1. Chapter 7 Operational-Amplifier and its Applications
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2. Outline Introduction The 741 Op-Amp Circuit The ideal Op Amp
The inverting configuration
The noninverting configuration
Integrator and differentiator
The antoniou Inductance-simulation Circuit
The Op Amp-RC Resonator
Bistable Circuit
Application of the bistable circuit as a comparator
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3. Introduction
Analog ICs include operational amplifiers, analog multipliers, A/D converters, D/A converters, PLL, etc.
A complete op amp is realized by combining analog circuit building blocks.
The bipolar op-amp has the general purpose variety and is designed to fit a wide range of specifications.
The terminal characteristics is nearly ideal.
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4. The 741 Op-Amp Circuit General description The input stage
The intermediate stage
The output stage
The biasing circuits
Device parameters
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6. General Description
24 transistors, few resistors and only one capacitor
Two power supplies
Short-circuit protection
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7. The Input Stage The input stage consists of transistors Q1 through Q7.
Q1-Q4 is the differential version of CC and CB configuration.
High input resistance.
Current source (Q5-Q7) is the active load of input stage. It not only provides a high-resistance load but also converts the signal from differential to single-ended form with no loss in gain or common-mode rejection.
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8. The Intermediate Stage
The intermediate stage is composed of Q16, Q17 and Q13B.
Common-collector configuration for Q16 gives this stage a high input resistance as well as reduces the load effect on the input stage.
Common-emitter configuration for Q17 provides high voltage gain because of the active load Q13B.
Capacitor Cc introduces the miller compensation to insure that the op amp has a very high unit-gain frequency.
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9. The Output Stage
The output stage is the efficient circuit called class AB output stage.
Voltage source composed of Q18 and Q19 supplies the DC voltage for Q14 and Q20 in order to reduce the cross-over distortion.
Q23 is the CC configuration to reduce the load effect on intermediate stage.
Short-circuit protection circuitry
Forward protection is implemented by R6 and Q15.
Reverse protection is implemented by R7, Q21, current source(Q24, Q22) and intermediate stage.
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10. The Output Stage
(a) The emitter follower is a class A output stage. (b) Class B output stage.
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11. The Output Stage
Wave of a class B output stage fed with an input sinusoid.
Positive and negative cycles are unable to connect perfectly due to the turn-on voltage of the transistors.
This wave form has the nonlinear distortion called crossover distortion.
To reduce the crossover distortion can be implemented by supplying the constant DC voltage at the base terminals.
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12. The Output Stage
QN and QP provides the voltage drop which equals to the summer of turn-on voltages of QN and QP.
This circuit is call Class AB output stage.
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13. The Biasing Circuits
Reference current is generated by Q12, Q11 and R5.
Wilder current provides biasing current in the order of μA.
Double-collector transistor is similar to the two-output current mirror. Q13B provides biasing current for intermediate stage, Q13A for output stage.
Q5, Q6 and Q7 is composed of the current source to be an active load for input stage.
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14. Device Parameters For npn transistors: For pnp transistors:
Nonstandard devices:
Q14 and Q20 each has an area three times that of a standard device.
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15. The Ideal Op Amplifier
symbol for the op amp
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16. The Ideal Op Amplifier
The op amp shown connected to dc power supplies.
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17. Characteristics of the Ideal Op Amplifier
Differential input resistance is infinite.
Differential voltage gain is infinite.
CMRR is infinite.
Bandwidth is infinite.
Output resistance is zero.
Offset voltage and current is zero.
No difference voltage between inverting and noninverting terminals.
No input currents.
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18. Equivalent Circuit of the Ideal Op Amp
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19. The Inverting Configuration
The inverting closed-loop configuration.
Virtual ground.
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20. The Inverting Configuration
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21. The Inverting Configuration
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22. The Inverting Configuration
Shunt-shunt negative feedback
Closed-loop gain depends entirely on passive components and is independent of the op amplifier.
Engineer can make the closed-loop gain as accurate as he wants as long as the passive components are accurate.
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23. The Noninverting Configuration
Series-shunt negative feedback.
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24. The Noninverting Configuration
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25. The Voltage follower The unity-gain buffer or follower amplifier.
Its equivalent circuit model.
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26. The Weighted Summer
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27. The Weighted Summer
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28. A Single Op-Amp Difference Amplifier
Linear amplifier.
Theorem of linear Superposition.
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29. A Single Op-Amp Difference Amplifier
Application of superposition
Inverting configuration
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30. A Single Op-Amp Difference Amplifier
Application of superposition.
Noninverting configuration.
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31. Integrators
The inverting configuration with general impedances in the feedback and the feed-in paths.
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32. The Inverting Integrators
The Miller or inverting integrator.
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33. Frequency Response of the integrator
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34. The op-amp Differentiator
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35. The op-amp Differentiator
Frequency response of a differentiator with a time-constant CR.
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36. The Antoniou Inductance-Simulation Circuit
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37. The Antoniou Inductance-Simulation Circuit
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38. The Op amp-RC Resonator
An LCR second order resonator.
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39. The Op amp-RC Resonator
An op amp–RC resonator obtained by replacing the inductor L in the LCR resonator of a simulated inductance realized by the Antoniou circuit.
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40. The Op amp-RC Resonator
Implementation of the buffer amplifier K.
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41. The Op amp-RC Resonator
Pole frequency
Pole Q factor
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42. Bistable Circuit
The output signal only has two states: positive saturation(L+) and negative saturation(L-).
The circuit can remain in either state indefinitely and move to the other state only when appropriate triggered.
A positive feedback loop capable of bistable operation.
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43. Bistable Circuit The bistable circuit (positive feedback loop)
The negative input terminal of the op amp connected to an input signal vI.
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44. Bistable Circuit
The transfer characteristic of the circuit in (a) for increasing vI.
Positive saturation L+ and negative saturation L-
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45. Bistable Circuit The transfer characteristic for decreasing vI.
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46. Bistable Circuit The complete transfer characteristics.
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47. A Bistable Circuit with Noninverting Transfer Characteristics
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48. A Bistable Circuit with Noninverting Transfer Characteristics
The transfer characteristic is noninverting.
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49. Application of Bistable Circuit as a Comparator
Comparator is an analog-circuit building block used in a variety applications.
To detect the level of an input signal relative to a preset threshold value.
To design A/D converter.
Include single threshold value and two threshold values.
Hysteresis comparator can reject the interference.
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50. Application of Bistable Circuit as a Comparator
Block diagram representation and transfer characteristic for a comparator having a reference, or threshold, voltage VR.
Comparator characteristic with hysteresis.
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51. Application of Bistable Circuit as a Comparator
Illustrating the use of hysteresis in the comparator characteristics as a means of rejecting interference.
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52. Making the Output Level More Precise
For this circuit L+ = VZ1 + VD and L– = –(VZ2 + VD), where VD is the forward diode drop.
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53. Making the Output Level More Precise
For this circuit L+ = VZ + VD1 + VD2 and L– = –(VZ + VD3 + VD4).
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54. Generation of Square Waveforms
Connecting a bistable multivibrator with inverting transfer characteristics in a feedback loop with an RC circuit results in a square-wave generator.
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55. Generation of Square Waveforms
The circuit obtained when the bistable multivibrator is implemented with the positive feedback loop circuit.
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56. Waveforms at various nodes of the circuit in (b).
This circuit is called an astable multivibrator.
Time period T = T1+T2
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57. Generation of Triangle Waveforms
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58. Generation of Triangle Waveforms
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