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lsli03.4up - 03-1 03-1 Operational Amplifiers These are...

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Unformatted text preview: 03-1 03-1 Operational Amplifiers These are common components in conditioning circuits. There are two inputs, v + and v i , two power supplies, + V s and- V s , and an output, v o . +- v o v +- v V S +- V S v o = min { + V s , max {- V s , ( v +- v- ) A }} , were A is the op-amp gain. Ignoring saturation, v o = A ( v +- v- ). Ideal Op-Amp Properties Infinite input impedance. Infinite gain. ( A = ∞ ) Zero output impedance. 03-1 EE 4770 Lecture Transparency. Formatted 13:25, 23 December 1997 from lsli03. 03-1 03-2 03-2 +- v o v +- v V S +- V S Where to Find Ideal Op-Amps An electronics textbook. However, in certain circuits a real op-amp performs almost the same as an ideal op-amp would. Simplifying Assumptions Current into inputs is zero. When used in a negative feedback configuration, v + = v- . Op-Amp Circuits to be Covered Non-inverting amplifier. Inverting amplifier. Summing amplifier. 03-2 EE 4770 Lecture Transparency. Formatted 13:25, 23 December 1997 from lsli03. 03-2 03-3 03-3 Non-Inverting Amplifier R A B R +- v v i o v o = R A + R B R A v i . 03-3 EE 4770 Lecture Transparency. Formatted 13:25, 23 December 1997 from lsli03. 03-3 03-4 03-4 Versatility of Inverting Amplifier Use of Non-Inverting Amplifier in Conditioning Circuits v o = R A + R B R A v i . Traditional Use, Voltage Amplifier Input is v i , output is v o . H c ( v i ) = R A + R B R A v i R A B R +- v v i o 03-4 EE 4770 Lecture Transparency. Formatted 13:25, 23 December 1997 from lsli03. 03-4 03-5 03-5 Non-Inverting Amplifier Example Problem Design a system with output v o = H ( x ) , where process variable x is water level, x ∈ [0 m , 1 m] , and H ( x ) = 10 x V m . Note: most example problems will not be as complete as the archetyp- ical problem covered earlier. Solution: Use same float-and-cable system as in previous example problem. Use 100 kΩ three-terminal variable resistor with 1 V voltage source across fixed terminals: H t ( x ) = 1 x V m . Problem will be solved two ways: First way, we know what kind of conditioning circuit is needed. Second way, we have to determine algebraicly the type of condi- tioning circuit needed. 03-5 EE 4770 Lecture Transparency. Formatted 13:25, 23 December 1997 from lsli03. 03-5 03-6 03-6 First Way: Use Non-Inverting Amplifier Obviously, all that is needed is an amplifier with a gain of 10. A non-inverting amplifier will do....
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This note was uploaded on 11/28/2011 for the course EE 4770 taught by Professor Staff during the Fall '99 term at LSU.

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lsli03.4up - 03-1 03-1 Operational Amplifiers These are...

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