Student Lecture #1: Operational Amplifiers

Operational AmplifiersJames KellyNathan KnightGustavo LeePresentation OutlineIntroductionCharacteristics of Ideal and Real Op-AmpsBasic Circuits of Op-AmpsApplicationsExerciseWhat is an Op-Amp?An Operational Amplifier (known as an Op-Amp) is an integrated circuit that sets an output voltage based on the input voltages provided.In a circuit, it is used to perform an operation and an amplification where the operation may be add, subtract, filter, integrate, differentiate, etc.Op-Amps are composed of transistors, resistors, capacitors, and diodes.

An amplifier that has more gain than the application required. Some of the amplifier output signal is fed back to the input in a manner that makes the circuit gain (amplifier + feedback components) dependent on the feedback rather than the amplifier gain. The circuit gain is dependent on the passive feedback components rather than the active amplifier. This is called negative feedback, and it is the underlying operating principle for all modern day op amps.

3Brief History1941: Karl Swartzel of Bell Labs developed the first Op-Amp.Used 3 vacuum tubes, only one input (inverting), and operated on + 350 V to achieve 90 dB gain.

1947: Loebe Julie developed the Op-Amp as it is known today, with two inputs inverting and non-inverting.The differential input made a whole range of new functionality possible.

1953: First commercially available Op-Amp.George A. Philbrick Researches(GAP-R). GAP-R pioneered the first reasonable-cost, mass-producedoperational amplifier

1961: Advent of solid-state, discrete Op-Amps.Made possible by the invention of the silicon transistor, which led to the concept of Integrated Circuits (IC)Reduced power input to 15V to 10V

1962: Op-Amp in a potted module.Packaging in small black boxes allowed for integration with a circuit

The heart of the analog computer was a device called an operational amplifier because it could be configured to perform many mathematical operations such as multiplication, addition, subtraction, division, integration, and differentiation on the input signals. The name was shortened to the familiar op amp, as we have come to know and love them. The op amp used an amplifier with a large open loop gain, and when the loop was closed, the amplifier performed the mathematical operations dictated by the external passive components.

4Brief History1963: First monolithic IC Op-Amp, the A702, designed by Bob Widlar at Fairchild Semiconductor.Monolithic ICs consist of a single chip

1968: Release of the A741The A741 became the canonical Op-Amp, from which many modern op-amps base their pinout from, and is still in production today.

ParameterRangeFrequency Spectrum5-kHz to beyond 1-GHz GBWSupply Voltage0.9 V to a maximum 1000 VInput OffsetsApproximately Zero The latest generation op amps cover the frequency spectrum from 5-kHz GBW to beyond 1-GHz GBW. The supply voltage ranges from guaranteed operation at 0.9 V to absolute maximum voltage ratings of 1000 V. The input current and input offset voltage has fallen so low that customers have problems verifying the specifications during incoming inspection. The op amp has truly become the universal analog IC because it performs all analog tasks. 5Presentation OutlineIntroductionCharacteristics of Ideal and Real Op-AmpsBasic Circuits of Op-AmpsApplicationsExerciseBasic Op-Amp (Open-Loop)

Ideal Op-Amp

Several assumptions have to be made before the ideal op amp analysis can proceed. First, assume that the current flow into the input leads of the op amp is zero. Second, the output impedance of the ideal op amp is zero. The ideal op amp can drive any load without an output impedance dropping voltage across it. The output impedance of most op amps is a fraction of an ohm for low current flows, so this assumption is valid in most cases. Third, the op amp gain is assumed to be infinite, hence it drives the output voltage to any value to satisfy the input conditions. This assumes that the op amp output voltage can achieve any value. Fourth, the frequency response of the ideal op amp is flat; this means that the gain does not vary as frequency increases. By constraining the use of the op amp to the low frequencies, we make the frequency response assumption true.

8Real Op-Amp

9SaturationVinVoutVsat+Vsat-SaturationCutoff PointsSlope = G10Presentation OutlineIntroductionCharacteristics of Ideal and Real Op-AmpsBasic Circuits of Op-AmpsApplicationsExerciseOpen Loop vs. Closed LoopA closed-loop op-amp has feedback from the output back to one of the inputs, whereas an open-loop op-amp does not.

Open-LoopClosed-LoopNegative vs. Positive FeedbackNegative feedback connects the output to the inverting input (-), whereas positive feedback connects the output to the non-inverting input (+).

Positive FeedbackNegative Feedback13Negative vs. Positive: OutputNegative feedback op-amps can produce any voltage in the supply power range.Positive feedback op-amps can only produce the maximum and minimum voltages of the range.VinVoutVsat+Vsat-Negative FeedbackVinVoutVsat+Vsat-Positive FeedbackInverting Op-Amp

Non-Inverting Op-Amp

Integrating Op-Amp

Derivative Op-AmpDifferential Op-Amp

Summing Op-Amp

Presentation OutlineIntroductionCharacteristics of Ideal and Real Op-AmpsBasic Circuits of Op-AmpsApplicationsExerciseApplicationsActive filtersSignal processingDigital Image processingStrain gaugesControl circuitsPID controllers for aircraftPI controllers for temperature measurement circuitryAnd much more

22Low-Pass Filter High-Pass Filter

23Bandpass Filter Notch Filter

Strain GaugeStrain gauges consist of a pattern of resistive foil mounted on a backing material.As the foil is subjected to stress, the resistance of the foil changes in a defined way.This results in an output signal directly related to the stress value, typically a few millivolts.Op-Amps are utilized to amplify the output signal level to 5~10 V, a suitable level for application to data collection systems.

PID Controller

PID ControllerAnd much moreComparatorsDetectorsThreshold detectorZero-level detectorOscillatorsWien bridge oscillatorRelaxation oscillatorLevel shifters

Presentation OutlineIntroductionCharacteristics of Ideal and Real Op-AmpsBasic Circuits of Op-AmpsApplicationsExerciseExercise

ReferencesCetinkunt, Sabri. Mechatronics. Hoboken, NJ: John Wiley & Sons Inc., 2007.Jung, Walter G. Op Amp Applications Handbook. Analog Devices, Inc., 2005.Operational Amplifier. http://en.wikipedia.org/wiki/Operational_amplifier.Operational Amplifier Applications. http://en.wikipedia.org/wiki/Operational_amplifier_applications.The Strain Gauge. http://web.deu.edu.tr/mechatronics/TUR/strain_gauge.htm.The PID Controller. http://en.wikipedia.org/wiki/PID_controller.Feedback in Electronic Circuits: An Introduction. http://ecee.colorado.edu/~ecen4827/lectures/dm_feedback1.pdf.Differentiator and Integrator Circuits http://www.allaboutcircuits.com/vol_3/chpt_8/11.html.Inverting Op-Amp http://www.wiringdiagrams21.com/2009/12/17/basic-inverting-op-amp-circuit-diagram/

The EndQuestions?