there are fast operational amplifiers capable to providing rates of 1000 V / µsecond.
轉換速率變化的數字取決於所使用的運算放大器的類型。低功率運算放大器可能只有每微秒一伏特的數位，而快速運算放大器能夠提供 1000 V/μsecond 的速率。

The slew rate is governed by the operational amplifier itself and as a result the slew rate performance of the whole electronic circuit design is not affected by the feedback applied.
轉換速率由運算放大器本身控制，因此整個電子電路設計的轉換速率性能不受施加的反饋的影響。

The chief causes for the slew rate limitations are caused by the internal frequency compensation included in most operational amplifiers to provide stability, especially at high frequencies.
轉換速率限制的主要原因是大多數運算放大器中包含的內部頻率補償，以提供穩定性，尤其是在高頻下。

Another contributory factor is the small internal drive currents, as well as any limitations int he output stage. These all combine together to limit the rate at which the output can change from one level to another.
另一個影響因素是較小的內部驅動電流，以及輸出級中的任何限制。這些都結合在一起，以限制輸出從一個級別變為另一個級別的速率。

Op amps may have different slew rates for positive and negative going transitions because of the circuit configuration.
由於電路配置的原因，運算放大器的正向和負向轉換可能具有不同的轉換速率。

Op amps have a complementary output to pull the signal up and down and this means the two sides of the circuit cannot be exactly the same. However it is often assumed that they have reasonably symmetrical performance levels.
運算放大器具有互補輸出，用於上下拉動信號，這意味著電路的兩側不可能完全相同。但是，通常假設它們具有相當對稱的性能水準。

There are still some operational amplifiers that are not internally compensated and need external electronic components to provide the compensation.
還有一些運算放大器沒有內部補償，需要外部電子元件來提供補償。

These can be optimised to provide the best balance between stability and slew rate. In this way the best overall performance can be obtained.
這些可以進行優化，以提供穩定性和轉換速率之間的最佳平衡。通過這種方式，可以獲得最佳的整體性能。

Slew rate rationale  轉換速率基本原理

The slew rate issues arise from the internal circuitry within the op amp. There are various reasons for the limitations of most chips:
轉換速率問題由運算放大器內部電路引起。大多數晶元的局限性有多種原因：

• Frequency compensation:   The capacitors used within the chip to reduce the high frequency response have a marked effect on the slew rate. Limiting the frequency response also limits the rate of change that can occur at the output, and hence it affects the overall op amp slew rate. However to ensure that operational amplifiers remain stable the frequency compensation components are always included, and the resulting effect on slew rate needs too be accommodated in the overall circuit design.
  頻率補償：晶元內部用於降低高頻回應的電容器對轉換速率有顯著影響。限制頻率回應也會限制輸出端可能發生的變化率，因此會影響整體運算放大器轉換速率。然而，為了確保運算放大器保持穩定，頻率補償元件始終包含在內，並且對轉換速率的影響也需要在整個電路設計中考慮。

• Output driver limitations:   Within the chip, and particularly within the output driver, the low current levels limit the rate at which change can occur. This limits the slew rate of the op amp. It is found that this is the area of the performance where rise and fall slew rates may be different.
  輸出驅動器限制：在晶元內部，特別是在輸出驅動器內部，低電流水準限制了變化的速率。這限制了運算放大器的 slew rate。發現這是 Rising 和 Fall Slew Rate 可能不同的性能區域。

  This results from the different ways that the chip increases and decreases the output voltage. For example the output may employ a form of complementary output stage. The slightly different characteristics of each half will cause a small amount on difference between the rise and fall slew rate capabilities.
  這是由於 chip 增加和減少 output voltage 的方式不同造成的。例如，output 可以採用一種互補輸出級的形式。每半部分的特性略有不同，將導致上升和下降轉換速率能力之間存在少量差異。

• High gain input stages:   Operational amplifiers use high gain differential input stages. The high gain, and the fact that they are transconductance amplifiers where a voltage input produces a current output means that there is a possibility that the signals can saturate causing the amplifier to act as a constant current source. When this happens the output change rate of the amplifier is severely limited.
  高增益輸入級：運算放大器使用高增益差分輸入級。高增益以及它們是跨導放大器的事實，其中電壓輸入產生電流輸出，這意味著信號有可能飽和，導致放大器充當恆流源。發生這種情況時，放大器的輸出變化率會受到嚴重限制。

It can be seen that the slew rate tends to be governed by factors within the operational amplifier chip itself. Accordingly it is necessary to select a chip for the electronic circuit design that can provide the slew rate that is needed. Calculation of the required slew rate for a given circuit scenario means that any issues can be addressed at the deign stage of the circuit rather than discovering a problem later.
可以看出，轉換速率往往受運算放大器晶元本身內部因素的控制。因此，有必要為電子電路設計選擇一個可以提供所需轉換速率的晶元。計算給定電路場景所需的轉換速率意味著任何問題都可以在電路的設計階段解決，而不是在以後發現問題。

Slew rate distortion  轉換速率失真

If an op amp is operated above its slew rate limit, signals will become distorted. The easiest way to see this is to look at the example of a sine wave.
如果運算放大器的工作頻率高於其轉換速率限制，信號將變得失真。看清這一點的最簡單方法是看正弦波的例子。

The maximum rate of voltage change occurs at the zero crossing point.
電壓變化的最大速率發生在過零點。

It is possible to find the maximum frequency or voltage that can be accommodated. A sine wave with a frequency of f Hertz and peak voltage V volts requires an operational amplifier with a slew rate of 2 x Π x f x V volts per second. This is required to ensure the maximum slew rate requirement which occurs at the zero crossing point can be met.
可以找到可以容納的最大頻率或電壓。頻率為 f 赫茲且峰值電壓為 V 伏特的正弦波需要一個轉換速率為每秒 2 x Π x f x V 伏特的運算放大器。這是為了確保滿足過零點出現的最大轉換速率要求。

As can be seen in the diagram, in the limit, the op amp slewing distortion will result in the creation of a triangular waveform. If the frequency is increased the op amp will be even less able to keep up and therefore the amplitude of the output waveform will decrease.
從圖中可以看出，在極限中， op amplifier slewing distortion 將導致產生三角波形。如果頻率增加，運算放大器將更無法跟上，因此輸出波形的幅度將減小。

The slew rate may also not be linear over the whole range. As a result the waveform may exhibit a faster rise for the first part of the change, then reverting to the more expected slew rate.
轉換速率在整個範圍內也可能不是線性的。因此， waveform 可能會在更改的第一部分表現出更快的 Rising ，然後恢復到更預期的 slew rate。

Also note that slew rate is normally specified for a circuit acting as a voltage follower with unity gain and with a full swing step input. This means that there is a large differential drive and as a result large amounts of current flow. For different configurations where there is a small input voltage and larger gain, the slew rate will be much less.
另請注意，轉換速率通常是為充當電壓跟隨器的電路指定的，具有單位增益和全擺幅步長輸入。這意味著存在較大的差分驅動器，因此會產生大量的電流。對於輸入電壓較小而增益較大的不同配置，轉換速率將要小得多。

Slew rate calculation & formula
轉換速率計算和公式

It is relatively easy to calculate the slew rate of an amplifier that is required for a given application or electronic circuit design from a knowledge of the maximum voltage and frequency required.
根據所需的最大電壓和頻率知識，計算給定應用或電子電路設計所需的放大器的轉換速率相對容易。

To give distortion free operation, the slew rate of the amplifier, the simple formula below can be used.
為了實現無失真作，可以使用以下簡單公式的放大器的轉換速率。

Where  哪裡
    slew rate is measured in volts / second, although actual measurements are often given in v/µs
轉換速率以 Volts/s 為單位，但實際測量值通常以 V/μs 為單位
    f = the highest signal frequency, Hz
f = 最高信號頻率 Hz
    V = the maximum peak voltage of the signal.
V = 信號的最大峰值電壓。

As an example, take the scenario where an op amp is required to amplify a signal with a peak amplitude of 5 volts at a frequency of 25kHz. An op amp with a slew rate of at least 2 π x 25 000 x 5 = 0.785V/µs would be required.
例如，需要一個運算放大器來放大峰值幅度為 5 V、頻率為 25kHz 的信號。需要一個轉換速率至少為 2 π x 25 000 x 5 = 0.785V/μs 的運算放大器。

Slew rate calculator  轉換速率計算機

While it is possible to manually calculate the slew rate required for an op-amp or other amplifier manually, the simple op-amp slew rate calculator below provides a much easier and faster option.
雖然可以手動計算運算放大器或其他放大器所需的轉換速率，但下面的簡單運算放大器轉換速率計算機提供了一個更簡單、更快速的選擇。

Op amp slew rate may not affect some electronic circuit designs, but for others it may introduce significant levels of distortion. Accordingly it is always best to check that the slew rate limits for the chip will not be exceeded and opt for another device if this is likely for any electronic circuit being designed. There are many high slew rate devices on the market and these can normally be dropped into the circuit in place of a slower device with little modification to the rest of the circuit.
運算放大器轉換速率可能不會影響某些電子電路設計，但對於其他設計，它可能會引入顯著的失真。因此，最好檢查晶元的轉換速率限制是否不超過，如果這可能適用於正在設計的任何電子電路，則選擇其他器件。市場上有許多高轉換速率器件，這些器件通常可以放入電路中，以代替較慢的器件，而無需對電路的其餘部分進行少量修改。

By addressing the op amp slew rate issues at the initial electronic circuit design concept stages, it is possible to ensure that it is not an issues under the circuit conditions that are anticipated to be encountered.
通過在初始電子電路設計概念階段解決運算放大器轉換速率問題，可以確保在預期會遇到的電路條件下不會遇到問題。

  Written by Ian Poole .
作者 Ian Poole .
  Experienced electronics engineer and author.
經驗豐富的電子工程師和作家。

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