Questions tagged [operational-amplifier]

Questions relating to the construction and applications of operational amplifiers,

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47
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?
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 ...
18
votes
5answers
27k 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 ...
9
votes
3answers
43k views

Analog voltage level conversion (level shift)

I have a joystick that puts out analog voltage somewhere between 1.5V and 3.5V. I want to transform this range of voltage to control a motor controller that takes analog voltage between 0V and 5V. ...
33
votes
6answers
11k 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 ...
1
vote
1answer
333 views

Transfer function of a LM380 power amp

This is an exam question. Our professor has some generator of tests and out of the blue this beast came. We couldn't ask for the clarification, being an exam question, but from what I can see it ...
24
votes
5answers
23k 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.
12
votes
6answers
16k 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) ...
10
votes
6answers
7k views

How do I sample a -2 V to +2 V analog signal with a PIC microcontroller?

I am using a PIC micro with a 10bit ADC to take readings from an analog signal with a frequency less than 300 hz. However that analog signal is in the range of -2 V and +2 V. How can I condition the ...
3
votes
3answers
4k views

How does this Push-Pull amplifier work?

I'm reading about op-amp circuits that use negative feedback from this article (question no.19). What confuses me is that the negative feedback for the Op-amp (which is being used to reduce ...
12
votes
6answers
35k 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 ...
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 ...
10
votes
6answers
12k views

How does this constant current sink actually work?

I have implemented a constant current source and it works wonderfully, but I was just hoping to try and understand it a little bit more! Here is the circuit in question: I have tried doing some ...
17
votes
6answers
58k 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....
5
votes
3answers
42k views

How do you determine the input impedance for an inverting amplifier?

Essentially I am getting confused trying to do the sums for an op amp with a gain of 10dB and an input impedance of 1kohm. I worked out that \$\frac{V_{out}}{V_{in}}=-\frac{R_{2}}{R_{1}}\$ because \$...
18
votes
3answers
118k 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 ...
2
votes
5answers
1k views

Design of a discrete BJT current buffer for low-current op amp

I built and simulated this BJT current buffer for an opamp based on examples I found in various places online: Link to simulation of above schematic It simulates fine, but I am pretty sure it will ...
0
votes
2answers
2k views

Making dual power supply from single for opamp?

For the circuit of opamp 741. we have to supply the dual power for it. How can I make a dual power supply from single. For example, make a (+9V)-GND-(-9V) from single 9V battery ?
3
votes
4answers
18k views

Voltage Controlled Current Source integrated circuit? Exists?

Does anyone know of a Voltage Controlled Current Source IC? Or do you know how I can build one with as few other components as possible taking up a minimal amount of space? current range needed is ...
22
votes
5answers
55k 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 ...
13
votes
3answers
44k views

Scale 30-50 mV signal to 0-5 V range

I have a CO2 sensor that output signal values 30-50 mV. I need to translate these voltages to 0-5 V for my microcontroller with the highest resolution. I understand that I can amplify the ...
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 ...
3
votes
3answers
24k views

How to amplify and offset the voltage in an opamp?

I need to amplify a voltage, which comes from a DAC and is 0-2.5V and scale it 0-25V in an operational amplifier. After amplified, I need to offset it -1.25V, so the final voltage is -1.25 to 23.75V. ...
9
votes
1answer
475 views

What is the difference between “opamp” and “comparator”?

In electronic part seller websites, I see that there are two separate categories for opamps and comparators. As far as I know, an opamp itself is already a comparator if you don't connect a negative ...
-3
votes
4answers
202 views

Find the transfer function of this 3th order filter [closed]

I'm working on a project and I need to find the transfer function fhe following filter (as a function of the value of the capacitors and resistors). How can I find that?
3
votes
2answers
1k views

Can I use a UA741 here?

I need to pass a domestic -10dbV audio signal (it should oscillates between -447mV and +447mV) to a microcontroller's ADC which only accepts signals that oscillates between 0V and 5V. I think that the ...
3
votes
3answers
3k views

Do I really need the open loop output impedance of an op amp?

There are several answers on the internet and here on how to calculate the output impedance of the opamp with a given feedback. My intention, though, is to find this value with an open loop ...
3
votes
4answers
3k views

Basic Frequency Control Circuit

How does R4 prevent the output voltage drifting towards one of the supply rails to the op amp? I understand that R4 has to have a high resistance but I do not know why? Here is the schematic which is ...
4
votes
6answers
4k views

What is the purpose of this op amp?

I am trying to build a pH meter using the below circuit. I am trying to understand the function of Op Amp U1. As I understand it, the LM4140A-1.0 is a voltage reference outputting 1.024V, which is ...
3
votes
4answers
3k views

Understanding Op-amp Negative Feedback

Have a look at the diagram above. It shows an op-amp with negative feedback. Ignoring the feedback loop for now, the voltage (pressure) coming from the 5V battery, acting on the inverting pin, ...
2
votes
0answers
783 views

Complete Noise Analysis: to find the minimum detectable signal of a TIA

Problem Statement: my aim is to digitalize a 10ns narrow pulse coming from a photo diode with current ranging from 10nA-70mA, as its impossible to cover this dynamic range of >60dB using a single TIA ...
2
votes
2answers
1k views

Which is the correct voltage reference for a single supply instrumentation amplifier?

I'm working on using the TI INA333 in a single 3v supply configuration. I need to create a "mid supply" (half V+) for the REF pin. I have thought of 3 ways to do this: Voltage divider with ...
15
votes
2answers
18k 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 ...
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: ...
18
votes
4answers
27k 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 ...
7
votes
6answers
13k views

Is a square wave still considered DC?

Say I have a logic-level square wave, where 0V is "low" and 5V is "high". I'm pulsing this at a constant 60Hz, 50% duty cycle. My intuition says that since the voltage never goes negative, it's a DC ...
24
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?
15
votes
4answers
23k 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
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 ...
26
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 ...
9
votes
2answers
3k views

Use of 100K ohm resistor along with 0.1uF capacitor?

In the circuit diagram below, why is there a 100KΩ resistor (NOT R2) connected to the capacitor? To my understanding the capacitor-resistor act as a high pass filter to block the DC offset of ...
6
votes
1answer
9k views

Transfer function for inverting amplifier

After reading this answer I wanted to know how the transfer function for an inverting amplifier was derived. I found this page, but it leaves me unsatisfied. Their proof is just two lines, and the ...
3
votes
2answers
6k views

Precision high speed peak detector

As a follow-up to my previous question, where I seek to determine the amplitude of a 2 MHz sine wave, I've settled for an op amp based solution. To recall, my input has a maximum 240 mV amplitude -- ...
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". ...
10
votes
3answers
19k views

Input impedance of inverting amplifier clarification

Take a standard inverting amplifier: I'm unclear on what the input impedance is. At first I thought it was the equivalent resistance from the inverting input to the ground, which would be Rin || Rf, ...
10
votes
6answers
14k views

Input voltage range of opamps

I understand that, for an ideal opamp, Vo is bounded by Vee and Vcc (i.e.; Vee < Vo < Vcc). But, what about the input voltage range? What is the allowed input voltage range in which opamp works ...
5
votes
2answers
2k views

Why does bringing TL072/TL074 non-inverting input low cause output to go high?

I was building a circuit using a Texas Instruments TL074 as a comparator, when I noticed some strange behavior. I isolated the chip and tested it with a couple of potentiometers. Basically, when I put ...
5
votes
3answers
322 views

Efficiency of obtaining differential signalling from a single-ended manufactured transducers

This will be a conceptual question. I'm sometimes dealing with data-acquisition of transducers, like strain gauges, accelerometers ect. sort of sensors. Most of these sensors have their own precision ...
3
votes
2answers
557 views

How does a Miller cap physically create a pole in circuits?

If we consider a single NMOS transistor (with its source terminal grounded) and a Miller cap (C) between its input (gate) and output (drain) nodes, circuit theory says that this Miller cap will be ...
7
votes
1answer
684 views

How to construct high speed logarithmic amplifiers

Objective : Converting laser pulses from photo diode ranging from 10nA - 100mA to digital format, for measuring pulse width exactly. Pulse width 10ns-150ns and repeating at a rate of >20us up to ...