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Lecture 11

Lecture 11. Operational Amplifiers. Topics. Ideal op Amplifiers Ideal OPA circuits analysis Non-ideal op amplifiers Non-ideal OPA circuit analysis. Ideal operational amplifier. Ideal OPA characters. Infinite input impedance Zero output impedance Infinite bandwidth

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Lecture 11

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  1. Lecture 11 Operational Amplifiers Microelectric Circuit by Meiling CHEN

  2. Topics • Ideal op Amplifiers • Ideal OPA circuits analysis • Non-ideal op amplifiers • Non-ideal OPA circuit analysis Microelectric Circuit by Meiling CHEN

  3. Ideal operational amplifier Ideal OPA characters • Infinite input impedance • Zero output impedance • Infinite bandwidth • Infinite open-loop gain • Zero common-mode gain (infinite CMRR) Microelectric Circuit by Meiling CHEN

  4. Microelectric Circuit by Meiling CHEN

  5. Microelectric Circuit by Meiling CHEN

  6. Negative feedback Positive feedback Microelectric Circuit by Meiling CHEN

  7. Non-ideal cases Ideal OPA characters Microelectric Circuit by Meiling CHEN

  8. Consider finite open-loop gain Microelectric Circuit by Meiling CHEN

  9. Input and output resistance Example 2.1 An impractically large value So we may have the problem of input resistance. Microelectric Circuit by Meiling CHEN

  10. Output resistance Microelectric Circuit by Meiling CHEN

  11. Example 2.2 Example 2.2: Comparing with Example 2.1 Design a amplifier with a gain –100 and an input resistance of 1M. Example 2.1: Microelectric Circuit by Meiling CHEN

  12. Exercise 2.6 Microelectric Circuit by Meiling CHEN

  13. Weighted summer Microelectric Circuit by Meiling CHEN

  14. Exercise D2.8 Microelectric Circuit by Meiling CHEN

  15. Non-inverting amplifier Ideal case: Non-ideal case: Microelectric Circuit by Meiling CHEN

  16. Voltage follower Microelectric Circuit by Meiling CHEN

  17. Exercise D2.9 Exercise D2.13 Microelectric Circuit by Meiling CHEN

  18. Why use difference amplifier ? CMRR ( Common-Mode Rejection ratio ) Different-mode input Common-mode input Microelectric Circuit by Meiling CHEN

  19. Difference Amplifier Method I: Microelectric Circuit by Meiling CHEN

  20. Different-mode input Method I: superposition Microelectric Circuit by Meiling CHEN

  21. CMRR=infinite Common-mode input CMRR=infinite Microelectric Circuit by Meiling CHEN

  22. Consider the problem of input resistance Differential mode input resistance Microelectric Circuit by Meiling CHEN

  23. Instrumentation Amplifier Not is differential mode, common mode input can be pass. • Defects: • Common mode gain=differential mode gain. • Resistance have to match. Advantages: Big differential gain Microelectric Circuit by Meiling CHEN

  24. Remove the point x Microelectric Circuit by Meiling CHEN

  25. DC non-ideal characters • Finite open loop gain ( finite CMRR) • Finite BW • Offset voltage • Input bias and offset current Microelectric Circuit by Meiling CHEN

  26. Frequency response (open-loop) Microelectric Circuit by Meiling CHEN

  27. Frequency response (closed loop) Microelectric Circuit by Meiling CHEN

  28. Output voltage saturation Microelectric Circuit by Meiling CHEN

  29. Slew rate Microelectric Circuit by Meiling CHEN

  30. Offset voltage From the component mismatches in the input differential stage Output = + saturation or - saturation May be positive or negative Microelectric Circuit by Meiling CHEN

  31. Reduce the allowable signal swing • When input is dc we would not know the output is due to vos or signals Microelectric Circuit by Meiling CHEN

  32. Solution 1: Offset-nulling terminals Solution 2: Capacitive coupling (only ac signal be amplified) Microelectric Circuit by Meiling CHEN

  33. Offset current Input bias currents Input offset current Upper limit R2 Microelectric Circuit by Meiling CHEN

  34. Solution : introducing R3 Microelectric Circuit by Meiling CHEN

  35. Inverse amplifier Reduce the effect of Vos Reduce the effect of Ios Non-inverse amplifier Reduce the effect of Vos Reduce the effect of Ios Microelectric Circuit by Meiling CHEN

  36. Integrator & Differentiator Microelectric Circuit by Meiling CHEN

  37. Microelectric Circuit by Meiling CHEN

  38. Miller Integrator Microelectric Circuit by Meiling CHEN

  39. Consider Vos offset voltage Consider Ios offset current Microelectric Circuit by Meiling CHEN

  40. Solution : Microelectric Circuit by Meiling CHEN

  41. Microelectric Circuit by Meiling CHEN

  42. Example 2.7 sketch output response Case I: Case II: Microelectric Circuit by Meiling CHEN

  43. Differentiator Microelectric Circuit by Meiling CHEN

  44. Problem *2.31 Microelectric Circuit by Meiling CHEN

  45. Problem *2.43 Microelectric Circuit by Meiling CHEN

  46. Problem **2.69 Microelectric Circuit by Meiling CHEN

  47. Problem *2.77 Microelectric Circuit by Meiling CHEN

  48. Problem *2.78 Microelectric Circuit by Meiling CHEN

  49. Problem C*2.126 Microelectric Circuit by Meiling CHEN

  50. Non-ideal OP amplifiers • Type A: Finite open-loop gain (unknown) • Type B: Finite open-loop gain = K • Type C: • Infinite input impedance • Zero output impedance • Zero common-mode gain • Infinite open-loop gain • Infinite bandwidth Ideal OPA characters Microelectric Circuit by Meiling CHEN

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