What is Op amps: Definition and 33 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. U

    How to Calculate the Complex Op Amp in Circuit Diagram

    TL;DR Summary: How to calculate the operational amplifiers in the circuit diagram Hello Everyone, I am trying to learn the circuit diagram of one of a device in which I will be doing modifications as a part of my Masters's Research to make it performance better. My background is in Mechanical...
  2. 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)
  3. altruan23

    Engineering Op amp circuit -- Did I calculate the output voltage correctly?

    can someone check, if i calculated the output voltage correct? i used virtual ground because V+-input of the op amp is 0 --> V- input is then also 0.
  4. C

    How do rail-to-rail op amps get so close to the rail voltages?

    I'm just curious, I have looked for application notes and such but don't see a simple answer to this question. Given the band gap of semiconductors that are very obvious in devices like diodes and transistors and such, how do designers achieve 'rail-to-rail' performance in an op amp, and get...
  5. R

    Engineering Find Vout as a function of V1 and V2 (OP Amps)

    Here's the circuit in question: Solution: Now, when I try simulating in LTSpice, this is what I get: So, Vout appears to be around -13 V, which doesn't agree with the equation if V1=V2= 5 is plugged in. Does anyone see the mistake here? THanks.
  6. 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...
  7. R

    Looking for a quad rail-to-rail op amp similar to TL074 in DIP14 package?

    Hello. I'm looking for a quad op amp similar to TL074 but rail to rail (mainly for input) in DIP14 (I found a lot in SMD) and supporting +12V / -12V as power supply.
  8. W

    Third Order High Pass Filter (Report)

    Homework Statement [/B] The filters of FIGURE 4(a) to (c) where designed using a commercial software package (http://focus.ti.com/docs/toolsw/folders/print/filterpro.html) Write a report (of approximately 750 words) that discusses and compares the design of each filter in terms of their...
  9. whatphysics

    Finding closed loop gain and Ip and In current in op amp

    Homework Statement Finding closed loop gain and Ip and In current in op amp Homework Equations - The Attempt at a Solution I started by trying getting voltage divider for points between R1 and R2 as (R2/(R2+R1))Vs and between R4 and R5 similarly. And I'm not sure how to continue on. Any help...
  10. whatphysics

    Finding closed loop gain in ideal op amp

    Hello there, this isn't necessarily a homework question. I came across this qn during revision and didn't know how to solve it. Any help would be greatyly appreciated. The answer is 0.97 1. Homework Statement For the ideal OP-Amp in negative feedback configuration shown in Figure Q30...
  11. K

    Inverting a signal up to 100mV using op amps

    Greetings, I'd like to invert a signal I get from a photodetector (the signals are up to 100 mV). I decided to use an inverting op amp circuit for that, however, when looking online through the op amp catalogs - the minimum input voltage in the descriptions is a few volts while my input would...
  12. B

    Impossible Op-Amp Circuit....Maybe

    Could anyone verify if this is an impossible circuit, I put it in pSpice and it didn't work, I have no op-amps or voltage generators to build the circuit otherwise I would have built it. What do you all think, is it possible to find the transfer function of the far right op-amp? The schematic is...
  13. Aristotle

    Am I on the right track in solving this OpAmp problem?

    Homework Statement Homework Equations H(s)= Vo / Vi Ideal op amp: V+ = V- Vo = V- The Attempt at a Solution To simplify the circuit, I noticed that the 200 ohm resistor and 60 microFarad capacitor are in parallel so: Zp = (R/sC) / [(1+sRC)/(sC)] = R / [(1+sRC)] Seeing that the Zp is in...
  14. kostoglotov

    How would you compartmentalize this circuit?

    This is not directly a homework question, as I found the answer. The question did not specify that compartmentalization be used, but it was in the section of Cascaded Op Amps, and the general idea of the section is to compartmentalize such complex looking circuits into cascaded stages of...
  15. 1

    OP Amp Comparators: V+ > V- for +16V Output

    Homework Statement https://physicsforums-bernhardtmediall.netdna-ssl.com/data/attachments/73/73750-4bf3d2aa03a724fcf0b13a6b1111902f.jpg The Attempt at a Solution V+ > V- for Vout to be +16V V+ < V- for Vout to be -16V V+ = -8x(in) V- = (-15x18)/30 + (15x12)/30 = -3 My attempt on it was that...
  16. R

    Fixed Gain Op Amps | Pre-Set Resistance for Voltage Boost

    Are there any readily available op amps with built in resistors that give a fixed gain, say 5, 10, 50, 100 etc. A lot of times I need to boost a sensor output and I'm too lazy to find/solder resistors do it. I'd rather buy a bunch of pre-set amplifiers that are ready to be plugged in and...
  17. A

    Can differential op amps operate without any supply?

    Just want to amplify the difference of inputs.
  18. T

    Question about bistable multivibrator op amps

    Homework Statement So for one of my labs, I had to make a bistable multivibrator and observe the transfer characteristics. The circuit is setup as follows: http://i.imgur.com/1G4M7DE.jpg (Image is too big to be inserted in this forum) This resulted in the following hysteresis loop...
  19. R

    Adjusting Op Amps for LED Lighting: Understanding Comparator Behavior

    Edit: I solved it, and found that it should be 30v because that causes a 24v drop across 40kohm resistor which is 6v, which is equal to the voltage at the non inverting terminal, meaning Vout will be +VSat, but I don't understand why this is correct, because my notes say that if the voltage at...
  20. T

    Question about bistable multivibrator op amps

    Homework Statement Here is the problem: So this is a bistable multivibrator. Homework Equations KVL and KCL lawsThe Attempt at a Solution I don't entirely understand bistable multivibrators. I get what the solution is, the input voltage caps at 0.1V and the output caps at 0.7V and hysteresis...
  21. A

    Can you boost RF signal power with a generic op amp?

    Sorry if this seems like a simple question, but I am new to RF systems. Is there a difference between an RF amplifer and a single rail operational amplifer? Or can you boost the power of an RF signal with a generic op amp? Also, when dealing with an RF signal, are coax cables and SMA...
  22. K

    Op amps, negative feedback or not?

    Homework Statement What is the exact definition of negative feedback? the instructor told us that negative exists if the output is connected back to the inverting input through a passive element. But what exactly is precise the definition ? (say parallel connect, same two nodes, I want the...
  23. N

    Slew-rate of Op Amps in practice

    Homework Statement We have a given op-amp, the data sheet has a specified slew-rate value for it, but in practice it happens to be a lot lower. I essentially used a step-input to determine the slew-rate and found it to be much lower. I can't remember the exact values now. I think The...
  24. L

    Two questions about op amps I've troubled for some time.

    Hi, I was hoping someone could help me resolve a little difficulty I have. ------ Question number one: Say you have an op amp with a negative feedback. I've been taught that the principle of 'virtual ground' must hold. But what happens for a circuit for like this? As you can see, I...
  25. D

    Cascading low pass op amps, derive expression for f3db

    Homework Statement consider the cascading of two non identical amplifiers stages, each having a low-pass STC frequency response. STage 1 has a low freqency gain of ALF1 and a 3 dB frequency of f1. Stage 2 has a low frequency gain of ALF2 and a 3 dB frequency of f2. Derive a polynomial...
  26. R

    Understanding Op Amps and Kirchoff's Current Law

    Hi I was starting to read up on Op Amps and near the beginning they said that current flowing into an Op Amp equals current going out (output current + 2 input current + 2 source current = 0) on the basis of KCL. I'm confused because I thought KCL only applied for all currents entering and...
  27. S

    Questions about RLC circuits and OP amps

    Hi guys I really need some help to finish this on time, 1. A circuit with V volts and a 2 ohm resistor and a 2mH inductor and a 500uF capacitor in series. There is a graph of current through circuit over time, starting at 0 current icnreases to 20 amps in 1 mS stays there for 1 ms then goes...
  28. G

    Integrator Design for Acceleration of Falling Object | Op Amps Homework Solution

    Homework Statement Hi! I've to try and solve "use two opamp integrators to solve the differental acceleration of an object falling under the force of gravity d^2y/dt^2 = 10" Homework Equations Vout = -1/Rc * integral (Vin dt) The Attempt at a Solution I'm really stuck as to...
  29. B

    Electrical Engineering Op Amps Problem

    Homework Statement http://i8.photobucket.com/albums/a45/bahester9/opamps1.jpg Homework Equations I know I can use KCL to solve at a node if I was looking for like a voltage. But I'm not sure really about the current, Ix. The Attempt at a Solution I know that Ix has to somehow be...
  30. E

    Understanding Input Offset Voltage in Real-World Op Amps

    hi I've been set a project to test the limitations of the ideal op amp when applied to the real ones, and its doing my head in, if any of you could help me figure this one out i'd be very thankful. the first thing I'm confused about is the input offset voltage: i know its the voltage...
  31. E

    How Do You Calculate Transfer Functions for Op Amp Circuits?

    I have a question regarding finding the transfer functions when dealing with op amps. I do not understand the steps towards going from a general op amp circuit towards getting an the transfer function where you can draw the bode plots for magnitude and phase. Could anyone give me a general...
  32. P

    Can Op Amps be Used for Digital Circuits?

    I had electronics last semester, and we went over some digital briefly at the end. I think we learned a bit about digital circuits using diodes and something about transitor-transitor logic? Anyway, at the time I was wondering if there was a way to use Op Amps to create digital circuits.
  33. B

    What is the purpose of Op amps

    hi, i'm a little...a lot confused about op amps. in english, can someone tell me their purpose? thanks