Electrical Engineering Stack Exchange
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Questions tagged [operational-amplifier]

Questions relating to the construction and applications of operational amplifiers, which are DC-coupled, high-gain electronic voltage amplifiers with a differential input and, usually, a single-ended output.

An operational amplifier is a DC-coupled, high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output.

An op-amp produces an output potential that is typically hundreds of thousands of times larger than the potential difference between its input terminals. Operational amplifiers had their origins in analog computers, where they were used to perform mathematical operations in many linear, non-linear, and frequency-dependent circuits.

The popularity of the op-amp as a building block in analog circuits is due to its versatility. By using negative feedback, the characteristics of an op-amp circuit, its gain, input and output impedance, bandwidth, etc. are determined by external components and have little dependence on temperature coefficients or engineering tolerances in the op-amp itself.

(Excerpted from Wikipedia)

Further reading

Texas Instruments application report SLOA011: Understanding operational amplifier specifications

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Reasons not to use a 741 op-amp?

Simple enough question. Why not use a 741 op-amp in a target circuit or anyone's target circuit? What are the reasons not to use it? What might be the reasons to still choose this part?
Andy aka
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What is input and output impedance of an opamp?

I have never understood input and output impedances of an op-amp. If anyone can explain what these two terms mean in an op-amp I'd highly appreciate it. Thank you! http://www.eecs.tufts.edu/~dsculley/tutorial/opamps/opamps5.html
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Why would an op-amp use BJTs over MOSFETs?

I've always been told that ideally, op-amps have infinite input impedance. So when I was looking at the LM741's transistor level schematic, I was confused when they used BJTs instead of MOSFETs. Wouldn't using a BJT result in current flowing into…
Nate
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Designing a *linear* MOSFET driver stage

I'm looking for a MOSFET driver circuit that can be placed between an op-amp and a power MOSFET to operate the transistor as a linear amplifier (as opposed to a switch). Background I'm developing an electronic load circuit that must be able to step…
scanny
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Identifying Source of Periodic Artifact at Op-Amp Output

My MAX44251 dual op-amp has a very small unwanted 131KHz periodic artifact at the output, seemingly regardless of how it's configured. My assumption was EMI, but I can't see this 131KHz signal on any other part of the circuit. I've also tested this…
Keegan Jay
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What is the purpose of a resistor in the feedback path of a unity gain buffer?

I often see unity-gain followers with a resistor in the feedback path. For an ideal op-amp, of course, there is no current into the input, and this resistor does nothing. What is its effect with a real op-amp, and how do I choose its value? What…
nibot
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What is the advantage of the inverting opamp circuit over non-inverting one?

Op amp circuits are designed to achieve a specific gain regardless of the differences between individual op amps. One very common circuit has a gain of -R2/R1. Here's a (corrected) schematic: Another common configuration has a gain of R2/R1+1 and…
Dov
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Choosing resistor values for inverting amplifier and why?

The gain here is A = -Rf/Rin. However, lets say I want a gain of 10 V/V. Which resistor value would you choose and why? I know that you could have infinite number of combinations for these resistors but why would some one use specific value. i.e Rf…
dr3patel
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What's the uA741's appeal?

OK, so the uA741 is 42 years old now. For its time it may have been a great opamp; the requirements weren't as high as today, and there was far less competition. But I was wondering what's the 741's appeal today. it's slow. GBW 1MHz, slew rate…
stevenvh
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Do op amps need one bypass capacitor or two?

As with other ICs, it's standard practice to place bypass capacitors near the supply voltage pins of op amps. But I've seen conflicting opinions on how to properly bypass an op amp (here, for example). Some people suggest putting a single capacitor…
Adam Haun
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Does this photodiode circuit work?

Oli used this circuit in an answer, and it pops up a lot on Google images too. But does it work? If it does a theoretical explanation will be welcome.
stevenvh
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What is noise gain, really? And how is it determined in the general case?

UPDATE: This question triggered what might fairly be called a research obsession for me. I've gotten pretty close to the bottom of it I think, I've posted my findings as an answer below. There was a similar question here but it did not ask for nor…
scanny
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Why are op amps used so frequently in analog electronics?

I've read in several books and papers the observation: "Op amps are the bread-and-butter of analog electronics", or "... op amps are the most commonly encountered building block in analog circuits ..." and to that effect. Although my experience is…
scanny
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How to disable a single op-amp in dual packaging?

I am using a dual op-amp package in a circuit, however I only need to use one. Is there anyway to disable the other op-amp so it doesn't inject electrical noise in my circuitboard? I think grounding the positive input and setting the op-amp into…
user1207381
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What's special about "unity-gain stable"?

As mentioned in opamp datasheets, like this one. I would think stability is a problem at higher gains, due to oscillation. What are the problems with unity-gain?
Federico Russo
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