1. Operational Amplifiers
Lecture 11
Operational Amplifiers
Microelectric Circuit by Meiling CHEN

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

3. Microelectric Circuit by Meiling CHEN
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. Microelectric Circuit by Meiling CHEN
Negative feedback
Positive feedback
Microelectric Circuit by Meiling CHEN

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

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

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

11. Microelectric Circuit by Meiling CHEN
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:
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12. Microelectric Circuit by Meiling CHEN
Exercise 2.6
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13. Microelectric Circuit by Meiling CHEN
Weighted summer
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14. Microelectric Circuit by Meiling CHEN
Exercise D2.8
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15. Microelectric Circuit by Meiling CHEN
Non-inverting amplifier
Ideal case:
Non-ideal case:
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16. Microelectric Circuit by Meiling CHEN
Voltage follower
Microelectric Circuit by Meiling CHEN

17. Microelectric Circuit by Meiling CHEN
Exercise D2.9
Exercise D2.13
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18. Microelectric Circuit by Meiling CHEN
Why use difference amplifier ?
CMRR ( Common-Mode Rejection ratio )
Different-mode input
Common-mode input
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19. Microelectric Circuit by Meiling CHEN
Difference Amplifier
Method I:
Microelectric Circuit by Meiling CHEN

20. Microelectric Circuit by Meiling CHEN
Different-mode input
Method I: superposition
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21. Microelectric Circuit by Meiling CHEN
Common-mode input
CMRR=infinite
CMRR=infinite
Microelectric Circuit by Meiling CHEN

22. Microelectric Circuit by Meiling CHEN
Consider the problem of input resistance
Differential mode input resistance
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23. Microelectric Circuit by Meiling CHEN
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. Microelectric Circuit by Meiling CHEN
Remove the point x
Microelectric Circuit by Meiling CHEN

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

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

28. Microelectric Circuit by Meiling CHEN
Output voltage saturation
Microelectric Circuit by Meiling CHEN

29. Microelectric Circuit by Meiling CHEN
Slew rate
Microelectric Circuit by Meiling CHEN

30. Microelectric Circuit by Meiling CHEN
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. Microelectric Circuit by Meiling CHEN
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. Microelectric Circuit by Meiling CHEN
Solution 1: Offset-nulling terminals
Solution 2: Capacitive coupling (only ac signal be amplified)
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33. Microelectric Circuit by Meiling CHEN
Offset current
Input bias currents
Input offset current
Upper limit R2
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34. Microelectric Circuit by Meiling CHEN
Solution : introducing R3
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35. Microelectric Circuit by Meiling CHEN
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
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36. Microelectric Circuit by Meiling CHEN
Integrator & Differentiator
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37. Microelectric Circuit by Meiling CHEN

38. Microelectric Circuit by Meiling CHEN
Miller Integrator
Microelectric Circuit by Meiling CHEN

39. Microelectric Circuit by Meiling CHEN
Consider Vos offset voltage
Consider Ios offset current
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40. Microelectric Circuit by Meiling CHEN
Solution :
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41. Microelectric Circuit by Meiling CHEN

42. Microelectric Circuit by Meiling CHEN
Example 2.7 sketch output response
Case I:
Case II:
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43. Microelectric Circuit by Meiling CHEN
Differentiator
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44. Microelectric Circuit by Meiling CHEN
Problem *2.31
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45. Microelectric Circuit by Meiling CHEN
Problem *2.43
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46. Microelectric Circuit by Meiling CHEN
Problem **2.69
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47. Microelectric Circuit by Meiling CHEN
Problem *2.77
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48. Microelectric Circuit by Meiling CHEN
Problem *2.78
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49. Microelectric Circuit by Meiling CHEN
Problem C*2.126
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50. Microelectric Circuit by Meiling CHEN
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

51. Microelectric Circuit by Meiling CHEN
Type A: Finite open-loop gain (unknown)
Microelectric Circuit by Meiling CHEN

52. Microelectric Circuit by Meiling CHEN
Type B: Finite open-loop gain =K
Microelectric Circuit by Meiling CHEN

53. Microelectric Circuit by Meiling CHEN
Type C:
Microelectric Circuit by Meiling CHEN