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Unformatted text preview: ecture 28 Lecture 28 Operational Amplifiers Reading: Jaeger 11.111.5 and Notes ECE 3040  Dr. Alan Doolittle Georgia Tech Operational Amplifier Operational Amplifier or OpAmp is a multistage amplifier that is used for eneral electrical signal manipulation general electrical signal manipulation. The numbers of applications possible with Opamps are two numerous to list. Most everyone agrees: OpAmp analysis is significantly easier than transistor analysis. Though they are often internally complex, their use in circuits most often simplifies the overall design. Model The circuit is modeled by an ideal voltage amplifier. Circuit Symbol + + + + V out V in V out V in ECE 3040  Dr. Alan Doolittle Georgia Tech Ideal Operational Amplifier R in = Infinity, Voltage Gain, A v =Infinity at all frequencies R out =0 + + Model V out V in ECE 3040  Dr. Alan Doolittle Georgia Tech Ideal Operational Amplifier Infinite gain means that the device is useless without adding Feedback to control the overall gain to a finite value. i + i out v + Consider the circuit to the right with v in =0 v out i in i v v v A v v out v in i 2 ) v (v for satisfied only is equation above the , A If v ECE 3040  Dr. Alan Doolittle Georgia Tech Feedback forces the two input voltages to be equal! This is known as a virtual ground. R1 and R2 form a Feedback Network Inverting Amplifier Finite voltage gain results from an infinite voltage gain amplifier with negative feedback (feedback that takes a fraction of the output voltage and mixes it back into the negative summation node). i i + i out v + 2 2 2 2 1 resistance input infinite to due ) 2 ) 1 i i i i v R i R i v in o in in v in v out i v 1 in in ground virtual the to due but v R v v i i 2 1 in in 3, and 2 1, Combining R v i ) 3 2 2 1 in 1 1 in v R v R v R R v v R...
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This note was uploaded on 08/23/2011 for the course ECE 3040 taught by Professor Doolittle during the Spring '11 term at University of Florida.
 Spring '11
 Doolittle
 Amplifier, Operational Amplifier

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