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Operational Amplifier

Operational Amplifier. Ideal OP Amp. Circuit model. i in =0, no current flow into op amp. V + =V - Typically one end of op amp is connected to ground, therefore, V + =V - = 0V, virtual ground. Often V + is connected to ground to avoid stability problem.

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Operational Amplifier

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  1. Operational Amplifier

  2. Ideal OP Amp Circuit model • iin=0, no current flow into op amp. • V+=V- • Typically one end of op amp is connected to ground, therefore, V+=V-= 0V, virtual ground. Often V+ is connected to ground to avoid stability problem. Two golden rules to perform calculations on op amps with negative feedback:

  3. Applications: building block for analog systems • Amplifiers • Adders and Substractors • Integrators & Differentiators • Clock generators • Filters • Digital-to-analog converters

  4. Using op-amps No flexibility

  5. Let’s build a circuit……noninverting amplifier

  6. When A is very large Suppose A=106, R1=9R, R2=R • Gain: • determined by resistance ratio • insensitive to A, temperature, fab variation

  7. Why did this happen? Negative feedback e.g. vIN=5V 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

  8. How to control a high-strung device • Antilock brakes

  9. More op amp insights: • Observe, under negative feedback, • We also know • i+  0 • i-  0  Yield an easier analysis method (under negative feedback)

  10. Insightful analysis method: under negative feedback

  11. Voltage follower Why is this circuit useful? has minimum effects on previous and next circuit.

  12. Inverting Amplifier Feedback resistor, always to negative input

  13. Summing Amplifier: Add Circuit If RS1=RS2=…=RSN=RS

  14. Non-innverting Amplifier Feedback resistor, always to negative input

  15. Differential Amplifier: Substractor Very useful if both signals are corrupted with noise: Electrocardiogram (EKG)

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