Design of Linear Integrated Circuits

Topics: Operational amplifier, Differential amplifier, Amplifier Pages: 31 (10403 words) Published: December 19, 2012
Operational amplifier - Wikipedia, the free encyclopedia

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.

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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Operational amplifier - Wikipedia, the free encyclopedia

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 Differential mode 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


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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