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Lecture 7:Op Amps Intro &Midterm I ReviewNilsson & Riedel 5.1-5.3

ENG17 (Sec. 2): Circuits I

Spring 2014

April 22, 2014

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Overview

• Usage• Op Amp Overview• Fundamental

Operation• Basic Op Amp Circuit• Midterm Review

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Usage: Strain Gauge

• Measure strain by measuring change in resistance

• Problem: hard to measure tiny resistance change

Δ𝑅=2𝑅Δ𝐿𝐿

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How to Measure

• Measure voltage across Wheatstone bridge

• Voltage still a small quantity• …Use an Op Amp to amplify the voltage!

Op Amp = Operational Amplifier

Indicates potential to perform math operations

Indicates potential to amplify input signals

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Overview

• Usage• Op Amp Overview• Fundamental

Operation• Basic Op Amp Circuit• Midterm Review

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Op Amp Terminals

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Terminal Voltage / Current

Follows the Node-Voltage Setup All currents set up as going into the “black box”

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Overview

• Usage• Op Amp Overview• Fundamental

Operation• Basic Op Amp Circuit• Midterm Review

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Voltage Transfer Characteristic

A = gain (multiplying constant)

Use “negative feedback” to stay in linear region

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Overview

• Usage• Op Amp Overview• Fundamental

Operation• Basic Op Amp Circuit• Midterm Review

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Op Amp Circuit

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Overview

• Usage• Op Amp Overview• Fundamental

Operation• Basic Op Amp Circuit• Midterm Review

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Difficulties

PS. Don’t forget about units!

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Thevenin / Norton Equivalents

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Superposition

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Max Power Transfer

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Questions?

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Extra Office Hours

• Tomorrow, Wednesday, 5-7pm• Kemper 3101

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Recap

• Usage• Op Amp Overview• Fundamental

Operation• Basic Op Amp Circuit• Midterm Review