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Lecture 8: Op Amps and CircuitsNilsson 5.1-5.6

ENG17 (Sec. 1): Circuits I

Summer 1 2014

July 3, 2014

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Overview

• Usage• Op Amp Overview• Fundamental

Operation• Basic Op Amp Circuit• Amplifier Circuits

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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• Amplifier Circuits

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Op Amp Terminals

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Off-note

Bob WidlarCo-creator (w/David Talbert) of first mass-produced op amps

Also created this advertisement

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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• Amplifier Circuits

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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• Amplifier Circuits

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Op Amp Circuit

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Example – Op Amp

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Overview

• Usage• Op Amp Overview• Fundamental

Operation• Basic Op Amp Circuit• Amplifier Circuits

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Inverting Amplifier Circuit

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Operating “Open Loop”

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Noninverting Amplifier Circuit

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Summing Amplifier Circuit

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Difference Amplifier

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Example

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Example