Op amp

An op amp ("operational amplifier") is a very high gain voltage amplifier ( the normal type ) usually with differential input, and response from DC to 1 Meg Hz or more. Mostly used with negative feedback so that the characteristics of the circuit is determined by the mostly passive components in the feedback circuit. One of the most useful analog components in the frequency range where they work.

Great for amplifying weak signals from sensors to a more useful level. Also used in filters, integrators, etc.

Quick Summary

• Many sensors need an amplifier to "buffer" their output signal. Often a single op amp is adequate. For very weak signals, you may want a "difference amplifier" or "instrumentation amplifier".
• All ADCs need an anti-aliasing filter on their input. Often a single op amp, 2 caps and 4 resistors is adequate.
• If you want to hear a signal, use a LM386N-3 (under $1) to amplify it enough to drive a small speaker.
• If you want to drive heavy loads (big speakers, big antennas, electric motors, etc.), too heavy for typical op amps to drive, use op amps to amplify the signal to the desired voltage, followed by power transistors to drive the load [Veselinovic].

Details

Suppliers such as Jameco, Digikey, and Newark each have pages and pages of fine print listing hundreds of op-amps, from "low-cost" quad op amps for under $0.40 each to "hi speed precision" op amps for well over $10 each. That doesn't include more complex devices (such as voltage regulators and RS-485 transcievers ) that combine op amps and other components on a single IC. Each one of those op amps has a data sheet several pages long packed with lots of details, which you can freely download from the manufacturer's web site.

"But in reality, there are only two important specifications that you should initially consider when selecting an op amp for your active, low-pass filter. ... Gain Bandwidth Product and Slew Rate." [Baker 2003]

Some General Links

• Operational Amplifiers: Theory and Practice, Second Edition -- Good free text book on op amps from mit
• Operational amplifier From Wikipedia, the free encyclopedia ( inc. Schematic and Picture )
• [http://en.wikipedia.org/wiki/Operational_amplifier_applications Operational amplifier applications From Wikipedia, the free encyclopedia}
• Operational amplifier
• LT1168 Programmable-Gain Precision Instrumentation Amplifier - Low Power, Single Resistor Gain Programmable, Precision Instrumentation Amplifier
• LT1114 Low Power Precision OP-Amps are used for amplification and filtering of the signal - Dual/Quad Low Power Precision, Picoamp Input Op Amps
• Wikibooks:Op-Amps has a "quick design process" using Daisy's theorem: "The sum of the gains = +1 in a properly-designed op amp circuit."
• "Some Op Amp Audio Design Issues" by Terry Ritter
• "Op Amps for Everyone" Great free book that describes a large number of Op-Amp circuits including single rail variation. A pay version is available at Amazon. I don't know what the differences are between the two versions.

designing the circuit around the op amp

• Daisy's theorem: standard op-amp design

• "APPLICATION NOTE 738: Minimizing Component-Variation Sensitivity in Single Op Amp Filters"

CookBook of Circuits ( links )

OpAmp Links

selecting the appropriate op amp out of the hundreds (thousands?) available

• "Select the Right Operational Amplifier for your Filtering Circuits" by Bonnie Baker 2003

• "Choosing an op amp: it's no longer a trying task" by Bill Schweber 1995

• Basic electronics components list lists 10 of the most common op-amps.

• "How to choose the right bipolar op amp" by J. Scott Elder 2005-12-23

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