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Review of op amp circuits

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The following presentation is a part of the level 5 module -- Electronic Engineering. This resources is a part of the 2009/2010 Engineering (foundation degree, BEng and HN) courses from University of …

The following presentation is a part of the level 5 module -- Electronic Engineering. This resources is a part of the 2009/2010 Engineering (foundation degree, BEng and HN) courses from University of Wales Newport (course codes H101, H691, H620, HH37 and 001H). This resource is a part of the core modules for the full time 1st year undergraduate programme.
The BEng & Foundation Degrees and HNC/D in Engineering are designed to meet the needs of employers by placing the emphasis on the theoretical, practical and vocational aspects of engineering within the workplace and beyond. Engineering is becoming more high profile, and therefore more in demand as a skill set, in today’s high-tech world. This course has been designed to provide you with knowledge, skills and practical experience encountered in everyday engineering environments.

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  • 1. Review of Op-Amp Circuits Electronic Engineering © University of Wales Newport 2009 This work is licensed under a Creative Commons Attribution 2.0 License .
  • 2.
    • The following presentation is a part of the level 5 module -- Electronic Engineering. This resources is a part of the 2009/2010 Engineering (foundation degree, BEng and HN) courses from University of Wales Newport (course codes H101, H691, H620, HH37 and 001H). This resource is a part of the core modules for the full time 1 st year undergraduate programme.
    • The BEng & Foundation Degrees and HNC/D in Engineering are designed to meet the needs of employers by placing the emphasis on the theoretical, practical and vocational aspects of engineering within the workplace and beyond. Engineering is becoming more high profile, and therefore more in demand as a skill set, in today’s high-tech world. This course has been designed to provide you with knowledge, skills and practical experience encountered in everyday engineering environments.
    • Contents
    • Review of Linear Op-Amp Circuits
    • Inverting Amplifier
    • Non-inverting Amplifier
    • Unity Buffer
    • Summing Amplifier
    • Non-Inverting Summing Amplifier
    • Difference Amplifier
    • Integrator
    • Differentiator
    • Uses of Linear Op-Amp Circuits
    • Ideal Op-Amp Linear Circuit Analysis
    • Credits
    • In addition to the resource below, there are supporting documents which should be used in combination with this resource. Please see:
    • Clayton G, 2000, Operational Amplifiers 4th Ed, Newnes 
    • James M, 2004, Higher Electronics, Newnes
    Oscillators
  • 3. Review of Linear Op-Amp Circuits
    • We will quickly review the analysis & design of linear op-amp circuits that use negative feedback :
      • Inverting amplifier
      • Non-inverting amplifier
      • Unity Buffer
      • Summing amplifiers
      • Difference amplifier
      • Integrator
      • Differentiator
    Review of Op-Amp Circuits
  • 4. INVERTING AMPLIFIER We can generate the following equations: Combining these gives us: This is true for any amplifier. + - Rin Vin Rf Vout Va Iin If Ia
  • 5.
    • But this is an op-amp and therefore we can make certain assumptions…
      • Va = 0. This is because the gain is very large and therefore Va will be very small.
      • Ia = 0. This is because the input impedance is very large and therefore Ia will be very small.
    • We can therefore rewrite the equation:
    or The minus sign indicates that this is an inverting amplifier. This set up is called a Virtual Earth Amplifier as the amplifier input terminal (-) is at earth potential as the + input is at earth.
  • 6. NON-INVERTING AMPLIFIER The current I flows through both resistors as no current flows into the op-amp (assumption 2) from which But Vf = Vin as the difference in input voltages is zero (assumption 1), so + - R1 Vin R2 Vout Vf I
  • 7. or Design an amplifier that has a variable gain from 15 to 30. (use a 100K  variable resistor)
  • 8. UNITY BUFFER In the circuit Vout = Vin – what is the purpose of this circuit? + - Vin Vout
  • 9. SUMMING AMPLIFIER (Inverting) This is a virtual earth amplifier. and Using Kirchhoff we can say: + - V2 Rf Vout Va I2 If V1 I1 V3 I3 R1 R2 R3
  • 10. If R1 = R2 = R3 = Rin If Rin = Rf
    • Notes:
    • If an input is negative it will be subtracted
    • Weighting can be applied to inputs by altering the value of the input resistance – if R1 was half the value of the other input resistors we would have:
  • 11. SUMMING AMPLIFIER (Non-inverting) The output of the amplifier will be: What does V’ equal? – Use superposition theory + - V2 R1 Vout V’ V1 V3 R R R R2
  • 12. The same is true for the other inputs so we can say: if the gain is set to 3 then: What would we get if – V1 resistor = R V2 resistor = 2R V3 resistor = 3R? V1 R R R V’
  • 13. SUBTRACTOR (DIFFERENCE) AMPLIFIER To determine the output we will use Superposition. V1 input only V2 = 0 We have a non inverting amplifier with a gain of: + - R1 V2 R2 Vout R1 V1 R2 I
  • 14. The voltage appearing on the + input V+ is equal to: The output is therefore input times gain: V2 input only V1 = 0 The V+ input will be at 0v and the amplifier will act as an inverting amplifier. The output will therefore be:
  • 15. Combining these gives us the overall output equation: This circuit will take the difference between two inputs and amplify it by a factor R2/R1.
  • 16. INTEGRATING AMPLIFIER We can generate the following equations: From what we know of op-amps we can say:   V- is at earth potential (virtual earth point) The current through the resistor equals the current through the capacitor. C R Vout Vin I
  • 17. The current through a capacitor depends upon the rate of change of voltage across it and the capacitor value.   Equating gives     Hence the name integrator.
  • 18. DIFFERENTIATING AMPLIFIER We can generate the following equations: C R Vout Vin I Once again from what we know of op-amps we can say:   V- is at earth potential (virtual earth point) The current through the resistor equals the current through the capacitor.
  • 19. The current through a capacitor depends upon the rate of change of voltage across it and the capacitor value.   Equating gives     Hence the name differentiator.
  • 20. Uses of Linear Op-Amp Circuits
    • Amplifiers
      • Signal conditioning
    • Summing Amp
      • Mixing (e.g. audio applications)
      • Analogue arithmetic
    • Integrator
      • Analogue computing
      • Active filter design
    • Difference Amp
      • Noise reduction in audio amplification.
    Review of Op-Amp Circuits
  • 21. Ideal Op-Amp Linear Circuit Analysis
    • When negative feedback is applied, the use of these assumptions makes design/analysis much easier (although not necessarily simple!).
    • Of course, they aren’t really true…
    Review of Op-Amp Circuits
  • 22. Review of Op-Amp Circuits This resource was created by the University of Wales Newport and released as an open educational resource through the Open Engineering Resources project of the HE Academy Engineering Subject Centre. The Open Engineering Resources project was funded by HEFCE and part of the JISC/HE Academy UKOER programme. © 2009 University of Wales Newport This work is licensed under a Creative Commons Attribution 2.0 License . The JISC logo is licensed under the terms of the Creative Commons Attribution-Non-Commercial-No Derivative Works 2.0 UK: England & Wales Licence.  All reproductions must comply with the terms of that licence. The HEA logo is owned by the Higher Education Academy Limited may be freely distributed and copied for educational purposes only, provided that appropriate acknowledgement is given to the Higher Education Academy as the copyright holder and original publisher. The name and logo of University of Wales Newport is a trade mark and all rights in it are reserved. The name and logo should not be reproduced without the express authorisation of the University.