What is Op-amp: Definition and 217 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. DIYEngine235

    Amplifier Circuit help, impedance matching

    I've been working on a personal project to connect my old H10 series david-clark headset to my UV-5R radio. Up to this point, I've been using the headset purely as a set of headphones to listen in, but I want to be able to transmit with it as well. The problem I'm running into is that the...
  2. E

    Stability test for Feedback Amplifiers

    Does the following simple test deduced from Nyquist criterion also apply to positive feedback or it needs to be modified? If magnitude of loop gain i.e. |T (jω)| > 1 at the frequency where phase(T (jω))= −180◦, then the amplifier is unstable. Reference: Analysis and Design of Analog...
  3. Callicious

    Op-amp compensation of cascade fudges audio signal oddly

    Links: LTSpice Pre-amp schematic (resistor values/capacitor values different) Gerber Op-amp Datasheet Hi all; Presently designing pre-amp for my analogue MEMS microphone for bioacoustic recording (ultrasonic, especially.) Don't own an oscilloscope, so relying on spectrograms of audio for...
  4. Wrichik Basu

    Any advice to make this Op-Amp temperature controller circuit work?

    As part of our UG curricula in Physics major, we have a practical in which we have to draw the calibration curve of an NTC ##10~\mathrm{\Omega}## thermistor, and then construct a circuit to maintain the temperature of a water bath. The calibration curve of our thermistor. The Prof. said that...
  5. DenDanne

    Calculating the voltage in an OP-amp circuit with a current source

    Summary:: Find the voltage in an OP-amp circuit with current source I(in) = 1 uA. What I'm confused about is if there is any voltage flowing through R1. Because if there was and let's say it went downwards, then where would it go, I mean it cannot just disappear. And if it goes upwards...
  6. ergospherical

    Justifying the peak closed loop gain of an op-amp circuit

    I'm just looking at a Bode plot of log(gain) vs log(frequency) for a an amplifier circuit. I'm trying to figure out whether I'm expecting to see a resonance in the gain at the frequency where I measured one. How could I, in principle, work out theoretically where the peak gain should occur - is...
  7. P

    Engineering Proportional only controller in LED Driver using Op-Amp

    I have a proportional-only controller LED driver circuit - I need to fine-tune its ##K_P## to 10 for a significant input of -0.2 to 0.2 V in the steady state. In that case, should I use a potentiometer with 10:1 setting? The LED (actuator) can drive voltages between 0 to 4V, so I need to add...
  8. 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?
  9. P

    Engineering Analyzing the output impedance and open loop gain of a IC-741 Op-Amp

    Here is the internal circuit of the 741 Op-Amp - Looking at the output stage, the output impedance seems to be the series combination of ##25 \Omega## and ##50 \Omega##, that is ##75 \Omega##. Is this a qualitative explanation enough to justify the output impedance, or am I wrong somewhere and...
  10. P

    Engineering Analyzing the internal circuitry of IC 741 Op-Amp step by step

    Here is the internal circuit of a 741 op-amp - Here is a HSpice model I found in the educational section - Both are essentially the same, keeping aside subtle differences. I am yet to understand the technicalities of an op-amp, so I would like to analyze the circuit using the first picture...
  11. Callum Plunkett

    Inverting Op-amp signals and Sawtooth waveform generation

    I’ve been asked to create a sawtooth wave form with four input voltages. After doing this I then added a second op-amp to both change the range of the wave form from -/+5v to -/+2.5 and DC offset of 2.5v to create a wave form that ranges from 0v – 5v as required by the question. For the most...
  12. Wrichik Basu

    What's wrong in my LTspice simulation of an Op-Amp integrator circuit?

    I am doing an online course on op-amps. The specific video I am talking about is this one (skip to 24:25). Here, the professor has derived the expression of the op-amp integrator circuit, and in the next slide, he tells that we can create a triangular wave from a square wave using this...
  13. PRITAM the cat of Ne

    Engineering Op-Amp circuit output analysis trouble

    THE ANSWER IS GIVEN: 6V, but according to me as the positive terminal is grounded the negative terminal will be virtually grounded (0V), from ohm's law (applying to the two series resistance) it is expected that Vo is 0V! I don't know where I am getting wrong!
  14. hugo_faurand

    Amplifier for piezoelectric sensor, OP Amp circuit

    Hello everyone ! I'm working with a piezoelectric cell and I need to retrieve the variation of the charge of the cell as a voltage signal. I found this circuit (a charge amplifier) with an OP Amp ( here the piezo cell is represented as the current source with the capacitor and the resistor on...
  15. M

    I Checking for negative feedback in a circuit

    This is the circuit in question. During lecture, when checking whether this was negative feedback, my instructor said that if the v_out increases, then v- increases as well, which would lead to the next v_out decreasing because v_out = A(v+ - v-). I get how if v- increases the next v_out would...
  16. F

    Simulating op-amp circuits using Multisim/Matlab

    I tried to simulate the circuit shown in fig 1 using Multisim and here's my work: The result: I do not know where is my mistake, could someone help me figuring out the problem? Any help would be greatly appreciated!
  17. P

    Engineering Calculating the unknown voltages in ideal op-amp circuits

    Hi - I have made an attempt at both of these circuits, but I am not 100% sure I am correct. Would it be possible to check if I have this right, and if not, please give me some pointers as to where I have gone wrong? Thanks First op-amp Given data: Vo = 5V I have called the voltage feeding into...
  18. bornofflame

    Engineering Using KCL on this Op-Amp circuit to solve for V0 and I0

    Another classmate and a web search show that the answers for this problem are v0 = -12 V, and i0 = 2.4 mA. This was done using KVL around the circuit. I should be able to reach the same answer using KCL but I haven't and I'm not sure why. Is it because the source isn't connected to ground and so...
  19. T

    Op-amp Oscillator Circuit Design (10-50 MHz)

    Questions: 1. Is LM741 capable of oscillating at 10MHz? If not, could you suggest me an affordable op-amp for this operation? 2. How likely am I, as a beginner to be able to design a zero phase shift feedback filter to use with a non-inverting op-amp circuit to create an oscillator? 3. If an...
  20. Kaguro

    I Understanding Op-Amp negative feedback

    In an op-amp with negative feedback, say initially the + input has some small positive value and the - input is at 0. Then the op-amp amplifies this difference, and a part of it is fed to the - terminal through resistances. This will increase - and will lessen the difference. My question is...
  21. Z

    What are the limitations of using real transistors to build an ideal op-amp?

    What are the transistor characteristics and limitations from building an ideal op-amp?
  22. W

    Engineering Looking at Operational Transconductance Amplifier (OTA) Ibias and load

    My attempt at the OTA is as follows: The simulation circuit is as follows: I've gotten this far largely due the nature of the handout and its hints. I'm struggling with understanding ibias From my understanding, there is a current mirror at the top of the OTA. This creates an infinite input...
  23. paulmdrdo

    Engineering Does Zero Initial Energy Affect the Rate of Change in 2nd Order Op-Amp Outputs?

    I was reading about this 2nd order op-amp circuit which is essentially a cascaded integrator and got confused with the explanation of the book regarding the rate of change of the outputs. The book said that when the initial energy stored in the circuit is zero then this rate of change is zero...
  24. W

    Instrumentation op-amp problem

    Homework Statement Homework Equations [/B] CMRR = Av/Acm Acm= Δ/R , Δ = (2 x Tolerance of Resistor).R The Attempt at a Solution I have an issue with part e) and f) but here are all my workings c) For this part, Acm would be: 10 x10^-3 This makes 2.5mV -> 0.25 uV (which is the same...
  25. W

    Engineering Grounding Op-Amp circuit exercise

    Homework Statement 2. Homework Equations 3. The Attempt at a Solution For the first set of questions: I've worked through to part 6), at which is I encountered my first problem. I'm not entirely sure what the question is asking. Is it as if there would be a capacitor between...
  26. S

    Engineering Op-Amp Resistive Circuit Homework: Finding Vo in a Given Circuit

    Homework Statement The attached picture is the circuit I have been given and I am asked to find Vo (the voltage drop across the 6k resistor. Homework Equations v_out/v_in = (R_1 + R_2)/R_1 V+ = V- The Attempt at a Solution So I know that the voltage drop across the 6k resistor is just the...
  27. eigenmax

    Help for interpreting Opamps on a schematic

    Hello, I've been doing electronics for a while now, and only recently started using ICs. I have no problem with the 555 timer (I've used it in several circuits), but recently found and attempted the construction of a few circuits with the LM358 op-amp. On each there were two triangles, which I...
  28. paulmdrdo

    Engineering Op-Amp Circuit Analysis: Troubleshooting Incorrect Node Usage

    In the problem below, when I use nodes V1 and V2 I get the correct answer of Vo = -2.5v But when I use nodes V1 and Vo I get an incorrect answer. Please explain to me why my latter method did not work. Thanks.
  29. C

    Understanding the Ideal Op-Amp Negative Feedback Loop

    Homework Statement Hi, Here is what I know about the Ideal Op-Amp. - The open loop voltage gain is infinite - The output voltage is given by the following $$v_o = A(v_+ - v_-)$$ - Only with a negative feedback loop is $$ v_+ = v_-$$ My query is with regards to the negative feedback loop...
  30. jSwathi

    Cascaded op-amp stages and saturation of final stage

    <Moderator's note: Thread split from another thread as the posts essentially comprise a new question about a new circuit. The problem statement has been formed by combining two of the moved posts. Poster has been notified to create a new thread for a new question> 1. Homework Statement I am...
  31. genxium

    Does Wien bridge oscillator have a closed-loop gain?

    Homework Statement By Wien bridge oscillator (abbreviated as WBO below) I refer to this circuit where the op-amp is assumed to be ideal and the output is the voltage drained from the upper end of R3. What confuses me is that I hardly find a reference which explicitly states that a WBO has a...
  32. C

    Ideal Op Amp HW: KCL, V/R, V+ = V-

    Homework Statement Homework Equations [/B] KCL I = V/R V+ = V- (ideal op amp)The Attempt at a Solution [/B] I really don't think my voltages for ia and ib are correct. I am just not sure how to use the V- = 4V in those some how?
  33. C

    Ideal Op-Amp Voltage sign error

    Homework Statement Above is my attempt of the answer and the problem q. The correct answer is -2V. In the solutions given to us, it has this line: I understand that V- is 0V due to the characterisitcs of an op-amp. But I don't understand where is the - V0 coming from. Any ideas...
  34. adamaero

    Predicting AC open-loop gain for an internally compensated op-amp

    Homework Statement An internally compensated op amp has a DC open-loop gain of 1,000,000 (V/V) and an ac open-loop gain of 40dB at 10kHz. Provide the expected gain in dB at 1kHz... Homework Equations Please help, I don't know what to use for an exact answer. The Attempt at a Solution Beyond...
  35. G

    Op-amp circuits and noise at high frequency/low amplitude

    Hi everyone. I am tasked with amplifying an input voltage of around 1nA at anywhere between 10,000kHz to 1MHz to a sufficient amount. We've been using op-amps in multiple stages in series to amplify the signal. At our disposal we have a function generator, oscilloscope, breadboard and...
  36. T

    Engineering Op-Amp circuit with applied external compensation

    Homework Statement FIGURE 3(b) shows the THS4021 in a practical op-amp circuit with applied external compensation. Determine an expression for the low frequency gain of the circuit. Homework EquationsThe Attempt at a Solution I really don't know where to start. Is there a virtual Earth at the...
  37. T

    Comparing Op-Amp Parameters: Ideal vs A & B

    Homework Statement 1. a) Contrast the relative performance of each op-amp in terms of these parameters and state how they compare to that of the ideal op-amp. b) TABLE B gives two descriptions of operational amplifiers. State, with justifications, which description most closely matches the...
  38. I

    Understanding Op-Amps: Analyzing Circuits and Exploring their Functions

    Hello again, Physics Forums. I was studying this op-amp (no its not homework) and I am not sure if i am analyzing it correctly or not. So far that is what I have. I was also wondering what the purpose of these highlighted sections are: The RL circuits look like filters, but I don't quite...
  39. T

    How Can an Op-Amp and Diode be Used to Convert 12V to 5V for a PIR Detector?

    Homework Statement FIGURE 3 (on page 7) shows a PIR (passive infra-red) detector and its associated amplifier, as used in burglar alarm systems1. (a) The detector is powered from a 12 V unregulated supply that needs to be stepped down to 5 V. Design a suitable 12-to-5 V voltage converter using...
  40. K

    Zero phase shift Op-Amp bandpass filter design

    Homework Statement "design a band pass circuit having a midband gain of 20 dB with -3 dB frequencies at 20 Hz and 20 KHz the amplifier should not produce any phase shift." does midband gain strictly apply to voltage gain (because that's how i look at it)? I was going to use a common collector...
  41. 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...
  42. G

    Effect on the output using a TL 072 op-amp

    Homework Statement Replace the ideal op-amp by the TL 072 [the default op-amp] and note the effect upon the output. Can you explain it? Homework Equations The Attempt at a Solution i can see there is a large spike on the output volts of the trans-impedance op-amp using the TL 072 op-amp...
  43. G

    Calculating Input Voltage for Switched Op-Amp Circuit

    Homework Statement Calculate the input voltage to an Op-Amp circuit. The circuit is exactly an ideal non-inverting amplifier except the inputs have been switched in that the supply is connected to the inverting input and the middle of the potential divider is connected to the non-inverting...
  44. T

    How does an Op-Amp "find" equilibrium (w/ Negative Feedback)?

    Hi everyone, I've been seeking the answer to this question for a long time. I've looked at posts like... https://www.physicsforums.com/threads/op-amp-transient-state.855512/ and https://www.physicsforums.com/threads/how-does-negative-feedback-in-an-op-amp-work-conceptually.584881/ ...but I...
  45. K

    How does negative feedback affect op-amp response?

    Hello, I have two questions about feedback. 1. If we look at the equation above, it says G(Vin-BVout)=Vout but this equation is actually,G(Vin-BVout1)=Vout2 whereas Vout1 is Vout for first iteration and Vout2 is Vout for 2nd iteration. Therefore, they must have different values. How can we...
  46. A

    Help designing a music visualizer for a 12x12 LED screen

    I am working in a group for designing a LED interactive Screen. My part of the project is the design of the music visualization system. I am new in this area, but I know I need to use some op-amps to filter the input signal from the mp3 player. Could anyone give me any suggestions on how to...
  47. bombo

    [help] understanding Op-Amp frequency characteristics

    Hi I need help understanding the frequency characteristics of operational amplifiers. I do not understand why the output of an Op-Amp behaves much differently when the frequency of the input is increased. For example during the lab when the input to an inverting Op-Amp circuit was a sine...
  48. R

    Schmidt Trigger Help: OP07 Comparator Circuit Design

    I have been been trying to search forums and figure out the following question that I just cannot seem to get my head around! Design a Schmidt comparator circuit based on an OP07 operational amplifier with the following characteristics: Power supply Voltages: +/- 12V Switching thresholds +1V...
  49. G

    Why resistor between +input and ground necessary in OP-AMP?

    Hello. Please see the attached image first. 1. The textbook seems say resistor to + input in this image is necessary to provide a return path to ground. I completely don't understand even what it mean. Could you help me to clarify this? 2. Instead of understanding directly what the book said...
  50. G

    Question for stability of negative feedback OP-AMP

    Hello. I've studied the golden rules of the feedback OP-AMP and applying this to voltage follower shows that voltage gain (Vout/Vin) is 1. Thus, Vout should eventually follows Vin when Vin suddenly changed. I've tried to follow this process for clear feeling by drawing pictures as shown in the...