What is Op amp: Definition and 307 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. M

    Upper 3db Frequency of Op Amp Help

    So I did the first part, and got the gain as 11. I also did part c, and got approximately 80khz, but I'm not sure what to do for b). I know that at the 3db frequency, the voltage is at 1/20.5 of it's amplitude. So can I just use the equation f=(slew rate)/(2pi*A), and set A to 1V/20.5, and...
  2. W

    Engineering Op Amp Circuit Help: Solving KCL Eq with Source Transform

    It was much easier scanning the pictures and problem than trying to recreate: I began by doing a source transform, making Vs = is*Rs, and placing Rs in series instead of parallel. I then did KCL at Vn. I tried to break the KCL eq down to il/is, but just ended up with some un-godly...
  3. H

    Why is there resistor R2 connecting output and input of op amp?

    I have attached image. Thanks in advance.
  4. H

    What is the circuit desighn within op amp?

    I am first year student 0f electronics and communication engineering. I have a course called basic electronics. I have already learn't bjt,jfet,mosfet,diff amplifier etc, now its turn of op amp. And I can't move on without knowing what is within op amp. Pictures shows Triangle and +,- within...
  5. M

    How Is Capacitance Multiplied in an Op Amp Circuit?

    Homework Statement Please, I would like to know how to find the factor by which the capacitance is multiplied A picture of the Op Amp is here: http://en.wikipedia.org/wiki/File:Cap-mult-op.svg Zc is complex impedance of C Homework Equations none given The Attempt at a Solution...
  6. I

    What Is the Name of the Circuit Converting 4-20mA to 1-5V Using an Op Amp?

    I have found this circuit in my travels on the internet and it should suit my needs. I need to know what this configuration is called so I can calculate the resistors for the gain needed. If anyone knows of a similar circuit that has trimpots to adjust the 4mA to 1v and the 20mA t0 5v that...
  7. K

    Op Amp Voltage Limits: Protecting Your Circuit from Damage

    What will happen when the input voltages applied to the op amp is higher than its supplied voltage? Will it damage the op amp?
  8. S

    Amplifying WiFi Signal with an Op Amp: Is It Possible?

    could one attach an op amp to a wifi transmitter to amplify the signal? thanks.
  9. S

    Inverting OP AMP analysis solution problem

    Hello Physics Forums community, I'm a new member and this is my first post. I have a circuits exam tomorrow, and though I grasp the majority of the material I'm having a hard time understanding the solution to a HW problem that I attached as a picture. Problem: Show that the circuit has...
  10. Z

    Analysing Op Amp Circuit with a Photo diode

    For a lab we built the following circuit. Our photo diode was receiving a blinking signal which our op amp made visible on a DVM. I do not understand the purpose of the capacitors attached to the power rail. So far I understand how negative feed back with the Rf resistor controls the amount...
  11. N

    Ideal op amp (current to voltage converter + inverting)

    Homework Statement Hey there.. need helps here.. The question is.. Derive an expression relating the output voltage, Vo to the input current, Iin. The Attempt at a Solution i try to derive it.. but.. got problem with RL V1 = -IinRf Vo =- R2/R1(-IinRf) how to include Rl in my...
  12. N

    Design an OP AMP Power Supply for Audio Preamp

    Hello, I am trying to design a foundation for an audio preamp that is powered by a single 9V battery. I am successful so far except the single power supply part. I am using the voltage divider scheme to get a +4.5V and a -4.5V reference voltages. With no load the supply voltages are close to...
  13. N

    Single Op Amp as a voltage regulator?

    Hello all. I was just wondering if it is possible to use an inverting opamp configuration with feedback to regulate an output voltage V0 without the use of BJT's? For example, the following sketch: http://img411.imageshack.us/img411/2389/opamp.png V0 = Vs * (R1-R2) /2R1 Mathematically, V0...
  14. I

    Constant current source using an op amp

    I'm currently in the process of building a constant current source using an op amp. Circuit diagram: http://upload.wikimedia.org/wikipedia/en/9/97/Op-amp_current_source_with_pass_transistor.png I'm using a voltage reference instead of a zener diode. Currently the load resistance is 0...
  15. G

    Inverting op amp with positive input NOT grounded

    For an inverting op amp with the positive input grounded, the equation for V(out) is (Vin)*Rf/Rin. Thats fine But what if the positive input is not grounded? What if there is a voltage applied to that input as well? How would I find V(out) when the positive input voltage is larger than the...
  16. R

    Choosing an Op Amp for Circuit Triggering

    Dear experts, I am thinking of using an op amp to trigger a circuit. The +ve input to the op amp should raise '1' (high) if the voltage is 5v and not anything less. The -ve input to the op amp should always be '0' (low) and so i thin i short it to ground. I wonder what op amp should i...
  17. G

    Op amp bandwidth and gain problem

    Could sb explain to me how to calculate the 3db frequency of the inverting op amp, please? 1. For non-inverting op amp If Bandwidth gain product is 1.5x10^6 Hz and gain is 20dB then the F3db is given by Bandwidth gain product over 20. It equals 150kHz. 2. For inverting op amp the F3db is...
  18. W

    Finding R for Ideal Op Amp to Avoid Saturation

    Homework Statement if the op amp satuates at +-14v, determne te the range of values of risitance R for which the op amp does not saturate. Assume the op amp is idal Homework Equations V-=V+ The Attempt at a Solution this is wa i have so far: (2-5/3)+(2-+14/R). not sure if it is...
  19. D

    Understanding the Behavior of Inverting Op Amp Circuit with Switched Terminals

    please look at this circuit http://hyperphysics.phy-astr.gsu.edu/Hbase/Electronic/ietron/inva2.gif The transfer function for the the circuit above is Vout = (-Rf/Rs)*Vs if I were to switch the terminal of the op amp so that Vin is inputted into Vp and Vn =0 instead (everything is the same...
  20. M

    Op Amp Temp Drift: Minimizing Temperature Variations

    I'm using an opamp to amplify ac signals 40hz and up but there is still temperature drift, I thought drift was only a problem for dc signals? how do you get rid of temperature drift?
  21. A

    Interfierence with infinite gain op amp

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  22. R

    Cascading Op Amp: Practical Experience Needed

    Hello. I'm looking for someone having practical experience of cascading video amp like NE592 or LM733 in order to get wide bandwidth and huge gain.
  23. U

    What Components Make Up an Op Amp?

    What's inside an op amp? Is it just an npn transistor used for amplification? So can we explain it in the terms of base and collector current? Please elaborate simply (It's a high school project)
  24. R

    Op Amp built with discret components and having GBP over 30 MHz.

    Hello, for technical reasons I'm looking for a schematic of an Op Amp built with discret components and having GBP over 30 MHz.
  25. M

    Op Amp Current Supply - Is 3 Amps Too Much?

    Do opamps have current limit, I have an OP-27 dual supply connected to 2 9V batters the battery measures 3 Amps and 16 volts is this too much current?
  26. C

    Using 741C Op Amp with Vcc=+9v and Vee=0: Possible?

    If I run a 741C op amp with Vcc=+9v and Vee=0, will it affect the functioning of the op amp? Can I still use it as I normally would? For a 741C Vcc=|Vee|=13v.
  27. E

    Understanding Op Amp Offset Voltage: Rules & Examples

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  28. M

    OP07 Op Amp Output Unexpectedly High Voltage

    When I connect 3V negative and 3V postive power supply to an OP07 op amp and I Connect a voltmeter to OUT of op amp and GROUND the voltmeter shows -1.8 volts why? I have connected anything to input I even tried shoring the input and this voltage is too high to be offset voltage. I Tried two...
  29. A

    OP amp analysis help-exam paper question

    Homework Statement i have this exam paper question. derive an expression for transfer function find expression for the magnitude and phase of the response i have attached circuit diagram below 2. The attempt at a solution i derived for first question Vo= 2RC(dVi/dt) -...
  30. Mapes

    Choosing a capacitor for an op amp integrator

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  31. T

    Op Amp inverting amplifier , help

    http://i454.photobucket.com/albums/qq261/integralx2/opamp1.jpg I don't understand why they did something. I found output voltage to be -1.25v , but to find voltage across the 10k resistor, its (Va-Vo)/10k am i correct? cause when i do this and try to calculate the answer for Io its not right...
  32. P

    Op Amp Circuit Analysis Question: Transfer Function and Ideal Analysis

    Homework Statement G'day, the op-amp circuit is attached. Need to know the Transfer Function. Homework Equations Using Ideal analysis. In=Ip=0A, and Vn=Vp Vo/Vi=-15 The Attempt at a Solution I have had many attempts at it. Because We don't know the input current (no input...
  33. S

    Why do some op amps require capacitors in parallel with supply voltages?

    For the INA101, in the configuration for the most basic circuit with the TO-100 package, two 1 mircofarad capacitors seem to be required to be placed in parallel with the supply voltages. Why is this, and is it actually necessary for an operating circuit, since the circuit example with the Dip...
  34. I

    Circuits Op Amp R equilvalent help

    [SOLVED] Circuits Op Amp R equilvalent help! Homework Statement I'm working on Ideal op amps and I need to find the R equivalent of the system. I'm not sure if this term is used in other places but R equivalent = total Resistance of the circuit...
  35. I

    How Do You Calculate the Equivalent Resistance in an Op Amp Circuit?

    [SOLVED] Op Amp Requivalent Please help! Homework Statement I'm working on Ideal op amps and I need to find the R equivalent of the system. I'm not sure if this term is used in other places but R equivalent = total Resistance of the circuit. http://img169.imageshack.us/img169/4386/reqrk6.png...
  36. J

    Inductor as a differentiator (op amp)

    Homework Statement Sorry this computer doesn't have access to PSPICE and I don't have a scanner, but let's say that I have an op amp. 1) there is a time varying voltage source Vs 2) There is a resistor R1 connected to the inverting input of the op amp 3) The noninverting pin is connected...
  37. F

    Engineering Solution to Op Amp Circuit Problem: R1=R2=R3=R5=R

    Homework Statement For the following circuit, sketch v2/v1 as a function of R4, if R1=R2=R3=R5=R. Also explain the behaviour of the circuit when R4=R/2. Homework Equations The Attempt at a Solution After solving the circuit, i came up with v2/v1=2R4/(2R4-R). Now, if R4=R/2 ...
  38. F

    Engineering Solve Op Amp Circuit Problem: Find V2/V1 w/Potentiometer

    Homework Statement The op amp circuit shown bellow is intended to provide any gain between -10 (for k=0) and +10 (for k=1) by adjusting the potentiometer. Let R1 and R2 have the scaled values, show that.. V2/V1= {r1/(r1+10k)} [-11/{1+(10kr1/r1+10k)}] + [r2/r2+10(1-k)] [1+...
  39. E

    Can anyone recommend an integrator op amp?

    Hi, I'm building an integrator using an op-amp to integrate 15 volt 65nS pulses at a repetition rate of 100Khz using a 20uS time constant. Can anyone recommend a suitable op-amp for this application. It needs to have very low input bias current to minimise d.c. drift and have sufficient...
  40. M

    Yet another Op Amp question. Damn I hate these things

    For the circuit below, find Vx and Vo. http://www.freewebs.com/mushg/FWThumbnails/OpAmp.bmp
  41. M

    Understanding the Op Amp Minus Sign Symbol

    What does it mean when an op amp has only a minus sign in its symbol? Is the positive terminal at ground, or is it at some arbitrary voltage?
  42. E

    Determining CMRR for an op amp with two electrode inputs

    Homework Statement I have an op amp with two electrode inputs. Each input has 5V of common 60 Hz noise. The size of the signal I want to measure is 9 mV. Signal to noise ratio needs to be 10 to 1. Homework Equations I know that CMRR = 20 log (DMG/CMG), where DMG is differential mode...
  43. E

    Solving an Op Amp Circuit with Mathematica

    Here's my problem: Rs is a resistor whose value depends on temperature. Rs = R0 - 1.8T, where R0 = 5000 ohms and T is in Kelvin. If the ideal op amp has +/- 15 V power rails and you want to maximize the circuit's sensitivity, what should Rf be on the op amp? What is your maximum...
  44. V

    Second Order Op Amp circuit: Find Vo for t > 0

    Homework Statement In the circuit below, determine v_o(t) for t > 0. Let V_{IN}\,=\,u(t)\,V, R_!\,=\,R_2\,=\,10\,k\Omega, C_1\,=\,C_2\,=\,100\,\muF. http://img249.imageshack.us/img249/3840/problem867cg5.jpg Homework Equations i_c\,=\,C\,\frac{dv_c}{dt} The Attempt at a...
  45. S

    Engineering How Does Setting Rx to 60k Affect the Output Voltage in an Ideal Op Amp Circuit?

    1. http://img248.imageshack.us/img248/8971/opampanalysisxe2.png Assume that the op amp in the circuit shown is ideal. a.) Find the output voltage when the variable resistor Rx is set to 60k Assuming Ideal Op amp. All currents leaving nodes are negative. V+ = V- = 0 and In = Ip = 0...
  46. D

    Newbie Needs Op Amp Help on Homework Problem

    I'm new to op-amps, and would like some guidance. I have a quick question on this HW problem. I'm not asking you to do it for me, but I want to see if my hunch is correct: http://img66.imageshack.us/img66/8872/screenshot01bb7.jpg Now, using ideal op-amp model... I'm going to assume: V+ = V1...
  47. N

    Designing an Op-Amp with Variable Gain: Need Advice

    Homework Statement Design an op-amp that uses a variable 50k ohm resistor. when this variable resistor is at one extreme, the gain is 13, and at the other extreme, the gain is 3. you may use up to 2 op-amps, and up to 7 resistors (including the variable resistor) The Attempt at a Solution...
  48. B

    Op Amp Resources: Learn How to Calculate Output Voltage

    This may be kind of odd, but this is my first post, so I'm kinda new at this. I need to calculate the output voltage of an op amp with a 2 mA current source inputting into the inverting side, and a ground connected to the inverting input. There is a 1 kiloOhm resistor going across the op amp...
  49. R

    Finding V_o and i_o for an Ideal Op Amp Circuit with Multiple Unknowns

    Find V_o and i_o. Assume an ideal op amp. http://img236.imageshack.us/img236/2426/633bb0.jpg I tried applying KCL at v1 and v2 nodes but then got stuck because I had 2 equations with 3 unknowns. \frac{12-v_1}{4} = \frac{v_1-v_2}{8} and \frac{v_1-v_2}{8}+\frac{-10-v_2}{20}= i_o...
  50. M

    Combining Summing and Difference Op Amps: Troubleshooting v_+

    hey guys, i have a HW problem of a combination of a summing and difference op amp. I got the first few steps of the problem, but i don't know how to continue from where i am. I am having a hard time solving for v_+. any help is greatly appreciatd, maybe if you guys can not solve the problem for...
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