1 Slides taken from: A.R. Hambley, Electronics, © Prentice Hall, 2/e, 2000 A. Sedra and K.C. Smith, Microelectronic Circuits, © Oxford University Press, 4/e, 1999 Operationa l Amplifiers
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1
Slides taken from:
A.R. Hambley, Electronics, © Prentice Hall, 2/e, 2000
A. Sedra and K.C. Smith, Microelectronic Circuits, © Oxford University Press, 4/e, 1999
Operational Amplifiers
2Figure 2.1 Circuit symbol for the op amp.
Operational Amplifier Symbol
3Figure 2.3 Op-amp symbol showing power supplies.
Operational Amplifier Symbol
4
Internal Structure of Op Amps
+
-
vid
vo
+
-
TranscoductanceDifferentialAmplifier
High GainVoltage
Amplifier
UnityGain
Buffer
C
5Figure 2.2 Equivalent circuit for the ideal op amp. AOL is very large (approaching infinity).
The ideal OA
6
The ideal OA
Infinite input impedance Infinite open-loop gain for the differential input Zero gain for the common mode signal Zero output impedance Infinite Bandwidth
7
The OA Transfer CurvevO
vid
8
Feedback
Negative FeedbackPart of the output signal is returned to the input
in opposition to the source signal
Positive FeedbackThe signal returned from the output to the input
aids the original source signal
9
Figure 2.5 Inverting amplifier.
The Inverting Amplifier
10Fig. 2.5 Analysis of the inverting configuration
Analysis of the Inverting Amplifier
11Figure 2.6 An inverting amplifier that achieves high gain with a smaller range of resistor values than required for the basic inverter.
Another Inverting Amplifier
12Figure 2.11 Non-inverting amplifier.
The Non-inverting Amplifier
13Figure 2.12 Voltage Follower.
The Voltage Follower
14
Figure 2.14 Difference amplifier.
Difference Amplifier (1)
15
Fig. 2.22 Application of superposition to the analysis of the difference amplifier
Difference Amplifier (2)
16
Fig. 2.23 Finding the input resistance of the difference amplifier.
Difference Amplifier (3)
17
Figure 2.7 Summing amplifier.
Summing Amplifier
18
Figure 2.13 Inverting or non-inverting amplifier.
Inverting/Non-Inverting Amplifier (1)
19
Inverting/Non Inverting Amplifier (2)
20
Inverting/Non inverting Amplifier (3)
21Figure 2.10a Schmitt trigger circuit.
A positive feedback’s example: Schmitt Trigger
22Figure 2.10b Schmitt trigger circuit and waveforms.
A positive feedback’s example: Schmitt Trigger
23Figure 2.20 If low-value resistors are used, an impractically large current is required.
Practical Design Considerations:Non-inverting Amplifier
24Figure 2.21 If very high value resistors are used, stray capacitance can couple unwanted signals into the circuit.
Practical Design Considerations:Non-inverting Amplifier
25
Figure 2.22 To attain large input resistance with moderate resistances for an inverting amplifier we cascade a voltage follower with an inverter.
Practical Design Considerations:Inverting Amplifier
26
OP-AMP Imperfections
Non-linearity in the range of operation Finite input impedance and non-zero output
impedance Limited bandwidth and gain Saturation Output Current Limit Slew Rate non linearity DC offset
27Figure 2.25 Bode plot of open-loop gain for a typical op amp.
Gain and Bandwidth Limitations
28Figure 2.26 Non-inverting amplifier.
Effect of the gain and bandwidth limitations.
29Figure 2.27 Bode plots for the non-inverting amplifier.
Effect of the gain and bandwidth limitations.
30Figure 2.28 For a real op amp, clipping occurs if the output voltage reaches certain limits.
Saturation
31
Output Current Limit
The current that an op amp can supply to a load is limited (typically +/-25 mA)
If a small-value load draw a current outside the limit, the output waveform becomes clipped
32Figure 2.30 Output for R1=1Kohm R2= 3Kohm RL = 10kohm and Vs max = 5V.
Max Output Voltage Swing
33
Slew Rate Limitation
The output voltage of an op amp cannot change in magnitude at a rate exceeding the slew rate limit
34Figure 2.31 Output for RL = 10kohm and vs(t) = 2.5 sin (105 t).
Effect of Slew Rate Limitation
35
Effect of Slew Rate Limitation
Fig. 2.29 (a) Unity-gain follower. (b) Input step waveform. (c) Linearly rising output waveform obtained when the amplifier is slew-rate limited.
36
Effect of Slew Rate Limitation
Full-power bandwidth fFPB: range of frequencies for which the op amp can
produce an undistorted sinusoidal output with peak amplitude equal to the guaranteed maximum output voltage.
37
DC Imperfections
Input Bias Current
Input Offset Current
Input Offset Voltage
38Figure 2.33 Current sources and a voltage source model the dc imperfections of an op amp.
Modeling DC Imperfections
39
Modeling DC Imperfections
40
Modeling DC Imperfections
41
Modeling DC Imperfections
42
Modeling DC Imperfections
43Figure 2.35 Adding the resistor R to the inverting amplifier circuit causes the effects of bias currents to cancel.
Canceling the Effects of Bias Currents
44Figure 2.36 Non-inverting amplifier, including resistor R to balance the effects of the bias currents.
Canceling the Effects of Bias Currents
45
Figure 2.46 Unity-gain amplifiers.
Common OA Circuits: unity gain amplifiers
46Figure 2.47 Inverting amplifier.
Common OA Circuits: Inverting Amplifier
47Figure 2.48 Ac-coupled inverting amplifier.
Common OA Circuits: AC coupled inverting amplifier
48Figure 2.49 Summing amplifier.
Common OA Circuits: Summing Amplifier
49Figure 2.50 Non-inverting amplifier. This circuit approximates an ideal voltage amplifier.
Common OA Circuits: Non-Inverting Ampl.
50Figure 2.51 Ac-coupled non-inverting amplifier.
Common OA Circuits: AC coupled non inverting amplifier
51Figure 2.52 Ac-coupled voltage follower with bootstrapped bias resistors.
AC coupled follower (1)
52
AC coupled follower (2)
53
AC coupled follower (3)
54
AC coupled follower (4)
55
AC coupled follower (5)
56Figure 2.53 Difference amplifier.
Common OA Circuits: Difference Amplifier
57Figure 2.54 Instrumentation-quality differential amplifier.
Common OA Circuits: Instrumentation Difference Amplifier
58Figure 2.55 Voltage-to-current converter (transconductance amplifier).
Common OA Circuits: Voltage/Current Converter
59Figure 2.56 Voltage-to-current converter with grounded load.
Common OA Circuits: Voltage/Current Converter (Inverting)
60Figure 2.56 Voltage-to-current converter with grounded load.
Voltage/Current Converter (Non Inverting)(step 1)
61
Voltage/Current Converter (non Inverting)(step 2)
62
Voltage/Current converter (step 3)
63Figure 2.57 Current-to-voltage converter (transresistance amplifier).
Common OA Circuits: Current/Voltage Converter
64Figure 2.58 Current amplifier.
Common OA Circuits: Current Amplifier
65Figure 2.59 Variable-gain amplifier.
Common OA Circuits: Variable Gain Ampl.
66
Common OA Circuits: Filters
-
+
+
-+
-
Z2
Z1
67Figure 2.60 Integrator Filter.
Common OA Circuits: Integrator
68Figure 2.63 Differentiator Filter.
Common OA Circuits: Derivator
69Figure 2.64c Comparative Bode plots.
OA’s Bode Plot
70Figure 2.64a Comparative Bode plots.
Integrator’s Bode Plot
71Figure 2.64b Comparative Bode plots.
Differentiator’s Bode Plot
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