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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
2
Overview
• Usage• Op Amp Overview• Fundamental
Operation• Basic Op Amp Circuit• Amplifier Circuits
3
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
5
Overview
• Usage• Op Amp Overview• Fundamental
Operation• Basic Op Amp Circuit• Amplifier Circuits
6
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”
9
Overview
• Usage• Op Amp Overview• Fundamental
Operation• Basic Op Amp Circuit• Amplifier Circuits
10
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
12
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