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Introduction to Operational Amplifiers: Circuits, Symbol, and Applications

Learn about operational amplifiers, their circuit symbol, important terms and equations, ideal and non-ideal characteristics, and various applications. Explore the history and advantages and disadvantages of op-amps.

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Introduction to Operational Amplifiers: Circuits, Symbol, and Applications

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  1. CONTENT Introduction. What isop-amp. Circuitsymbol. 4 .Operational Amplifierspicture. PinDiagram. Important terms andequation. 7.Idealop-amp. Proparty of idealop-amp. Non ideal op-amp. 12.Charrcteristics ofop-amp. 13.Application. 14.Advantages & disadvantages. 15.Conclusion.

  2. INTRODUCTION • The term “operational amplifier” denotes a specialtype of amplifier that, by proper selection of its external components, could be configured for a variety of operations. • HISTORY • First developed by John R. Ragazzine in 1947 with vacuumtube. • In 1960 at FAIRCHILD SEMICONDUCTOR CORPORATION, Robert J. Widlar fabricated op amp with the help of IC fabrication technology. • In1968FAIRCHILDintroducestheop-ampthatwastobecome the industrystandard.

  3. An operational amplifier (op-amp) is aDC-coupledhigh-gainelectronic voltage amplifier • Direct- coupled high gain amplifier usually consisting of one or more differential amplifiers • Output stage is generally a push-pull or push-pull complementary-symmetrypair. • Op amps are differential amplifiers, and their output voltage is proportional to the difference of the two input voltages. The op amp's schematic symbol is shown in the abovefigure • The two input terminals, called the inverting and non-inverting, are labeled with -and • +, • respectively.

  4. Fig.. Ckt symbol for general purposeop-amp Figureshowsthesymbolofop-amp&thepowersupplyconnectionstomakeitwork.The input terminal identified by the ‘-’ and “+” symbols are designated inverting & non- inverting. Their voltage w.r.t ground are denoted as VN & VP and output voltage as VO. Op- amp do not have a zero volt ground terminal Ground reference is established externally by the power supplycommon.

  5. Operational Amplifierspicture Figure : What anOp-Amp looks like in today'sworld Figure: The Philbrick OperationalAmplifier.

  6. Op-amp pindiagram There are 8 pins in a common Op-Amp, like the 741 whichis used in many instructionalcourses. Pin 1: Offsetnull Pin 2:Inverting inputterminal Pin 3: Non-invertinginput terminal Pin 4: –VCC (negative voltage supply) Pin 5: Offsetnull Pin 6: Outputvoltage Pin 7: +VCC (positive voltage supply) Pin 8: NoConnection Figure : Pin connection,LM741.

  7. Important terms andequation a = gain ofamplifiers. Vd= difference between thevoltage. V0= gain ofvoltage. The equation: V0 = a (VP-VN) Electrical parameter: VN V0 Vd Vp Inputbiascurrent(Ib):averageofcurrentthatflowsintotheinvertingand non-inverting input terminal ofop-amp. I/pando/pimpedance:Itistheresistance offeredbytheinputsandtheoutput terminals to varying voltages. The quantity is expressed inOhms. OpenLoopGain:Itis theoverallvoltagegainortheamplification. Inputoffsetvoltage :Itisavoltagethatmust beapplied betweenthetwoterminalofan op-amp to null theo/p. Inputoffsetcurrent(Ii):Thealgebraicdifferentbetweenthecurrentintotheinverting and Non-invertingterminal.

  8. 2 IDEALOP-AMP We know to minimize loading , a well designed voltage amplifier must draw negligible current from the inputsource and must present negligible resistance To the output load . Op-amp areno VO exceptionsowedefinetheidealop-ampip as an ideal voltage amplifier with infinite open loopgain. a infinity Its ideal terminal conditionare rd =infinity ,ro = 0,ip = in =0 iN

  9. IDEAL OP-AMP FOLLOWS THEGIVEN PROPERTY 3 Infinite voltage gaina Infinite input resistance rd so that almost any signal source can drive it and there isno loading of the precedingstage. Zerooutputresistancerosothattheoutputcandriveaninfinitenumberofother device. Zero output voltage when input iszero. Infinite common mode rejection ratio so that the outputcommon mode noise voltage iszero. Infinite slew rate so that output voltage changes occurs simultaneously withinput voltagechanges.

  10. Non -idealop-amp V1=V+ This is opposite to the ideal op-amp only thepositive and Negative terminal are change thereposition. There is a single external input signal V1=V+ that is applied to the +Ve pin ofop-amp. A signal is also made to appear at the -Ve inputterminal, But this is derived from resistors R1 andR2.

  11. CHARACTERISTICS OFIDEAL OP-AMP • Infinite input impedance(about2Mohm) • Low output impedance(about 200ohm) • Very large voltage gain at lowfrequency • Thus,small changes in voltages can be amplified byusing anop-amp • Infinte bandwidth(all frequencies are amplifiedby samefactor • Infinite Common-mode rejectionratio • Infinite Power supply rejectionratio.

  12. Characteristics of non idealop-amp • Finite open-loop gain that causes gainerror • Finite inputimpedance • Non zero outputimpedance • FiniteCMRR • Common-mode inputresistance • Finitebandwidth • Finite power supply rejectionratio.

  13. APPLICATIONS • A to DConverters • Powersource • Zero Crossing Detector(ZCD)

  14. 1.A to DConverters Digital-to-Analog converters (DACs) and Analog-to-Digital converters (ADC)areimportantbuildingblockswith interfacesensors.AnADCtakesananalog signaland convertsa convertsitintoabinaryone,whileaDAC binary signal into an analog value. Figure 1 gives a block diagram of such a system. An example of such a system is a PC soundcard. Figure 1 – Digital processing system with an ADC at the input and a DAC at theoutput

  15. 2. Op-Amp asaCurrent Source A current source can be made from an inverting amplifier as shown in figure. The current in the load resistor, R0 must be equal to the current inR1.Thecurrentis thenobtainedbydividingtheinputvoltagebyR1.

  16. 3.Zero crossing detectorapplications ZCD circuit can be used to check whether the op-amp is in good condition. Zero crossing detectors can be used as frequency counters and for switching purposes in power electronics circuits. ZCD is a basic op ampcircuit.

  17. ADVANTAGESOFANOPAM:- 1.OPAM IS AN UNIVERSAL AMPLIFIER. VOLTAGECOMPARATORS. PRECISIONRECTIFIERS. ANOLOGUE TO DIGITAL CONVERTERS.

  18. DIGITAL TO ANALOGUE CONVERTERS. FILTERS. DIFFRENTIATORS AND INTEGRATORS. VOLTAGE AND CURRENT REGULATOR. ANALOGUE TOCOMPUTERS.

  19. DISADVANTAGES OF ANOPAM:- • 1. MOSTOPAMARE DESIGNED TO FOR LOWER POWEROPERATION. • 2. FOR HIGH OUTPUT IS DESIRED THEN THE OPAM SPECIFICALLY DESIGNED FOR THAT PURPOSE MUST BESEEN. • 3.MOSTCOMMERCIAL OPAM SHUTS OFF WHEN THE LOAD RESISTANCE IS BELOW A SPECIFIC LEVEL.

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