# 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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### Op-amp gain too big, can't figure out why [closed]

We are using a 741 opamp using an inverting input. My students built a circuit, and the gain was way too high. They had taken it apart. So I had them build it in front of me. The gain is still too ...
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### What's a current feedback amplifier?

Another opamp question. Most opamps seem to be voltage feedback amplifiers (VFA), but there also seem to be current feedback amplifiers (CFA). When would you use a CFA, and what are their (dis/)...
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### When would you need a low bandwidth opamp?

This opamp has a unity gain bandwidth of 27kHz, which is by far the lowest I've ever seen. (I first misread the 7.7V/ms slew rate as 7.7V/$\mu$s, because that's the units most often used.) 27kHz ...
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### 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 ...
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### 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 ...
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### Is feedback transfer function the same as the transfer function for the whole circuit?

I have a circuit very similar to the inverting band pass filter circuit here: I was asked a question about the circuit's feedback transfer function. Is this the same as the transfer function for the ...
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### Why can't a feedback network use a capacitor? [duplicate]

Possible Duplicate: Basic Frequency Control Circuit In the following schematic, why can't R4 be taken away and the feedback network pass output feedback through C2 and R2?
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### Types of amplifier - what is the difference?

What is the difference between an open loop amplifier and a voltage follower (unity gain buffer)?
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### 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....
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### 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 ...
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### Conflicting impedances in a peak detector

Here is a peak detector circuit: Here is a scope view of what I get before the diode: Blue = input. Yellow = output of the op-amp. The op-amp saturates almost every time. There is just a small time ...
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### Does this voltage regulator use "on-off" control, or is it a voltage follower?

In Electronics A2 (GCE), we are currently studying voltage regulators. An example voltage regulator circuit is provided using an op-amp and a power MOSFET. I would judge this to be a voltage ...
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### Is it possible to make a non-inverting difference amplifier?

For a crude current sense application I am wondering whether it is possible to build a non-inverting difference amplifier without common mode offset on the output. Reason: I would like to avoid ...
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### How do I use a clipping Zener at the input of an Opamp inverting amplifier?

I have a $V_{in}$ signal for which I cannot guaranty that it would have an upper limit. I want to clip this input signal to a limit (e.g.; 8.2V) with a circuit like above. Is this circuit alright?...
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### Opamp: current flow in supply legs

Can somebody enlighten me on when and how much current flows in/out of the supply and/or ground leg of an opamp? What happens if there are resistors in those legs? Update 1: Here is the circuit that ...
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### Constant current Opamp circuit issues

I have implemented a constant current source for an high power LED. I am using the following topology. I have the following problems: Even a small noise on IN+ causes some current to pass through ...
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### Wingman Wheel with different power supply? [closed]

I have an old Wingman Formula Force running on 20V / 1.5A, and I've lost my original cord/power supply. I have 2 other supples in here, one with 12V / 2.5A Second is 22V / 1230mA (guessing that's the ...
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### OP07 unity gain

Is an OP07 unity gain stable ? I am powering it with a +/- 5V supply. I am using it to buffer a DC signal which varies slowly. Most of the modern Op-amps have their datasheets mentioning them ...
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### caveats in rail-to-rail I/O opamps?

There are a large number of opamps in the so-called "rail-to-rail" category: these either have an input common-mode range that approaches or exceeds the power supply rails, or they have an output ...
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### 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. ...
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### How to analyze this circuit in the time and frequency domain?

I came across this circuit in another post and started looking at the op amp filter and how to apply traditional circuit analysis ( using 1/jwc for capacitors) and couldn't derive the transfer ...
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### How many opamps does it take to find the peak amplitude of a signal?

I'm a beginner with EE and trying to find the peak amplitude of an electric guitar signal (0-300mV) using an Arduino's 0-5v ADC. I'm going to use the data to pulse lights in accordance with each strum ...
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### Water Meter Monitoring

Working on a project where I am wanting to monitor water meter via a magnetic sensor which will detect the spinning magnetic disc. It's very similar to the project this person has accomplished: http:...
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### Are there op amps or comparators that run on >100V?

I was using two op amps with inputs crossed as seen here: to make inverters for stepping up voltage with high efficiency. The design works well, but op amps seem to be only built for low voltages. I ...
1 vote
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### IR Demodulator Design

I am designing an IR demodulator circuit to replace the one shown in this question. Basically I want to demodulate a simple IR signal modulated at 32.678 kHz. I just need to know if the signal is ...
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1 vote
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### Calculating node voltages

This question is somewhat modified from the original which was asked by someone else. Note that there is more to this than meets the eye. The OP07 or OP070xxx is a 30+ year old op amp, the transistor ...
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### Generating thermal noise from a resistor

I'd like to create a random number generator based on thermal noise from a resistor, using an opamp to amplify the noise and an inverter to convert the resulting spikes into a digital signal. Here's ...
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### How do I protect analog circuit from relay switching noise?

I'm making a thermocouple based temperature controller. The thermocouple voltage is measured by using cold junction compensation IC LT1025 and precision opamp LT1050. The measurements are read by ...
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### Op Amp output range

Consider the following scenario: The supply voltages of op amp (rail to rail) is 5V. Amplification factor of the op amp is 100. Which means if the input is 0.01 volt, the output will be 1V. If the ...
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### 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 ...
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### Homebrew differential 'scope probe

I may be able to get my hands on an old 600MHz LeCroy oscilloscope. However, it doesn't have any probes. Is it feasible to make an active differential probe for it using a high-speed op-amp, like the ...
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### Input impedance of an op Amp

I noticed that the input impedance of an op Amp is extremely high. Why is that so?
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### Simple and powerful audio amplifier around BA4558?

I have two BA4558 ICs from an old home stereo. I tested them with simple negative feedback circuit for each channel and with power supply of +/- 6V. The speakers I used are most likely with 8 ohm ...
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### Minus Voltage & Ground

Sometimes i come across different notations in Op Amps. Sometimes they are fed by V and ground, sometimes +V and -V. I am confused. Does ground mean minus? Look at here: http://www.williamson-labs....
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### Why would a Diff Amp require both inputs to have a DC path to GND to work?

I'm looking at using a NI PXI-6255 DAQ card and I noticed in the manual it says "Both inputs of the (diff amp) require a DC path to ground in order for the (diff amp) to work." Is this a common ...
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### Opamp driving a capacitive filter load

I know that opamps can be unstable when driving capacitive loads. The input to the opamp is more complicated than the schematic shows, but an unfiltered full wave bridge rectifier is the proper ...
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### Odd Op-Amp Behavior

I was working on a project with a LM741N and I accidentally hooked up the circuit wrong, and I noticed some strange behavior. I was trying to amplify the 3.3V output of a micro-controller to 6V, but ...
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### Op amp rectifier : transfer function and output impedance

I'm working on an EE student project which uses a rectifier to keep the peak value of a sine wave. You can find a PSpice pic of the schematics below (Ve is the input (1kHz), Vs is the output). Op amp ...
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### How does this voltage comparator work?

Can somebody explain to me, how the following voltage comparator works? I believe to recognise U4A as an inverting Schmitt trigger, but how everything fits together escapes me... Should the ...
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### How do I invert the output of this current sensor using the other side of the LM358?

Referencing a design that uses a more expensive OpAmp, I have put together (in simulation) this current sensing circuit that uses one half of an LM358. I would like to use the other half of the LM358 ...
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### How to divide signal level from function generator

I looked for this answer but was unsuccessful so I want to ask the experts here. I have configured an op amp in non-inverting mode (the first in a chain of 3 stages). It is for amplifying extremely ...
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### Trouble chaining multiple low noise op amps

I want to experiment with receiving ELF signals. In particular 76Hz. The goal is to attach a coil of a few thousand turns of magnet wire, place it on the ground, and read the signal level. My ...
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### THS6002 "Dual Differential Line Drivers and Receivers". Output: 15 MHz

I made ​​a PCB with the THS6002 chip "Dual Differential Line Drivers and Receivers". I copied the application example of figure 59 in the datasheet (page: 34), with three differences: the transformer ...
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### Replacing a LM741 op amp with higher quality op amp?

I am a complete novice with electronics...but i'm looking to build a replica of a discontinued TC Electronic Integrated Preamp. Its a basic line booster with Volume, Bass and Treble but sounds great ...
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### Postive input ==> Positive and Negative output

I was watching some tutorials on thesignalpath.com and came across something that I didn't quite understand (even after it was explained). toddrharrison August 21, 2011 at 6:29 PM Answer to first op-...
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### How does this OP-AMP non-inverting amplifier work?

In this non-inverting circuit at page 6 of "A Single-Supply Op-Amp Circuit Collection (SLOA058)": I've found out the equation to be (assuming Vcc=+5 V):  Vo=(Vin-2.5)*\frac{R_{1}+R_{2}}{R_{1}}+2.5 ...
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### Finding a current sense differential amplifier [closed]

I want to measure the voltage drop across a shunt resistor, amplify it to 50 times the original value, and feed that (0 - 5 V) to an ADC. I'd prefer to do the "high side" current sense method (rather ...
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### Why is this Op Amp generating a 12kHz signal?

I'm a bit of a noob, but am trying to manually build an IR receiver circuit from a photo diode and a few other parts (the circuit im trying to reproduce is shown @ http://online.physics.uiuc.edu/...
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### Detecting a 15KHz burst with logic output

I want to build a simple and ultra low cost circuit that can detect a timed (let's say 200ms) burst of a single sine frequency - say,15KHz. Amplitude will be around AC ~1Vp-p. Detection will give a ...
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