Open-loop gain: Difference between revisions

Revision as of 21:53, 15 February 2016

Revision as of 05:04, 1 March 2016

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Open loop gain is usually exceedingly high; in fact, an ideal operational amplifier has infinite open-loop gain. Typically an op-amp may have a maximal open-loop gain of around <math>10^5</math>. Normally, feedback is applied around the op-amp so that the gain of the overall [[electrical network|circuit]] is defined and kept to a figure which is more usable. The very high open-loop gain of the op-amp allows a wide range of feedback levels to be applied to achieve the desired performance.

The open-loop gain of an operational amplifier falls very rapidly with increasing [[frequency]]. Along with [[slew rate]], this is one of the reasons why operational amplifiers have limited [[Bandwidth (signal processing)|bandwidth]].

The definition of open-loop gain (at a fixed frequency) is

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== Role in non-ideal gain ==

The open-loop gain is a physical attribute of an operationoperational amplifier that is often finite in comparison{{Clarify}} to the usual gain, denoted <math>G</math>. While open-loop gain is the gain when there is no feedback in a circuit, an operational amplifier will often be configured to use a feedback configuration such that its gain will be controlled by the feedback circuit components.

Take the case of an inverting operational amplifier configuration. If the resistor between the single output node and the inverting input node is <math>R_2</math> and the resistor between a source voltage and the inverting input node is <math>R_1</math>, then the ideal gain for such a circuit at the output terminal is defined, ideally, to be:

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<math>G = \frac{- \frac{R_2}{R_1}}{1 + \frac{- \frac{R_2}{R_1}}{A}}</math>

Notice that the equation becomes effectiveeffectively the same for the ideal case as <math>A</math> approaches infinity.

In this manner, the open-loop gain is important for computing the actual gain for a given non-ideal operational amplifier network in situations where the ideal model of an operational amplifier begins to become inaccurate.

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== See also ==

* [[Loop gain]] (includes both the open-loop gain and the feedback attenuation)

* [[Loop gain]]

{{DEFAULTSORT:Open-Loop Gain}}