Operational Amplifier

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Operational Amplifier
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Ideal OP Amp
Circuit model
Two golden rules to perform calculations on op
amps with negative feedback

• iin0, no current flow into op amp.
• VV-
• Typically one end of op amp is connected to
  ground, therefore, VV- 0V, virtual ground.
  Often V is connected to ground to avoid
  stability problem.

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Applications building block for analog systems

• Amplifiers
• Adders and Substractors
• Integrators Differentiators
• Clock generators
• Filters
• Digital-to-analog converters

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Using op-amps
No flexibility
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Lets build a circuitnoninverting amplifier
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When A is very large
Suppose A106, R19R, R2R

• Gain
• determined by resistance ratio
• insensitive to A, temperature, fab variation

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Why did this happen? Negative feedback
e.g. vIN5V Suppose I perturb the circuit (e.g.
force v0 momentarily to 12V somehow Stable point
is when v?v- Key negative feedback ? portion
of output fed to ve input. e.g. Car antilock
brakes ? small corrections
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How to control a high-strung device

• Antilock brakes

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More op amp insights

• Observe, under negative feedback,
• We also know
• i ? 0
• i- ? 0
• ? Yield an easier analysis method (under negative
  feedback)

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Insightful analysis method under negative
feedback
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Voltage follower
Why is this circuit useful?
has minimum effects on previous and next circuit.
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Inverting Amplifier
Feedback resistor, always to negative input
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Summing Amplifier Add Circuit
If RS1RS2RSNRS
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Non-innverting Amplifier
Feedback resistor, always to negative input
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Differential Amplifier Substractor
Very useful if both signals are corrupted with
noise Electrocardiogram (EKG)