C H A P T E R 02. Operational Amplifiers

Transcription

1 C H A P T E R 02 Operational Amplifiers

2 The Op-amp Figure 2.1 Circuit symbol for the op amp. Figure 2.2 The op amp shown connected to dc power supplies.

3 The Ideal Op-amp 1. Infinite input impedance 2. Zero output impedance 3. Zero common-mode gain (i.e., infinite common-mode rejection 4. Infinite loop-gain A 5. Infinite bandwidth

4 Differential and Common-mode signals

5 Model of internal of an op-amp by circuit

6 The inverting closed-loop configuration. Figure 2.6 Analysis of the inverting configuration. The circled numbers indicate the order of the analysis steps.

7 Inverting Configuration, taking gain A into account Figure 2.7 Analysis of the inverting configuration taking into account the finite open-loop gain of the op amp.

8 vo R2 R4 = (1 + + v R R I 1 2 R R 4 3 ) Example 2.2. The circled numbers indicate the sequence of the steps in the analysis.

9 Figure 2.9 A current amplifier based on the circuit of Fig The amplifier delivers its output current to R 4. It has a current gain of (1 + R 2 /R 3 ), a zero input resistance, and an infinite output resistance. The load (R 4 ), however, must be floating (i.e., neither of its two terminals can be connected to ground).

10 A weighted summer. A weighted summer capable of implementing summing coefficients of both signs.

11 Figure 2.13 Analysis of the noninverting circuit. The sequence of the steps in the analysis is indicated Sedra/Smith by the circled Copyright numbers by Oxford University Press, Inc.

12 Non-Inverting Configuration 1. Effect of finite loop gain 2. Input/output impedance - Infinite input - Zero output G V V 0 R2 1+ ( ) R1 = R2 1+ ( R1 1+ A i ) R2 1+ ( ) R1 % _ gain _ error = R A + 1+ ( R 2 1 ) x Voltage follower

13 Difference Amplifiers Figure 2.15 Representing the input signals to a differential amplifier in terms of their differential and commonmode components. R R v = O2 = vi 2 ( 1+ ) vi 2 R3 + R4 R1 R1 R

14 Instrumentation Amplifier Figure 2.20 A popular circuit for an instrumentation amplifier. (a) Initial approach to the circuit (b) The circuit in (a) with the connection between node X and ground removed and the two resistors R 1 and R 1 lumped together. This simple wiring change dramatically improves performance. (c) Analysis of the circuit in (b) assuming ideal op amps.

15 Figure 2.22 The inverting configuration with general impedances in the feedback and the feed-in paths. Integrators Differentiator

16 Figure 2.28 Circuit model for an op amp with input offset voltage V OS.

17 Figure E2.21 Transfer characteristic of an op amp with V OS = 5 mv.

18 Figure 2.29 Evaluating the output dc offset voltage due to V OS in a closed-loop amplifier.

19 Figure 2.30 The output dc offset voltage of an op amp can be trimmed to zero by connecting a potentiometer to the two offset-nulling terminals. The wiper of the potentiometer is connected to the negative supply of the op amp.

20 Figure 2.31 (a) A capacitively coupled inverting amplifier. (b) The equivalent circuit for determining its dc output offset voltage V O.

21 Figure 2.32 The op-amp input bias currents represented by two current sources I B1 and I B2.

22 Figure 2.33 Analysis of the closed-loop amplifier, taking into account the input bias currents.

23 Figure 2.34 Reducing the effect of the input bias currents by introducing a resistor R 3.

24 Figure 2.35 In an ac-coupled amplifier the dc resistance seen by the inverting terminal is R 2 ; hence R 3 is chosen equal to R 2.

25 Figure 2.36 Illustrating the need for a continuous dc path for each of the op-amp input terminals. Specifically, note that the amplifier will not work without resistor R 3.

26 Figure 2.37 Determining the effect of the op-amp input offset voltage V OS on the Miller integrator circuit. Note that since the output rises with time, the op amp eventually saturates.

27 Figure 2.38 Effect of the op-amp input bias and offset currents on the performance of the Miller integrator circuit.

28 Figure 2.39 Open-loop gain of a typical general-purpose internally compensated op amp.

29 Figure 2.40 Frequency response of an amplifier with a nominal gain of +10 V/V.

30 Figure 2.41 Frequency response of an amplifier with a nominal gain of 10 V/V.

31 Figure 2.42 (a) A noninverting amplifier with a nominal gain of 10 V/V designed using an op amp that saturates at ±13-V output voltage and has ±20-mA output current limits. (b) When the input sine wave has a peak of 1.5 V, the output is clipped off at ±13 V.

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33 Figure 2.44 Effect of slew-rate limiting on output sinusoidal waveforms.

34 Figure P2.2

35 Figure P2.8

36 Figure P2.16

37 Figure P2.22

38 Figure P2.25

39 Figure P2.30

40 Figure P2.31

41 Figure P2.32

42 Figure P2.34

43 Figure P2.35

44 Figure P2.43

45 Figure P2.46

46 Figure P2.47

47 Figure P2.49

48 Figure P2.50

49 Figure P2.51

50 Figure P2.59

51 Figure P2.62

52 Figure P2.68

53 Figure P2.69

54 Figure P2.70

55 Figure P2.71

56 Figure P2.77

57 Figure P2.78

58 Figure P2.84

59 Figure P2.85

60 Figure P2.86

61 Figure P2.89

62 Figure P2.92

63 Figure P2.93

64 Figure P2.102