INTRODUCTION...................................................................................................................................7
Computation Control Instrumentation .............................................................................................7
The Feedback Technique ...............................................................................................................7
Notation and Terminology...............................................................................................................8
Input Terminals..............................................................................................................................9
Output Terminals ............................................................................................................................9
Power Connections ......................................................................................................................10
Summary of Notation....................................................................................................................10
Electrical Circuit Models ...............................................................................................................10
Circuit Notation............................................................................................................................11
The Ideal Operational Amplifier ....................................................................................................12
Defining the Ideal Operational Amplifier........................................................................................12
A Summing Point Restraint...........................................................................................................13
CIRCUITS AND ANALYSES USING THE IDEAL OPERATIONAL AMPLIFIER.................................14
The Desirability of Feedback ........................................................................................................14
Two Important Feedback Circuits .................................................................................................15
Voltage Follower..........................................................................................................................15
Non-Inverting Amplifier .................................................................................................................17
INVERTING AMPLIFIER ..............................................................................................................18
Intuitive Analysis Techniques........................................................................................................19
Current Output.............................................................................................................................20
Reactive Elements.......................................................................................................................20
Integrator .....................................................................................................................................21
Differentiator................................................................................................................................21
Voltage Adder..............................................................................................................................23
Scaling Summer ...........................................................................................................................23
Combining Circuit Functions .........................................................................................................24
Differential Input Amplifier.............................................................................................................24
Balanced Amplifier.......................................................................................................................25
Ideal-Real Comparison.................................................................................................................27
CHARACTERISTICS OF PRACTICAL OPERATIONAL AMPLIFIERS...............................................29
Open Loop Characteristics ...........................................................................................................29
Open Loop Operation ...................................................................................................................30
Output Limiting .............................................................................................................................30
FREQUENCY DEPENDENT PROPERTIES ........................................................................................31
Introduction..................................................................................................................................31
Open Loop Gain and the Bode Plot ..............................................................................................31
Bode Plot Construction.................................................................................................................31
Closed Loop Gain.........................................................................................................................32
Stability........................................................................................................................................33
Compensation ..............................................................................................................................33
Compensation Changes ...............................................................................................................34
Bandwidth....................................................................................................................................35
Loop Gain....................................................................................................................................35
The Significance of Loop Gain......................................................................................................36
BODE PLOTS AND BASIC PRACTICAL CIRCUITRY........................................................................37
Voltage Follower..........................................................................................................................37
SBOA092A
4 HANDBOOK OF OPERATIONAL AMPLIFIER APPLICATIONS
Inverter ........................................................................................................................................ 37
X1000 Amplifier ............................................................................................................................ 38
Differentiator................................................................................................................................ 38
INTEGRATOR............................................................................................................................. 40
OTHER IMPORTANT PROPERTIES OF OPERATIONAL AMPLIFIERS............................................ 41
Summing Point Restraints ............................................................................................................ 41
Closed Loop Impedance Levels.................................................................................................... 42
Output Impedance....................................................................................................................... 42
Input Impedance.......................................................................................................................... 43
Differential Inputs and Common Mode Rejection.......................................................................... 44
The Common Mode Voltage Limit ................................................................................................ 44
Offset........................................................................................................................................... 44
Drift 45
Capacitive Loading....................................................................................................................... 45
VOLTAGE DETECTORS AND COMPARATORS ............................................................................... 46
Voltage Limiting Operational Amplifiers ........................................................................................ 46
THE VOLTAGE FOLLOWER .............................................................................................................. 49
BUFFERS AND ISOLATION AMPLIFIERS .................................................................................. 50
Inverting Buffer Adjustable Gain ................................................................................................... 50
Balanced Output.......................................................................................................................... 50
VOLTAGE AND CURRENT REFERENCES........................................................................................ 50
Isolated Standard Cell .................................................................................................................. 51
Constant Current Generator ......................................................................................................... 51
Buffer Variation............................................................................................................................ 52
Presettable Voltage Source .......................................................................................................... 52
Reference Voltage Supply ............................................................................................................ 52
THE NON-INVERTING AMPLIFIER ....................................................................................................53
THE INVERTING AMPLIFIER ............................................................................................................. 54
INTEGRATORS.................................................................................................................................. 55
PRACTICAL INTEGRATORS.............................................................................................................. 55
Simple Integrators ........................................................................................................................ 56
Summing Integrator ...................................................................................................................... 58
Double Integrator......................................................................................................................... 58
Differential Integrator .................................................................................................................... 59
AC Integrator ............................................................................................................................... 59
Augmenting Integrator .................................................................................................................. 59
DIFFERENTIATORS........................................................................................................................... 61
With “Stop” .................................................................................................................................. 61
Low Noise ................................................................................................................................... 62
Augmented Differentiator.............................................................................................................. 62
THE VOLTAGE SUMMER................................................................................................................... 63
SUMMING AND AVERAGING AMPLIFIERS................................................................................ 64
Adder........................................................................................................................................... 64
Scaling Adder.............................................................................................................................. 64
Direct Addition............................................................................................................................. 65
Averager...................................................................................................................................... 65
Weighted Average........................................................................................................................ 66
THE DIFFERENTIAL INPUT AMPLIFIER............................................................................................ 67
Adder-Subtractor or Floating Input Combiner ............................................................................... 68
SBOA092A
HANDBOOK OF OPERATIONAL AMPLIFIER APPLICATIONS 5
THE DIFFERENTIAL (BALANCED) OUTPUT AMPLIFIER.................................................................69
DC AMPLIFIERS ................................................................................................................................70
Simple Inverting sign changing amplifier.......................................................................................70
Chopper Stabilized .......................................................................................................................70
Simple Gain Control......................................................................................................................70
Linear Gain Control ......................................................................................................................71
Simple Non-Inverting ....................................................................................................................71
Power Booster.............................................................................................................................71
Differential Output.........................................................................................................................73
Gain Control ................................................................................................................................73
Inverting Gain Control...................................................................................................................73
DIFFERENTIAL AMPLIFIERS......................................................................................................74
Subtractor....................................................................................................................................74
Difference Amplifier ......................................................................................................................74
Common Mode Rejection .............................................................................................................75
Differential Input-Output................................................................................................................75
AC AMPLIFIERS ................................................................................................................................76
DC Amplifiers with Blocking Capacitors ........................................................................................76
Simple Amplifier .....................................................................................................................................76
Single Supply .........................................................................................................................................76
Non-Inverting ..........................................................................................................................................77
Double Rolloff.........................................................................................................................................77
AC Preamplifier ......................................................................................................................................78
CURRENT OUTPUT DEVICES............................................................................................................79
Feedback Loop............................................................................................................................79
Simple Meter Amplifier..................................................................................................................79
Meter Amplifier .............................................................................................................................80
Current Injector............................................................................................................................80
Linear Current Source ..................................................................................................................81
Deflection Coil Driver ....................................................................................................................82
OSCILLATORS AND MULTI VIBRATORS .........................................................................................83
Simple Oscillator..........................................................................................................................83
Wien Bridge Oscillator ..................................................................................................................83
PHASE LEAD AND LAG NETWORKS ...............................................................................................84
Lag Element ................................................................................................................................84
Adjustable Lag.............................................................................................................................84
Lag value linear with R setting......................................................................................................85
Adjustable Lead...........................................................................................................................85
Lead-Lag .....................................................................................................................................86
Time Delay ..................................................................................................................................86
ADDITIONAL CIRCUITS .....................................................................................................................87
Absolute Value .............................................................................................................................87
Peak Follower..............................................................................................................................87
Precision Rectifier........................................................................................................................88
AC to DC Converter......................................................................................................................88
Full Wave Rectifier .......................................................................................................................89
Rate Limiter .................................................................................................................................89
Time Delay ..................................................................................................................................90
Selective Amplifier ........................................................................................................................91
SECTION III: SELECTING THE PROPER OPERATIONAL AMPLIFIER ...........................................92
SBOA092A
6 HANDBOOK OF OPERATIONAL AMPLIFIER APPLICATIONS
Focus on Limiting Specifications................................................................................................... 92
Avoid Closed Loop vs. Open Loop Confusion............................................................................... 92
Selection Check List ..................................................................................................................... 92
Assistance Available from Texas Instruments............................................................................... 93
References......................................................................................................................................... 93
Figures
Figure 1. Operational Amplifier with Feedback .............................................................................8
Figure 2. Texas Instruments Standard Symbols ...........................................................................8
Figure 3. Op Amp Package Options ...............................................................................................9
Figure 4. Power Supply Connections........................................................................................... 10
Figure 5. Summary of Notation Introduced.................................................................................. 10
Figure 6. Circuit Model of the Single Ended Operational Amplifier ........................................... 10
Figure 7. Circuit Model of the Differential Output Operational Amplifier................................... 11
Figure 8. Notation and Terms Used in Closed Loop Circuits ..................................................... 11
Figure 9. Equivalent Circuit of the Ideal Operational Amplifier .................................................. 12
Figure 10. Open Loop Operation .................................................................................................... 14
Figure 11. Basic Amplifier Circuits................................................................................................. 15
Figure 12. Voltage Follower ............................................................................................................ 15
Figure 13. Feedback Resistor Added to the Voltage Follower ..................................................... 16
Figure 14. Non-Inverting Amplifier ................................................................................................. 17
Figure 15. Non-Inverting Amplifier Re-Drawn to Show Similarity to the Voltage Follower......... 17
Figure 16. Non-Inverting Amplifier Analyzed as a Voltage Divider .............................................. 17
Figure 17. Inverting Amplifier ......................................................................................................... 18
Figure 18. Intuitive Devices for Analysis of Circuits Based on the Inverting Amplifier.............. 19
Figure 19. Inverting Amplifier as a Linear Current Output Device ............................................... 20
Figure 20. General Form of the Inverting Amplifier....................................................................... 20
Figure 21. Integrator Circuit............................................................................................................ 21
Figure 22. Differentiator Circuit ...................................................................................................... 21
Figure 23. An Intuitive Picture of the Differentiator....................................................................... 22
Figure 24. Voltage Adding Circuit .................................................................................................. 23
Figure 25. Scaling Summer Circuit................................................................................................. 24
Figure 26. Differential Input Amplifier Circuit ................................................................................ 24
Figure 27. Analyzing the Differential Input Amplifier Circuit as Non-Inverting Amplifier ........... 25
Figure 28. The Differential Output Operational Amplifier ............................................................. 26
Figure 29. Equivalent Circuit of a Real Operational Amplifier...................................................... 27
Figure 30. Amplifier Circuit Using a Real Operational Amplifier .................................................. 27
Figure 31. Input-Output Transfer Relation for the Open Loop Operational Amplifier................. 29
Figure 32. Bode Plot of an Operational Amplifier and its Linear Approximation........................ 31
Figure 33. Sketching the Bode Plot Approximation for Figure 32................................................ 32
Figure 34. Closed Loop Gain of a X100 (40 dB) Inverting Amplifier............................................. 32
Figure 35. The Effect of Internal Phase Compensation................................................................. 33
Figure 36. Composite Bode Plots Showing Stability Provided by Proper Phase Compensation34
Figure 37. The Effect of Internal Compensation for Gains Greater Than 1.................................. 34
Figure 38. Instability when an Uncompensated Amplifier is Used at Gains Lower Than the
Designated Level......................................................................................................... 35
Figure 39. Loss of High Frequency Response When Heavy Feedback is Used.......................... 36
Figure 40. Voltage Follower Circuit ................................................................................................ 37
Figure 41. Voltage Inverter Circuit.................................................................................................. 37
SBOA092A
HANDBOOK OF OPERATIONAL AMPLIFIER APPLICATIONS 7
Figure 42. 60 dB Amplifier Circuits.................................................................................................38
Figure 43. Differentiator Circuit ......................................................................................................38
Figure 44. Differentiator With “Stop” .............................................................................................39
Figure 45. Differentiator With “Double Stop”.................................................................................39
Figure 46. Integrator Circuit............................................................................................................40
Figure 47. DC Summing Point Conditions .....................................................................................41
Figure 48. Voltage Follower ............................................................................................................42
Figure 49. Voltage Follower ............................................................................................................43
Figure 50. Inverting Amplifier with Current Offset Control ...........................................................44
Figure 51. Drift Stabilizing the Inverting Amplifier ........................................................................45
Figure 52. Gain Peaking Caused by Capacitive Loading ..............................................................45
Figure 53. Voltage Limiting Operational Amplifiers ......................................................................46
Figure 54. Fully Clamped Voltage Comparator..............................................................................47
Tables
Table 1. Compound Amplifier, Resulting Performance .............................................................72
Table 2. Current Source Scaling Resistors ................................................................................81
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