What is Opamp: Definition and 151 Discussions

An operational amplifier (often op amp or opamp) is a DC-coupled high-gain electronic voltage amplifier with a differential input and, usually, a single-ended output. In this configuration, an op amp produces an output potential (relative to circuit ground) that is typically 100,000 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 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 tolerance in the op amp itself.
Op amps are used widely in electronic devices today, including a vast array of consumer, industrial, and scientific devices. Many standard IC op amps cost only a few cents; however, some integrated or hybrid operational amplifiers with special performance specifications may cost over US$100 in small quantities. Op amps may be packaged as components or used as elements of more complex integrated circuits.
The op amp is one type of differential amplifier. Other types of differential amplifier include the fully differential amplifier (similar to the op amp, but with two outputs), the instrumentation amplifier (usually built from three op amps), the isolation amplifier (similar to the instrumentation amplifier, but with tolerance to common-mode voltages that would destroy an ordinary op amp), and negative-feedback amplifier (usually built from one or more op amps and a resistive feedback network).

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  1. J

    Engineering Question on Opamp homework problem: Find Iout between these two Opamps

    Hi, so my objective is to find Io, and I've attached a picture of my work. Here is my question: At the point Vo1, if I use the equation for finding the output voltage for a non-inverting op amp I end up getting this: $$V_{0{1}}=\left( 1+\frac {r_{f}} {r_{1}} \right)V_{s1} = \left( 1+\frac...
  2. altruan23

    Engineering Why is a differential amplifier considered the same as a subtractor?

    So after using superposition and setting the ratio R2/R1 = R4/R3 the same or R2=R4 and R1=R3,i come to the eq. for output voltage Vout= R2/R1 * (V2-V1) or R4/R3(V2-V1). And in the book foundations of analog and digital electronics by agarwal and lang, they are saying that this circuit is a...
  3. altruan23

    Engineering Opamp adder circuit: Where does the "-" come from?

    So i used KCL and both currents are flowing into the node, and then leaving together to go to the resistor R3. So my eq can be seen in the picture. I was looking in a book and they had a minus infront of the parantheses. Is the current flowing from R3 into the node??
  4. altruan23

    Engineering OPamp circuit - how to simplify this term?

    So this is the circuit. And here i tried to calculate Uout/ Uin , any suggestion how to simplify this term?? I used Uout= Uin * (1+ Z2/Z1)
  5. J

    What is the Mystery Opamp in this Vintage Equipment?

    Hi, pals! I'm in process of restoring vintage equipment. And I was failed to identify one of the operational amplifiers. Does anyone have any idea what kind of animal this is? This is link to opamp photo: https://postimg.cc/HVZ2hjRm
  6. Stonestreecty

    Heavy Amplifier Circuit Oscillation Happened

    Hi, all I am experimenting with audio amplifiers for a while now. I learned how to do an operational amplifier with discrete components and understand all its section and sub-circuits, recently. Then I decided to just skip the hard part and use operational amplifier and output power stage for an...
  7. Callum Plunkett

    Engineering Opamp Output Offset: Solving for Rf in Circuit with Unknown Feedback Resistor

    I’ve been given the attached question and equation in regard to output offset. I know all the required values apart from Rf. Normally id assume Rf was the feedback resistor however that (as far as I can tell from the circuit) is marked as R2. Would I be right if I assumed this value was Rf =...
  8. anubhavsingh

    CMRR in open loop and closed loop configuration of opamp

    For an opamp in open look configuration, Here Ad should be equal to open loop gain of opamp and Now consider the closed loop config of opamp (negative feedback used): However, Ad is closed loop gain here (according to Sedra Smith) and In terms of open loop gain, A is open loop gain...
  9. song youngill

    Engineering How can I find DC gain via AC simulation in LTspice

    I use this netlist and simulation result came out as shown. I need to find the dc gain here and circuit diagram, but I'm not sure how. I would be very grateful if you could give me the answer.
  10. P

    Engineering Finding out the input impedance in a negative feedback op-amp

    In this case, there is negative feedback. ##V_{out}## is almost equal to ##V_{in}## in this case. But I really can't understand how to even proceed to find out the input impedance in this case, from the equation I know. Can someone help me out in figuring how should I proceed?
  11. J

    Engineering Basic opamp design problem ##V_{output} = 3V_1 - 2V_2##

    Here I let ##R_2 = 2 ## kohms and ##R_1 = 1## kohms. Using this suggests that ##R_3 = 0## and ## R_4 = 1 ## kohms (?!) The resulting circuit is Is this the correct way to solve this? PS : I just realized that I have interchanged ##V_1## and ## V_2## in the diagram!
  12. F

    How to derive a log-antilog opamp square law transfer function?

    Firstly, this is not a homework question. I found a worksheet online with an example of a square law circuit built using log-antilog operational amplifiers. I tried to derive the transfer function but I can't seem to eliminate the reverse saturation current term ##I_S##. I would really...
  13. Boltzman Oscillation

    Engineering How can I find the open loop voltage gain of this opamp?

    The open loop voltage gain is given as : $$ u(s) = \frac{u_o}{1+\frac{s}{w_o}} = \frac{100}{1 + \frac{s}{40}}$$ Where u_o is the d.c. voltage gain and w_o is the pole. The op amp that is given is: And I am told to use the non ideal op amp model as follows: Well my guess is that I can find the...
  14. J

    Engineering Input and Output Impedance of an Opamp Circuit

    I know for ideal opamp the input Z is infinite, and output Z is 0, but not sure about this opamp.
  15. J

    Engineering Voltage across the output resistor for this opamp circuit

    Here is question: Find voltage across R3 options: 10V 11V 5V 2V Attempt: No current flows through Opamp, so 1mA flows through R3, this gives voltage across R3 = 1ma * 1K = 1V. But that is not in option. Where am I wrong? No current flows inside or outside opamp, right?
  16. paulmdrdo

    Engineering Why Does a Second Order Opamp Circuit Show Contradictory Derivatives?

    I was trying to understand the way this problem was solved and I got confused with the latter part of the solution. I encircled the part that confused me. They seem to contradict each other. If dv(0+)/dt = 0 why is it dv(0+)/dt = -1 in the other one? Please explain. TIA...
  17. D

    How to make a comparator out of an opamp

    I have an operational amplifier. I am Trying to make a comparator out of It. I built a voltage divider to provide Different voltages. But I either get The same voltage output regardless Of input or the voltage is too high I think. How do you make a comparator out of an operational amplifier?
  18. dvscrobe

    Engineering Time Constant of an Opamp Circuit

    Homework Statement : [/B] Find the time constant of an inverting op amp with C = 50uF, Ri = 200 Ohms, Rf = 20 Ohms. This is a problem I have found in a prep book for the Fundamentals of Engineering Exam (Electrical component). The book gives the answer as time constant = Rf * C. I am not...
  19. Boltzman Oscillation

    What is the gain error for this opamp driven by a voltage

    Homework Statement The op amp has a near ideal level 1 model with G = 5000V/V, ri = inf, ro = 0 How would I obtain the feedback function? Homework Equations I know I have to find the feedback function which is: f = - (ΔV/Vin) The Attempt at a Solution I will first drive using the...
  20. Boltzman Oscillation

    Engineering Derive expressions for the voltage gain of this opamp circuit

    Homework Statement Derive the expressions for the voltage gain (Gv) of the following op amp: Homework Equations In = Ip = 0 Vp =VnThe Attempt at a Solution I can use KCL, and the fact that In and Ip are both 0, to derive the two equations, one from the top node and the other from the...
  21. Shaq Melbourne

    Engineering LabVIEW Opamp Circuit Homework Solution with USB6008 Measurements

    Homework Statement The task States to build the I-V characteristic circuit where AIa and AIb are floating source measurements taken with the USB6008 and VS is supplied by the voltage follower circuit. I've also attached the actual script, for added context. Homework EquationsThe Attempt at a...

    How can I plot a graph for these opamp results?

    i have build and simulated the op amp circuit, i have recorded the voltage gain at different frequencies, now i need to plot a graph for the two results in same graph paper, i have not plotted a graph before for the related task so i need to understand from the basics, i need some one to...
  23. A

    Iref extraction in active power filters using active filters

    i was doing a research on active power filters and i read about Iref ( the cancelation waveform) extraction algorithm, and they are using complicated algorithms like FFT or DFT in frequency domain or the park transform and clark transform in time domain, i was wondering, why isn't there any...
  24. E

    Engineering Opamp Circuit Q: Find Vo in Terms of Vs | Chegg.com

    Homework Statement http://www.chegg.com/homework-help/questions-and-answers/ideal-opamp-find-v0-terms-vs-need-help-solving-vp-firstly-understanding-parts-q8278769 Homework Equations I am having difficulties with this problem. It asks to find vo in terms of vs. For the gain, I got an...
  25. adamaero

    OpAmp general rules-of-thumb (educated guess) on filter type

    Homework Statement For example, what type of filter is this: How can one tell, as a general guideline, without finding the transfer function? I think finding the transfer function is the only real way to tell for sure, but what is a quick way to make an educated guess? The Attempt at a...
  26. rishi kesh

    How does an opamp work as non-inverting amplifier

    Homework Statement I am doing a little bit of research about op amps. What i know so far from the book it that op amp have a very large open loop gain. To reduce the gain to desired amount we need resistor which connect output to invering terminal(negative feedback). Homework...
  27. ace130

    Analyze this opamp active filter circuit

    Hello, so this the circuit of an IdeaI OPAMP. The Question is to find the function Vs/Ve . I tried to make some sum ups to simplify it but I still unable to find a solution, so I tried to NOT sum up any component and found this: E-S=iZ+i2(Z+R) E=iZ+i3R S=i2R so the idea is to find E=f(i2) ...
  28. ace130

    Find S/E in Filtres & OPAMP Circuits: A Complex Schema

    So this is the circuit of a filtre and it's complex schema : The question was find the fonction S/E .In order to find S/E , I had to sum up impedances in serie or parallel, for example R2 and Z2 have the same current so we put R2+Z2=Z', but can I sum Z1+Z' ? since they have different current...
  29. J

    Opamp Doesn't Satisfy Ohm's law

    Homework Statement Homework Equations No current enters of leaves Opamp Terminals The Attempt at a Solution Red line is current path. Inverting terminal of Opamp -1 is at ground due to virtual ground concept, so Current = 2/1 = 2mA. This current goes through feedback path and then right...
  30. Pushoam

    Output voltage and output current of an Opamp

    Homework Statement Homework EquationsThe Attempt at a Solution Output voltage and output current of an OP-Amp Taking the OP-Amp as an ideal OP-Amp, the voltage at terminal 1 is 0 with respect to ground. The voltage at B is ## V_B = - 0.5 V ## ## i_{in} ## is from A to B. There is...
  31. M

    What is an opamp that is suitable for designing a sensor?

    I am finding a dual supply op-amp which has rate of voltage dropping to be low , input resistance is high about 30 -100MOhm and input offset voltage is low. All of them serve me to design a sensor that is pH sensor. Can you give me some your ideas for choosing ? Thank you !
  32. PhysKid45

    Opamp Voltages: Finding Output Voltage with Inverting and Non-Inverting Amps

    Homework Statement There are unknown values for input voltage, but we know it is sinusoidal. There is an inverting amp connected in parallel with a non inverting amp. The goal is to find the output voltage. I have three questions. 1: if the problem states that "power rails for both opamps are...
  33. M

    Dropping voltage at output of opamp

    Homework Statement I have problem at output of the first opamp . About 3 -4 minutes , the opamp's output voltage decreases by 0.1V . Although I reduced gain of opamp to 2, but the opamp 's output was still reducing 0.1V about 3 -4 minutes . Homework EquationsThe Attempt at a Solution
  34. W

    Suitable Opamp for this Low Pass Filter

    Homework Statement [/B] Select (with justification) from the op-amps listed in TABLE A those which are NOT suitable for use as the active component in the filter of (a) above. Homework EquationsThe Attempt at a Solution Currently The only Op amp I see that is not suitable is TLV2721 due to...
  35. J

    Why is the opamp output a voltage?

    Take the following circuit: The transistor turns the voltage input into a proportional current. Then it is said the resistor Rd turns the current back into a voltage. Then to calculate the output impedance of this circuit you would take Rd in parallel with the transisor's r0. But If you...
  36. A

    Find V(o) / V(s) in Output Opamp Voltage

    Homework Statement In the figure below find V(o) / V(s) Homework Equations In an opamp current doesn't enter through the inverting and non-inverting terminals, furthermore in DC conditions a capacitor acts like an open circuit The Attempt at a Solution The way I see it, both capacitors will...
  37. B

    Opamp Circuit: Finding Voltage at Resistor and Power Supplied

    Homework Statement Homework Equations V_- = V_+ The Attempt at a Solution There is negative feed back so V- =V+ ... Vout is then equal to the voltage at the positive terminal So the solution does a voltage divider... finding the voltage at the 4.62 ohm resistor.. However I did KCL at...
  38. K

    Opamp for MF/RF ranges (1.0-1.2MHz)

    Hello! I have a bit of trouble finding general op-amps that can amplify at medium frequency ranges, and with a good enough gain of 200 or 46dB. My max desired operating frequency is around 1.2MHz so I don't really care if it no longer amplifies much at frequencies higher than this. I am aware...
  39. T

    Opamp multivibrator not oscillating

    I'm trying to simulate this circuit in multisim The frequency should be 200 kHz. Used this site to calculate R1 and C1, http://www.electronics-tutorials.ws/opamp/op-amp-multivibrator.html All I get is this from the oscilloscope Is the circuit wrong ? or is it just the simulator
  40. Cocoleia

    Network function for an opamp circuit

    Homework Statement Homework EquationsThe Attempt at a Solution I'm really unsure of what to do. I feel like Vs should not be equal to Vo. I am not sure if I have the right idea with the equations that I have written. I am confused because I don't know the value for omega. Can someone help...
  41. Helmholtzerton

    Fully differential opamp for impedance matching

    Hello, I'm trying to get some feedback on my circuit design (picture below). I am attempting to use a differential op amp to impedance match a 100 ohm transmission line. The transmission line is CAT6A twisted pair. I'm using CAT6A as a feed through into a vacuum chamber. The design is to...
  42. F

    Op Amp Circuit Dilemmas: Diodes, Current, and Resistors Explained

    Q1. Why do we connect the Diode 2 in the Op Amp- Relay Circuits? (Check the image ) Q2. Why shouldn't a high current pass through an Op Amp? Q3. Why should there be a resistor in between an LED and an Op Amp output?
  43. whatphysics

    Unsure of finding Vout for this Opamp

    Hi there, these aren't homework questions. I came across them during revision and couldn't solve them. So any help would be appreciated. The ans for the 1st image is 2 and second image is 3. For the first image, I attempted to calculate the Req for 10k and 20k resistors connected to V1 since...
  44. Nikhil N

    Opamp as amplifier: Not getting the desired gain

    I want to amplify my input AC,50Hz to 30 times. I just started to test the basic inverting amplifier, with R2=4.7K and R1=1K. I varied the Vpp from 1 to 5 and I observed, I am not getting the gain of 4.7. Why this is happening ? One more doubt that I have is I used 12V Vcc, so if the input is...
  45. D

    Would an Opamp work wired up like this?

    I am trying to measure the voltage out of this dc-dc converter and am wondering if this method would work. The ground center point of the op amp bias is not the same reference as the return for the dc-dc output. Thanks for any help
  46. Cocoleia

    Is Vb 0V in this Op-Amp circuit?

    Homework Statement I am wondering if in this circuit Vb will be 0V? Homework EquationsThe Attempt at a Solution I have found all the other ones, but I am unsure if Vb will be 0 or not, and if it is then what is the logic behind it?
  47. D

    Transfer function question opamp + voltage divider

    〖 mod note: moved from technical forum, so template is missing 〗 〖 mod note: click on thumbprint image to see legible image 〗 I was wondering if anyone could provide some more insight as to how to find the current through Rc. The first picture TRANSFER1 I can find the current Ic through Rc...
  48. A

    Thevenin resistance in an opamp RC circuit

    Homework Statement In the figure given what is the Thevenin resistance between the nodes of the capacitor?? Homework Equations The Thevenin resistance is the open node resistance between two points. The Attempt at a Solution The way I see it, R2, Rf and R1 are in series and that combination...
  49. A

    Opamp RC-circuit -- Capacitor time constant calculation

    Homework Statement for the opamp circuit give in the figure, find Vo(t) for t > 0 the figure is attached. Homework Equations I know that tau = R * C that is the time constant of a capacitor discharging is equal to the product of the resistor that it discharges through and its capacitance.The...
  50. P

    A question about an opamp or comparator application

    hello dears i have a question at op amp could i use the comparator to compare between to differential signals .. more specific if i have tow signals out of phase (180) and unequal amplitude could i use op amp comparator or differential amplifier to distinguish which of them is higher amplitude ??