op-amp Definition and Topics - 18 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. 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...
  2. 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!
  3. 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...
  4. 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...
  5. 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...
  6. 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...
  7. 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...
  8. 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...
  9. 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...
  10. R

    Schmidt trigger help

    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...
  11. ichabodgrant

    Op-amp as a comparator (analog-to-digital conversion)

    Homework Statement Okay, This time it's an exam question. I am doing some past papers and there are questions about comparators which are not introduced in this course (this course is preliminary course for engineering students who are interested in electrical, electronic or computer...
  12. D

    Using analog computer to solve 2nd-order diff eq

    I'm trying to build a circuit to solve the differential equation x''+2x'+x = f(t), where f(t) is a sine wave with frequency 5Hz and amplitude 0.5V. I am supposed to get a sine/cosine wave (as the diff. eq is just the same as the ove governing spring-mass forced oscillation) as solution, but...
  13. D

    Adding resistors to a differentiating op-amp?

    I know how to derive the expression Vout = -CR*d(Vin)/dt for a circuit differentiator that consists of a capacitor and a resistor, how I can understand the attached circuit, which is part of practice exercise for my class. Why do we need to add R2 and R3? When I run the simulation Vout =...
  14. ichabodgrant

    Engineering Op-amp circuit analysis 2

    Hi. I have moved on to the next question. There is something I am confused. The question wants us to express Rf in terms of R such that vo = -15vi. After doing the last task, I think I understand the flow of solving it. But here still exists a problem. My attempts and question are listed in...
  15. ichabodgrant

    Engineering Op-amp circuit analysis

    In the following circuit, compute the values of R1 and R3 in terms of R2 and R4, such that vo is always equal to v1 - 5v2. I have marked 3 nodes, A, B and C. v+ = v- as assumption for the op-amp. Consider node A. v- = v+ = v1 × (R2 / (R1+R2)) Consider node B and C. (v- - v2) / R3 = (vo -...
  16. J

    Ideal opamp analysis

    Given this ideal op-amp, determine Vout if Vin = 2V and Vs = 15 V. So I know that the ideal op-amp has infinite gain. As the difference between V+ and V- is substantial (2V), wouldn't that mean the output would theoretically by infinitely large but instead max out at Vs? Am I understanding...
  17. C

    Engineering Non Inverting Op-Amp Circuit Analysis

    Homework Statement For an input potential (Vin ) which is a 1V (peak) sinusoidal source. Calculate V1 and Vout Homework Equations - The laws for an op-amp - NVM The Attempt at a Solution Here is my attempt not sure if correct.
  18. H

    Photodiode Amplification

    I am using (attempting to at least) a photodiode to count fringes from a Michelson interferometer. Here is the amplification circuit I am using: Coming out of the op-amp into the comparator I get about 4.2V in a well lit room, 2.17V in total darkness, and 2.33V when the brightest part of the...
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