電路與電子技術(shù)：Chapter 12 Operational Amplifiers

1、Chapter 12 Operational Amplifiers1.List the characteristics of ideal op amps.2. Identify negative feedback in op-amp circuits.3. Analyze ideal op-amp circuits that have negative feedback using the summing-point constraint.4. Understand the operation principal of summing, integrators, differentiators

2、. The first Op-Amps were invented during the time of the Second World War Dr. C. A. Lovell of Bell Lab introduced the Op-Amp George A. Philbrick independently introduced a single vacuum tube operational amplifier in 1948. So, Op-Amps are NOT new!IDEAL OPERATIONAL AMPLIFIERSFigure 12.1 Circuit Symbol

3、 for the op amp.21vvvid21cm21vvvidifferential component common-mode componentSUMMING-POINT CONSTRAINTOperational amplifiers are almost always used with negative feedback, in which part of the output signal is returned to the input in opposition to the source signal.In a negative feedback system, the

4、 ideal op-amp output voltage attains the value needed to force the differential input voltage and input current to zero. We call this fact the summing-point constraint.Ideal op-amp circuits are analyzed by the following steps:1.Verify that negative feedback is present.2. Assume that the differential

5、 input voltage and the input current of the op amp are forced to zero. (This is the summing-point constraint.)3. Apply standard circuit-analysis principles, such as Kirchhoffs laws and Ohms law, to solve for the quantities of interest.INVERTING AMPLIFIERS12inRRvvAovSumming OperationQuestion: Averagi

6、ng signal (do you know how?)NONINVERTING AMPLIFIERSFor noninverting amplifier with negative feedback, summing-point constraint holds. Under the ideal-op-ampassumption, the non-inverting amplifier is an ideal voltage amplifier having infinite inputresistance and zero output resistance.12in211111RRvvA

7、RRvvvvvovoinFind voltage gain and input impedance: +-00+-DIFFERENTIAL AND INSTRUMENTATION AMPLIFIERS(not important)Differential amplifiers arewidely used in engineeringinstrumentation.Instrumentation-Quality Differential AmplifierDifferentiator Circuit dtdvRCtvRivdtdvCivvoCoCCCinin+-+CiINTEGRATORS Integrators produce output voltages that are proportional to the running time integral of the input