Operational Amplifier 

By on

The fundamental component of any analogue computer is the operational amplifier, or op amp. An operational amplifier (often called an op-amp,) is a high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output.

Op-amps are among the most widely used electronic devices today, being used in a vast array of consumer, industrial, and scientific devices. Many standard IC op-amps cost only a few cents in moderate production volume; however some integrated or hybrid operational amplifiers with special performance specifications may cost significantly more.

Operation

Basic Op Amp CircuitThe amplifier's differential inputs consist of a V+ input and a V input, and ideally the op amp amplifies only the difference in [[voltage]] between the two (called the differential input voltage). The output voltage of the op-amp is given by the equation:

myElectrical Equation 

where V+ is the voltage at the non-inverting terminal, V- is the voltage at the inverting terminal and AOL is the open-loop gain of the amplifier.

The magnitude of AOL is typically very large (seldom less than a million) and even a quite small differential input voltage will result in amplifier saturation.

If linear operation is desired, negative feedback must be used and is usually achieved by applying a portion of the output voltage to the inverting input. The feedback enables the output of the amplifier to keep the inputs at or near the same voltage so that saturation does not occur.

Idea Op Amp

An ideal op-amp is would have the following properties. In practice, none of these ideals can be realized, and various shortcomings and compromises have to be accepted.

  • Infinite open-loop gain
  • Infinite voltage range available at the output
  • Infinite bandwidth
  • Infinite input impedance
  • Zero input current
  • Zero input offset voltage
  • Infinite slew rate
  • Zero output impedance
  • Zero noise
  • Infinite common-mode rejection ratio (CMRR)
  • Infinite power supply rejection ratio

Applications

Op-amps are often used in electronic circuit design. The use of op-amps as circuit blocks is generally much easier and clearer than specifying all their individual circuit elements ([[transistors]],[[resistor| resistors]], etc.).

Basic Op 'Amp' Circuits

 

Circuit Transfer Function
Inverting amplifier
myElectrical Equation
Non-inverting amplifier
myElectrical Equation
Differential input amplifier

myElectrical Equation

with

myElectrical Equation

Adding, Subtracting & Scaling
myElectrical Equation
Voltage follower
myElectrical Equation
Current amplifier

myElectrical Equation
Integrating amplifier
myElectrical Equation
Differentiating amplifier

myElectrical Equation

 

Voltage Gain of Op-amps

Op Amp Gain
Op-amp Gain

Real op-amp such as the commonly available uA741, do not have infinite gain or bandwidth but have a typical "Open Loop Gain". This is defined as the amplifiers output amplification without any external feedback signals connected to it and for a typical operational amplifier is 105 to 106 at DC (zero Hz). This output gain decreases linearly with frequency down to "Unity Gain" or 1, at about 1MHz.



Steven McFadyen's avatar Steven McFadyen

Steven has over twenty five years experience working on some of the largest construction projects. He has a deep technical understanding of electrical engineering and is keen to share this knowledge. About the author

myElectrical Engineering

comments powered by Disqus

  1. on ap's avatar on ap says:
    10/26/2013 4:59 PM

    I like this page so much. All imformation here help for my work


Comments are closed for this post:
  • have a question or need help, please use our Questions Section
  • spotted an error or have additional info that you think should be in this post, feel free to Contact Us



Induction Motor Equivalent Circuit

Induction motors are frequently used in both industrial and domestic applications.  Within the induction motor, an electrical current in the rotor is induced...

Contribute to myElectrcial

Have an opinion or something to say, want to ask or answer questions, share your knowledge then use our site to do it . As a community of people interested...

Lithium Ion Battery

Over recent years the Lithium Ion battery has become popular in applications requiring high power densities with small weight and footprint.  Today Lithium...

IEC Document Designation

Often document control is dictated by project requirements, for example a particular organisation may have an existing numbering system. Existing company...

Lightning Risk Assessment (IEC 62305)

IEC 62305 'Protection against lightning' requires a risk assessment be carried out to determine the characteristics of any lightning protection system...

Smarter Electrical Distribution

The other day I came across an article in Technology Review on the development of a smart transformer. A professor at North Carolina State University is...

IEEE Winds of Change

IEEE TV has a part series of videos on wind power and it's implication. For a really good overview to the technologies and issues around wind power, these...

Multimeter

Multimeters are undoubtedly the most common item of electrical test equipment in use.  Often it is the first piece of equipment people will turn to when...

Arc Flash Calculations

Working in the vicinity of electrical equipment poses an hazard. In addition to electric shock hazard, fault currents passing through air causes Arc Flash...

Resistors

Resistors are electronic components that oppose the flow of current.  Manufactured in various types and ranges they have a wide application to electronics...

Have some knowledge to share

If you have some expert knowledge or experience, why not consider sharing this with our community.  

By writing an electrical note, you will be educating our users and at the same time promoting your expertise within the engineering community.

To get started and understand our policy, you can read our How to Write an Electrical Note