Unit 3.3 - The Operational Amplifier

Unit 3.3 - The Operational Amplifier - The Operational...

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1 1 Unit 3: Other Circuit Analysis Techniques Unit 3.3 – The Operational Amplifier 2 The Operational Amplifier f In this lecture, you will learn: ± The characteristics of an ideal operational amplifier ± 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 3 The Operational Amplfier f The term is rooted in the days of the analog computer ± A unit used to perform addition, subtraction, multiplication, division, differentiation or integration f Today, the term “op amp” usually refers to a highly integrated circuit capable of performing these same operations by adding external components 4 The 741 Op Amp f One of the first solid-state integrated op-amps (1966) f Still widely used today Inverting input Non-inverting input Output V + V - 2 3 7 4 6 15 Of set nul - + - + Inverting input 2 Non-inverting input 3 V - 4 Offset null 1 7 V + 6 Output 5 Offset Null 8 NC 5 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 Of set nul - + 6 Real World (Non-ideal) Op Amp f All real op amps have: ± A finite input resistance R i ± A finite (but very large) gain called the open-loop gain (A) ± A non-zero output resistance R o ± Current drive limitations ± Power dissipation limitations ± Input offsets that must be dealt with in some circuits v o R i Av d R o - + - v d +
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2 7 The Ideal Operational Amplifier f We will make some assumptions about the op amp characteristics that simplify circuit analysis f For many circuits, these simplifications are justified f The ideal operational amplifier can be characterized as follows: ± Infinite open loop gain, A ± Infinite input resistance, R i ± Zero output resistance, R o 0 v o R i Av d R o - + - v d + 8 Real vs. Ideal Specs. f The ideal op amp: ± Infinite open loop gain, A ± Infinite input resistance, R i ± Zero output resistance, R o 0 f Real op-amp specs (LM741): ± A = 200,000 (typical) ± R i = 6 M (typical) ± R o 300
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Unit 3.3 - The Operational Amplifier - The Operational...

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