Questions tagged [operational-amplifier]

Questions relating to the construction and applications of operational amplifiers,

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45
votes
6answers
13k views

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?
37
votes
5answers
22k 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. ...
35
votes
4answers
1k 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 ...
32
votes
6answers
10k 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 ...
30
votes
2answers
123k 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/...
29
votes
5answers
4k 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 ...
29
votes
4answers
39k 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 ...
29
votes
4answers
48k 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: ...
25
votes
9answers
14k 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 ..."...
25
votes
2answers
3k 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 ...
24
votes
5answers
22k 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.
23
votes
3answers
22k 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?
23
votes
1answer
53k 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?
22
votes
11answers
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?
22
votes
5answers
54k 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 ...
22
votes
4answers
2k 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 ...
22
votes
6answers
6k 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 ...
19
votes
4answers
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 ...
19
votes
4answers
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 ...
19
votes
4answers
8k 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. ...
18
votes
5answers
26k 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 ...
18
votes
1answer
3k 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 ...
18
votes
3answers
116k 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 ...
17
votes
7answers
5k 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 ...
17
votes
6answers
57k 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....
17
votes
2answers
10k 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)....
17
votes
6answers
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". ...
16
votes
4answers
25k 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 ...
16
votes
4answers
13k 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 ...
16
votes
2answers
3k 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 ...
15
votes
6answers
5k views

Why do (microphone) preamp designs tend to limit opamp gain to max 60 dB?

Looking at many pro recording quality microphone preamps, I noticed that every design I looked at that uses an opamp (discrete or IC) limits the gain provided by the opamp to about max 60dB. While ...
15
votes
5answers
3k 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 ...
15
votes
7answers
4k 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 ...
15
votes
2answers
17k 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 ...
15
votes
3answers
946 views

How does this inverting opamp circuit with adjustible bandwidth work?

Either my textbook author is a scoundrel or I don't have the prerequisites to understand even a simple op-amp circuit. I understand how a basic inverting amplifier works and I get how the gain falls ...
15
votes
3answers
22k 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 ...
15
votes
3answers
4k views

What does this circuit do? Op-amp with transistors in feedback

I'm an electrical engineering student and I find this circuit in a guitar amplifier schematic, and basically, I'm just wondering what it does, and how one would go about working out what it does. ...
15
votes
2answers
53k 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? (...
15
votes
5answers
10k views

Op-Amp Input Resistor?

I'm reading through the datasheet for the TL064, which contains this figure on page 16: This is of course an instrumentation amplifier that apparently uses an inverting amplifier's output instead of ...
15
votes
3answers
3k 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: ...
14
votes
5answers
4k 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 ...
14
votes
4answers
2k views

Active low-pass filters — good to what frequencies?

Appendix E of The Art of Electronics, 3rd Edition (LC Butterworth filters) starts by saying that "active filters are convenient at low-frequencies but impractical at higher frequencies". They go and ...
14
votes
3answers
4k views

Why do comparators generally have higher offset voltages than opamps?

I need to compare a signal to a constant voltage; the signal ranges from 0 to 30mV, and I require a response time of 50ns at 250µV difference. The signal is a triangle wave with a slew rate in the ...
14
votes
5answers
5k views

Is it safe to connect an Arduino to the human body?

I want to create some project which uses an Arduino to collect and display ECG data. It uses two electrodes which are attached to the body (on the chest). The signal is then transmitted through op-...
14
votes
3answers
1k views

What do moving rails (voltage shifting on the rails) do to an opamp?

Since I've spent a good portion of my career trying to get opamp's rails as steady as possible at their intended voltage, I haven't really spent any time thinking about what would happen if the rails ...
14
votes
3answers
2k views

How can I measure gate capacitance?

Is there an effective way to directly measure the gate capacitance of a power MOSFET, like say the IRF530N? The way my circuit is behaving would indicate that the effective gate capacitance is ...
14
votes
2answers
4k 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 ...
14
votes
1answer
5k views

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

When looking at circuits like this one circuit http://dt.prohosting.com/hacks/what1.gif I often find (see U6-A in linked schematic) extra capacitors in the pF range slapped in parallel with the ...
14
votes
1answer
29k 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 ...
14
votes
3answers
1k 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 ...