EE302Lecture22 - 1 The Operational Amplifier t In this...

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Unformatted text preview: 1 The Operational Amplifier t In this lecture, you will learn: s The characteristics of an ideal operational amplifier s The application of the operational amplifier to five circuit configurations: The comparator The inverting amplifier The non-inverting amplifier The summing amplifier The difference amplifier 2 The Operational Amplfier t The term is rooted in the days of the analog computer s A unit used to perform addition, subtraction, multiplication, division, differentiation or integration t Today, the term op amp usually refers to a highly integrated circuit capable of performing these same operations by adding external components 3 The 741 Op Amp t One of the first solid-state integrated op-amps (1966) t Still widely used today Inverting input Non-inverting input Output V + V- 2 3 7 4 6 15 Offset null- +- + Inverting input 2 Non-inverting input 3 V- 4 Offset null 1 7 V + 6 Output 5 Offset Null 8 NC 4 The 741 Op-Amp You get all of this for around 20 cents. Inverting input Non-inverting input Output V + V- 2 3 7 4 6 15 Offset null- + 5 Output Input Characteristics Output-Input Characteristics-20-15-10-5 5 10 15 20-0.20-0.15-0.10-0.05 0.00 0.05 0.10 0.15 0.20 Input Voltage vd in mV O u t p u t V o l t a g e v o in V PositiveSaturationRegionP ositiveSaturationRegion PositiveSaturationRegion PositiveSaturationRegion NegativeSaturationRegionN egativeSaturationRegion NegativeSaturationRegion NegativeSaturationRegion LinearRegionL inearRegion LinearRegion LinearRegion +- + v 1- + v 2-- v d + + v o- 6 The Ideal Operational Amplifier t We will make some assumptions about the o p amp characteristics that simplify circuit analysis. t For many circuits, these simplifications are justified. t The ideal operational amplifier can be characterized as follows: s Infinite open loop gain, A s Infinite input resistance, R i s Zero output resistance, R o v o R i Av d R o- +- v d + 7 Real World (Non-ideal) Op Amp t All real op amps have: s A finite input resistance R i s A finite (but very large) gain called the open-loop gain (A) s A non-zero output resistance R o s Current drive limitations s Power dissipation limitations s Input offsets that must be dealt with in some circuits v o R i Av d R o- +- v d + 8 Real vs. Ideal Specs. t The ideal op amp: s Infinite open loop gain, A s Infinite input resistance, R i s Zero output resistance, R o 0 t Real op-amp specs (LM741): s A = 200,000 (typical) s R i = 6 M (typical) s R o 300 (typical for R L 2k ) v o R i Av d R o- +- v d + o v i Av d- +- v d + 9...
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This note was uploaded on 02/13/2010 for the course EE 302 taught by Professor Mccann during the Spring '06 term at University of Texas at Austin.

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EE302Lecture22 - 1 The Operational Amplifier t In this...

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