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Chapter 7 Operational-Amplifier and its Applications

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1 Chapter 7 Operational-Amplifier and its Applications
SJTU Zhou Lingling

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 SJTU Zhou Lingling

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. SJTU Zhou Lingling

4 The 741 Op-Amp Circuit General description The input stage
The intermediate stage The output stage The biasing circuits Device parameters SJTU Zhou Lingling

5 SJTU Zhou Lingling

6 General Description 24 transistors, few resistors and only one capacitor Two power supplies Short-circuit protection SJTU Zhou Lingling

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. SJTU Zhou Lingling

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. SJTU Zhou Lingling

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. SJTU Zhou Lingling

10 The Output Stage (a) The emitter follower is a class A output stage. (b) Class B output stage. SJTU Zhou Lingling

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. SJTU Zhou Lingling

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. SJTU Zhou Lingling

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. SJTU Zhou Lingling

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. SJTU Zhou Lingling

15 The Ideal Op Amplifier symbol for the op amp SJTU Zhou Lingling

16 The Ideal Op Amplifier The op amp shown connected to dc power supplies. SJTU Zhou Lingling

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. SJTU Zhou Lingling

18 Equivalent Circuit of the Ideal Op Amp
SJTU Zhou Lingling

19 The Inverting Configuration
The inverting closed-loop configuration. Virtual ground. SJTU Zhou Lingling

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. SJTU Zhou Lingling

23 The Noninverting Configuration
Series-shunt negative feedback. SJTU Zhou Lingling

24 The Noninverting Configuration
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25 The Voltage follower The unity-gain buffer or follower amplifier.
Its equivalent circuit model. SJTU Zhou Lingling

26 The Weighted Summer SJTU Zhou Lingling

27 The Weighted Summer SJTU Zhou Lingling

28 A Single Op-Amp Difference Amplifier
Linear amplifier. Theorem of linear Superposition. SJTU Zhou Lingling

29 A Single Op-Amp Difference Amplifier
Application of superposition Inverting configuration SJTU Zhou Lingling

30 A Single Op-Amp Difference Amplifier
Application of superposition. Noninverting configuration. SJTU Zhou Lingling

31 Integrators The inverting configuration with general impedances in the feedback and the feed-in paths. SJTU Zhou Lingling

32 The Inverting Integrators
The Miller or inverting integrator. SJTU Zhou Lingling

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. SJTU Zhou Lingling

36 The Antoniou Inductance-Simulation Circuit
SJTU Zhou Lingling

37 The Antoniou Inductance-Simulation Circuit
SJTU Zhou Lingling

38 The Op amp-RC Resonator
An LCR second order resonator. SJTU Zhou Lingling

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. SJTU Zhou Lingling

40 The Op amp-RC Resonator
Implementation of the buffer amplifier K. SJTU Zhou Lingling

41 The Op amp-RC Resonator
Pole frequency Pole Q factor SJTU Zhou Lingling

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. SJTU Zhou Lingling

43 Bistable Circuit The bistable circuit (positive feedback loop)
The negative input terminal of the op amp connected to an input signal vI. SJTU Zhou Lingling

44 Bistable Circuit The transfer characteristic of the circuit in (a) for increasing vI. Positive saturation L+ and negative saturation L- SJTU Zhou Lingling

45 Bistable Circuit The transfer characteristic for decreasing vI.
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46 Bistable Circuit The complete transfer characteristics.
SJTU Zhou Lingling

47 A Bistable Circuit with Noninverting Transfer Characteristics
SJTU Zhou Lingling

48 A Bistable Circuit with Noninverting Transfer Characteristics
The transfer characteristic is noninverting. SJTU Zhou Lingling

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. SJTU Zhou Lingling

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. SJTU Zhou Lingling

51 Application of Bistable Circuit as a Comparator
Illustrating the use of hysteresis in the comparator characteristics as a means of rejecting interference. SJTU Zhou Lingling

52 Making the Output Level More Precise
For this circuit L+ = VZ1 + VD and L– = –(VZ2 + VD), where VD is the forward diode drop. SJTU Zhou Lingling

53 Making the Output Level More Precise
For this circuit L+ = VZ + VD1 + VD2 and L– = –(VZ + VD3 + VD4). SJTU Zhou Lingling

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. SJTU Zhou Lingling

55 Generation of Square Waveforms
The circuit obtained when the bistable multivibrator is implemented with the positive feedback loop circuit. SJTU Zhou Lingling

56 Waveforms at various nodes of the circuit in (b).
This circuit is called an astable multivibrator. Time period T = T1+T2 SJTU Zhou Lingling

57 Generation of Triangle Waveforms
SJTU Zhou Lingling

58 Generation of Triangle Waveforms
SJTU Zhou Lingling

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