Design of Linear Integrated Circuits

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Operational amplifier - Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/Operational_amplifier

Operational amplifier
From Wikipedia, the free encyclopedia An operational amplifier ("op-amp") is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output.[1] An op-amp produces an output voltage that is typically hundreds of thousands of times larger than the voltage difference between its input terminals.[2] Operational amplifiers had their origins in analog computers where they were used to do mathematical operations in many linear, non-linear and frequencydependent circuits. Characteristics of a circuit using an op-amp are set by external components with little dependence on temperature changes or manufacturing variations in the op-amp itself, which makes op-amps popular building blocks for circuit design.

A Signetics μa741 operational amplifier, one of the most successful op-amps.

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 over $100 US in small quantities.[citation needed] Op-amps may be packaged as components, or used as elements of more complex integrated circuits. The op-amp is one type of differential amplifier. Other types of differential amplifier include the fully differential amplifier (similar to the op-amp, but with two outputs), the instrumentation amplifier (usually built from three op-amps), the isolation amplifier (similar to the instrumentation amplifier, but with tolerance to common-mode voltages that would destroy an ordinary op-amp), and negative feedback amplifier (usually built from one or more op-amps and a resistive feedback network). The power supply pins (VS+ and VS−) can be labeled in different ways (See IC power supply pins). Despite different labeling, the function remains the same — to provide additional power for amplification of the signal. Often these pins are left out of the diagram for clarity, and the power configuration is described or assumed from the circuit.

Contents
1 Circuit notation 2 Operation 3 Op-amp characteristics 3.1 Ideal op-amps 3.2 Real op-amps 3.2.1 DC imperfections 3.2.2 AC imperfections 3.2.3 Non-linear imperfections 3.2.4 Power considerations 4 Internal circuitry of 741 type op-amp

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9/23/2012 2:37 PM

Operational amplifier - Wikipedia, the free encyclopedia

http://en.wikipedia.org/wiki/Operational_amplifier

4.1 Input stage 4.1.1 Differential amplifier 4.1.2 Biasing circuit 4.1.3 Current mirror active load 4.1.4 Operation 4.1.4.1 Differential mode 4.1.4.2 Common mode 4.2 Class A gain stage 4.3 Output bias circuitry 4.4 Output stage 4.5 Some considerations 5 Classification 6 Applications 6.1 Use in electronics system design 6.2 Applications without using any feedback 6.3 Positive feedback applications 6.4 Negative feedback applications 6.4.1 Non-inverting amplifier 6.4.2 Inverting amplifier 6.5 Other applications 7 Historical timeline 8 See also 9 Notes 10 References 11 Further reading 12 External links

Circuit notation
The circuit symbol for an op-amp is shown to the right, where: V+: non-inverting input V−: inverting input Vout: output VS+: positive power supply VS−: negative power supply

Operation

Circuit diagram symbol for an op-amp

The 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, which is called the differential input voltage. The output voltage of the op-amp is given by the equation: V_{\!\text{out}} = A_{OL} \, (V_{\!+} - V_{\!-}) 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...
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