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Unformatted text preview: CHEM*3440 Chemical Instrumentation Topic 5 Operational Amplifiers Circuit Diagram of 741 Op Amp Thanks to Tony van Roon in the Electronics Shop for the use of this picture. Schematic of Op Amp While op amp is complex in detail, there are really only three critical connections to understand its implementation in a circuit. Inverting Input (-) Non-inverting input (+) Output + Important Fundamentals Important basic properties of an Op Amp High input impedance Low output impedance Large gain (10 4 to 10 6 ) Wide unity gain bandwidth Negligible output when inputs are equal Basic operating principles: It draws negligible current into its inputs. It will do whatever it can to make the difference between the inputs 0. It is an active device which drives its output from its power supply. Its response is limited by what its power supply can deliver. An Ideal Op Amp ! ! ! The Inputs The notation on the inputs has nothing to do with the polarity of the signal but instead indicates the phase relationship between an input signal and the output signal. + + V V V V Non-inverting input Inverting input Open Loop Configuration No feedback (see later on). V output = " (V +- V ) Gain " = 10 6 + V V + When the input voltage difference is 15 V, the output is 15 V (the gain is 10 6 ). 15V is the maximum the op amp supply voltage can produce. V output-15 V 15 V Open loop conFguration is only narrowly useful. Frequency Response of Op Amp Note how the extremely high gain is applicable only at very low frequencies. The gain decreases as the frequency increases. Thanks again to Tony van Roon for the figure. Closed Loop Configuration Op amps are employed most often when the output signal is fed back into one of the inputs through some passive electronic device....
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This note was uploaded on 05/15/2010 for the course CHEM 3440 taught by Professor Danthomas during the Fall '06 term at University of Guelph.
- Fall '06