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ME 140L - Prelab 5

# ME 140L - Prelab 5 - PRELAB 5 OPERATIONAL AMPLIFIER THEORY...

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PRELAB 5 OPERATIONAL AMPLIFIER: THEORY AND APPLICATIONS 1. OBJECTIVES square4 Understand basic concepts and applications using operational amplifiers. 2. GENERAL NOTATIONS V : Voltage (Volts) R : Resistor (Ohms) C : Capacitor (Farads) 3. OPERATIONAL AMPLIFIER 3.1 OPERATIONAL AMPLIFIER BASICS The term Operational Amplifier was apparently first used by the National Defense Research Council during the World War II, when describing high gain DC amplifier circuits that were able to perform basic mathematical operations. For several years the principal use of Operational Amplifiers was in big analog computers. From now on we will be referring to Operational Amplifiers as Op Amps. The basic characteristics of Op Amps are: square4 Very high input impedance, producing very low input currents. square4 Very high open loop gain square4 Very low output impedance (the amplifier output is not affected by the load) The basic Op Amp is a 5 terminal element: square4 Two Inputs: Inverting (-) and Non Inverting (+) square4 Positive voltage supply square4 Negative voltage supply square4 Output. Extracted from http://www.wikipedia.com

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The most important feature of the Op Amps is its transfer characteristics which are shown in the next figure. V IN on the x axis is defined as the difference between the non inverting input and the inverting input: V IN = V (+) – V (-) The slope of the line in the linear (Yellow) region is called the Op Amp gain (A). The output voltage will be then a function of the gain and the inputs: V OUT = A ( V IN ) Usually the Op Amp gain is very large on the order of 10 5 (100,000). As long as the difference between the non inverting input and the inverting input is small (close to the y axis) we can expect a linear response from the Op Amp. When this difference is too large, the response goes to the non linear region and the Op Amp becomes saturated. The output in the non linear region is limited to the supply voltage values. OPERATIONAL AMPLIFIER TRANSFER CHARACTERISTICS If we connect the inverting input as described in the diagram below and connect the non inverting input to ground (0 Volts reference point), the following relation can be derived: Iglyph817 Iglyph817 F OUT V R R V * = R F
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