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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.

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77 votes
8 answers
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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's user avatar
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48 votes
2 answers
167k views

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/...
user734861's user avatar
47 votes
5 answers
33k views

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. ...
Nate's user avatar
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41 votes
6 answers
17k views

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 ...
scanny's user avatar
  • 7,172
38 votes
6 answers
60k views

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 ...
nibot's user avatar
  • 1,720
38 votes
4 answers
2k views

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 ...
Keegan Jay's user avatar
  • 1,280
37 votes
4 answers
60k views

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: ...
Dov's user avatar
  • 1,671
34 votes
5 answers
82k views

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 ...
dr3patel's user avatar
  • 1,652
31 votes
2 answers
21k views

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)....
Adam Haun's user avatar
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30 votes
5 answers
5k views

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 ...
stevenvh's user avatar
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30 votes
2 answers
5k views

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 ...
user1207381's user avatar
30 votes
6 answers
16k views

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 ...
scanny's user avatar
  • 7,172
29 votes
9 answers
19k views

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 ..."...
scanny's user avatar
  • 7,172
29 votes
6 answers
30k views

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's user avatar
  • 146k
26 votes
3 answers
34k views

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's user avatar
25 votes
4 answers
3k views

Illustrating op amp feedback without control theory

We are teaching op amps in a high school class, before calculus. So we can't use control theory to teach how op amps respond. All the same, I would like to have an intuitive explanation for how a ...
Dov's user avatar
  • 1,671
25 votes
2 answers
30k views

Single supply op-amp audio amplifier

I am trying to create an op-amp amplifier that would work from single 5V supply, and would be able to amplify -100mV to +100mV audio signal to around a 1V peak-peak or so. I've came across this ...
Golaž's user avatar
  • 2,007
24 votes
2 answers
78k views

How do I correct the offset voltage of op-amps which have no explicit offset-null pins?

Not all op-amps have explicit offset-null support, but all op-amps have an offset voltage. This is exactly my practical circuit: How do I correct the offset voltage of TL084 in this circuit? (...
hkBattousai's user avatar
  • 14.2k
24 votes
3 answers
148k views

What is "offset null" in IC 741?

What is Offset null in 1st and 5th pin in IC 741 (Op-Amp)? Why it is used, though it is not used in many circuits? Give me explanation regarding the offset null! Why offset voltage was formed in IC ...
Abishek ram R's user avatar
24 votes
1 answer
55k views

What's input bias current in opamps?

Is it the current you have to drive in the input to get a specific, defined voltage at the output? And don't the currents cancel each other when applied to both inputs?
Federico Russo's user avatar
24 votes
2 answers
12k views

Review request: DIY DC to 50MHz differential oscilloscope probe

Given the cost of proper differential probes, i've decided to make my own. The requirements are: DC to 50 MHz 3db bandwidth A few selectable input voltage ranges, from 3V pk-pk to 300 V pk-pk ...
jms's user avatar
  • 8,661
23 votes
5 answers
50k views

What is the difference between operational, differential, and instrumentation amplifiers?

RS Components lists three categories of similar amplifiers: Operational Amplifiers, Differential Amplifiers, and Instrumentation Amplifiers. I think that there should be a single section called ...
quantum231's user avatar
23 votes
5 answers
41k views

Difference between differential op amp and comparator

What is the difference between a differential op amp and a comparator? I know a comparator can only give me two values (the supply values). The differential op amp amplifies the difference between ...
user25282's user avatar
  • 287
21 votes
11 answers
7k views

Op-amp tutorial for electronic noobs?

Can anyone point me to a tutorial for electronic noobs that explains how to use op-amps and what I can do with them, besides amplification?
Nikolaus Gradwohl's user avatar
21 votes
4 answers
11k views

When is it an instrumentation amplifier (In-Amp) and not an operational amplifier (Op-Amp)?

I've seen a number of different configurations for instrumentation amplifiers, including 2 opamp versions. This is also one. But it's just a differential amplifier preceded by input buffers. ...
Federico Russo's user avatar
21 votes
5 answers
45k views

Inverting buffer with op-amps

I know that it's easy to make a unity gain buffer with an op-amp (as a voltage follower): simulate this circuit – Schematic created using CircuitLab I also know that it's easy to make an ...
Greg d'Eon's user avatar
  • 3,847
20 votes
5 answers
3k views

What is the true circuit behind an opamp?

So, first year EE student, and I just learned about op-amps. I understand the ideal model, and know how to analyze them, and understand the idea behind them/the circuit that we were shown that is ...
Mahmud Ahmad's user avatar
20 votes
1 answer
4k views

OP amps distort sine wave

I am creating a simple circuit in order to amplify the signal from an electret microphone and then add a 2.5V bias to the signal. The problem I'm having is that the signal from the mic is distorted as ...
SjoerdvdBelt's user avatar
19 votes
8 answers
4k views

Why are kiloohm resistors more used in op-amp circuits?

In operational amplifiers working in the negative feedback configuration, the voltage gain depends on the "ratio" of resistances. In most textbooks I have seen that both feedback and input ...
MAJID AHMAD's user avatar
19 votes
4 answers
2k views

What is the use of an op-amp whose output and inverting input are connected to ground?

I am in first year of Engineering school and I was given an assignment containing this circuit, which drives pressure sensors in a pitot tube : I am struggling to understand the whole circuit, and ...
Magix's user avatar
  • 353
19 votes
6 answers
68k views

Why is feedback required in op-amp circuits?

I understand that, in order for an op-amp to function correctly, a DC feedback loop from the output to either the inverting or the non-inverting input (depending on the external circuitry) is required....
user1083734's user avatar
19 votes
7 answers
15k views

How make a dual +-12V supply from a 24V SMPS

I'm trying to power a home-made load cell transmitter using a 24V single SMPS. I need to make +12, 0 and -12 Volts that are capable of 50mA. I wish to power multiple channels of opamps and bridges. I ...
Ohbhatt's user avatar
  • 301
18 votes
8 answers
17k views

Op-amp input resistor?

I'm reading through the datasheet for the TL064, which contains this figure on page 16: This is an instrumentation amplifier that apparently uses an inverting amplifier's output instead of a ground ...
In silico's user avatar
  • 1,387
18 votes
3 answers
6k views

Why doesn't LTSpice predict this op-amp oscillation?

I'm developing a circuit to act as an electronic load for bench testing power supplies. An earlier question about how to test this circuit received several very useful answers and can be found here: ...
scanny's user avatar
  • 7,172
18 votes
1 answer
37k views

Subtracting two voltages using an op-amp

I'm essentially a digital guy, and am used to using a comparator to compare two voltages and give a high or low depending on their relative values. Now instead I want to subtract one voltage from ...
tcrosley's user avatar
  • 48.2k
18 votes
4 answers
15k views

Is this a good design & layout of an active differential 'scope probe?

This question is an extension of Homebrew differential 'scope probe. I thought I should make this a new question though. I need to measure a 100Mb/s LVDS signal to check its integrity. I will try to ...
Rocketmagnet's user avatar
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17 votes
5 answers
7k views

Why can't this LM324 op amp reproduce a signal above a certain frequency?

There seems to be no shortage of circuits like this that attempt to use an R2R as a DAC and an op. amp. as an output buffer. These make sense to me so I decided to try and construct one. I ...
Eric Urban's user avatar
  • 1,249
17 votes
3 answers
3k views

Why does this op amp stop working after some time?

I have an audio streaming device I bought that has analog audio output that is way too low (it’s supposedly line level, and I’m not the only one who’s complained about this). I’ve been using this as ...
nsayer's user avatar
  • 1,593
17 votes
7 answers
5k views

Op-amp inverter followed by buffer. Why?

In a schematic I've been trying to understand I came across this sub-circuit: It's an op-amp inverter directly followed by a buffer. VIN comes from a DAC in a microcontroller and this circuit ...
mcmayer's user avatar
  • 337
17 votes
6 answers
50k views

How are positive and negative feedback of opamps so different? How to analyse a circuit where both are present?

In an opamp, feedback on the positive input places it in saturation mode and the output is of the same sign as V+ - V-; feedback on the negative input places it in "regulator mode" and ideally Vout is ...
Mister Mystère's user avatar
17 votes
6 answers
4k views

How do professional designs compensate for offset voltage in opamps?

I am new to electronics and have been told in class to always add precision potentiometers to compensate for input offset voltages in opamps for signal conditioning. My concern is that this offset ...
Daniel Vela Jarquín's user avatar
17 votes
1 answer
15k views

What is the purpose of a capacitor in the feedback path of a unity gain buffer?

First time using this site, I'm an EE student and have been studying opamps. So far in class we have only discussed 'ideal' opamps, but I saw an opamp with this layout and was wondering if anyone ...
Dragon4th's user avatar
  • 173
16 votes
8 answers
9k views

Is it possible to combine two 8 bits DACs together to create a 16 bit DAC, one byte of the 16 bit word shall be sent to each of them

For two DACs, one being sent D0-D7 and the other being sent D8-D15, with power supply being 5V, if 5V is added to output of 2nd DAC and then the two DAC outputs are summed, should result in a 16 bit ...
quantum231's user avatar
16 votes
6 answers
23k views

Stability problem in unity-gain opAmp

As a part of a controlled power supply for hardware-in-loop testing for a student driven project, I had to develop a current buffer (voltage follower) which could source up to 1 A. I had the (bad) ...
svilches's user avatar
  • 529
16 votes
6 answers
2k views

How to tell what configuration a transistor has in a complicated circuit

Apparently transistor Q15 in the following circuit is in common collector mode (well, actually it says it's an emitter follower but my understanding is that this is the same thing as common collector ...
Urthona26's user avatar
  • 353
16 votes
5 answers
1k views

Are the offset voltages in a dual/quad op amp correlated?

On a single piece of silicon on which there is more then one op amp, are the input offset voltages at all correlated, i.e. would they be expected to be same direction and similar magnitude?
crj11's user avatar
  • 5,616
16 votes
6 answers
2k views

"Standard" components...?

In class we are designing a few different circuits and it uses some diodes and opamps. Everything is fine on paper and everything makes sense. These are only ever refereed to as a "diode" or "opamp". ...
binarysmacker's user avatar
16 votes
1 answer
18k views

Understanding op-amp circuits with extra capacitors in the feedback path

When looking at circuits like this one (source: prohosting.com) I often find (see U6-A in linked schematic) extra capacitors in the pF range slapped in parallel with the feedback resistors, although ...
jilski's user avatar
  • 553
16 votes
2 answers
5k views

Stability (phase margin) analysis in real feedback circuits

So I had a bright idea of using negative feedback to control offset current in my data acquisition circuit. Sure, you could do this in software, but removing the offset at the input stage would ...
Ben Voigt's user avatar
  • 2,930
16 votes
3 answers
2k views

Tips on analyzing circuit with multiple op-amps and bjts

In a homework exercise I need to sketch the Vout-vs-Vin graph, having it first obtained analytically. I know that Ur and Vin are both nonnegative, and the circuit is shown here: It seems like there ...
Emir Šemšić's user avatar

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