"Chapter 1 - The Op Amp's Place in the World" - HTL Wien 10

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Stability and Feedback Capacitance 8-12 quency axis, lowering the circuit stability. Eventually it interacts with the pole contained in Z, 1/τ 2, and instability results. The effects of stray capacitance on CFA closed-loop performance are shown in Figure 8–8. Figure 8–8. Effects of Stray Capacitance on CFAs Amplitude (3 dB/div) AMPLITUDE vs FREQUENCY CF = 2 pF No Stray Capacitance 1 10 100 f – Frequency – MHz CIN = 2 pF Notice that the introduction of C G causes more than 3 dB peaking in the CFA frequency response plot, and it increases the bandwidth about 18 MHz. Two picofarads are not a lot of capacitance because a sloppy layout can easily add 4 or more picofarads to the circuit. 8.9 Stability and Feedback Capacitance When a stray capacitor is formed across the feedback resistor, the feedback impedance is given by Equation 8–31. Equation 8–32 gives the loop gain when a feedback capacitor has been added to the circuit.
Z F A R F 1 R F C F s Z1 R F C F s R F1 R B R FR G1 R B R F R G C F s Compensation of CF and CG Current-Feedback Op Amp Analysis (8–31) (8–32) This loop gain transfer function contains a pole and zero, thus, depending on the pole/zero placement, oscillation can result. The Bode plot for this case is shown in Figure 8–9. The original and composite curves cross the 0-dB axis with a slope of –40 dB/decade, so either curve can indicate instability. The composite curve crosses the 0-dB axis at a higher frequency than the original curve, hence the stray capacitance has added more phase shift to the system. The composite curve is surely less stable than the original curve. Adding capacitance to the inverting input node or across the feedback resistor usually results in instability. R B largely influences the location of the pole introduced by C F, thus here is another case where stray capacitance leads to instability. AMPLITUDE (dB Ω ) Figure 8–9. Bode Plot with C F 0 fZ 20LOGIZI – 20LOGIZF(1 + ZB/ZFIIZG)I fP POLE/ZERO Curve Composite Curve LOG(f) Figure 8–8 shows that C F = 2 pF adds about 4 dB of peaking to the frequency response plot. The bandwidth increases about 10 MHz because of the peaking. C F and C G are the major causes of overshoot, ringing, and oscillation in CFAs, and the circuit board layout must be carefully done to eliminate these stray capacitances. 8.10 Compensation of C F and C G When C F and C G both are present in the circuit they may be adjusted to cancel each other out. The stability equation for a circuit with C F and C G is Equation 8–33. 8-13
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Operational Amplifier Chapter 1: Th
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1-2 problem. It seems that circuits
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1-4 you are looking in the wrong pl
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Laws of Physics 2-2 V IR (2-1) In
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Current Divider Rule 2-4 put voltag
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Thevenin’s Theorem 2-6 V theorem
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Superposition 2.6 Superposition 2-8
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Transistor Amplifier 2-10 I C I B
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Transistor Amplifier 2-12 approxima
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Ideal Op Amp Assumptions 3-2 a hard
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The Inverting Op Amp 3-4 in a curre
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The Differential Amplifier 3.5 The
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Complex Feedback Networks 3-8 Break
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Capacitors Figure 3-10. Low-Pass Fi
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3-12
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Single Supply versus Dual Supply 4-
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Circuit Analysis 4-4 VREF VIN Figur
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Circuit Analysis 4-6 Four op amps w
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Simultaneous Equations 4.3 Simultan
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Simultaneous Equations 4-10 VOUT V
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Simultaneous Equations 4-12 VIN = 0
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Simultaneous Equations 4-14 m R F
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Simultaneous Equations 4.3.3 Case 3
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Simultaneous Equations 4-18 - Input
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Simultaneous Equations 4-20 |b| V
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Summary 4.4 Summary 4-22 Single-sup
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Block Diagram Math and Manipulation
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Block Diagram Math and Manipulation
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Feedback Equation and Stability 5.3
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Bode Analysis of Feedback Circuits
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Page 64 and 65: Loop Gain Plots are the Key to Unde
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Page 68 and 69: References 5-16 M tangent 1 (2) (
Page 70 and 71: Review of the Canonical Equations 6
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Page 82 and 83: Internal Compensation 7-4 Damping R
Page 84 and 85: Internal Compensation AVD - Large-S
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Page 88 and 89: Dominant-Pole Compensation 7-10 VTH
Page 90 and 91: Gain Compensation 7-12 VOUT VIN a
Page 92 and 93: Lead Compensation 7-14 transfer fun
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Page 96 and 97: Lead-Lag Compensation 7-18 FHASE (A
Page 98 and 99: Comparison of Compensation Schemes
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Page 102 and 103: Development of the Stability Equati
Page 104 and 105: The Noninverting CFA Figure 8-4. No
Page 106 and 107: The Inverting CFA 8-6 The current e
Page 108 and 109: Stability Analysis 8-8 The plot in
Page 110 and 111: Selection of the Feedback Resistor
Page 114 and 115: Summary 8.11 Summary 8-14 A Z1 R
Page 116 and 117: Precision 9.2 Precision 9-2 The lon
Page 118 and 119: Bandwidth 9-4 A aR G R F R G (9-2
Page 120 and 121: Stability 9.4 Stability 9-6 Substit
Page 122 and 123: Equation Comparison 9-8 R G = 100
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Page 126 and 127: Characterization 10-2 Noise Signal
Page 128 and 129: Types of Noise 10.2.5 Noise Units 1
Page 130 and 131: Types of Noise 10-6 Shot noise is
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Page 134 and 135: Noise Colors Figure 10-4. Avalanche
Page 136 and 137: Op Amp Noise 10.4.3 Red/Brown Noise
Page 138 and 139: Op Amp Noise 10-14 E n Square it.
Page 140 and 141: Op Amp Noise 10.5.4 Inverting Op Am
Page 142 and 143: Op Amp Noise 10.5.6 Differential Op
Page 144 and 145: Putting It All Together 10-20 Vn Vn
Page 146 and 147: Putting It All Together 10-22 volta
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Page 150 and 151: Operational Amplifier Parameter Glo
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Additional Parameter Information 11
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12-2 The ADC selection is based on
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12-4 (A) 4 V 3 V ADC 0 V Sensor Out
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12.2 Transducer Types 12-6 This is
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12-8 some value, and R X is switche
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12-10 Resolvers and synchros are po
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12-12 6) Scan the transducer and AD
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12-14 the worst case excursions of
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Table 12-3. Op Amp Selection 12-16
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12-18 this yields m = 16.16. The re
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12-20 0.97R 1 VREF(MIN) VREF 50 m
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12-22 ply contribution is reduced b
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12-24
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Wireless Systems 13-2 Signal @ - 10
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Wireless Systems 13-4 900 MHz Figur
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Selection of ADCs/DACs 13.3 Selecti
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Selection of ADCs/DACs 13-8 Therefo
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Factors Influencing the Choice of O
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Anti-Aliasing Filters 13-12 anti-al
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Communication D/A Converter Reconst
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External Vref Circuits for ADCs/DAC
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High-Speed Analog Input Drive Circu
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High-Speed Analog Input Drive Circu
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References 13.9 References 13-22 [1
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Understanding the D/A Converter and
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Understanding the D/A Converter and
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D/A Converter Error Budget 14-6 rat
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D/A Converter Error Budget 14-8 The
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D/A Converter Errors and Parameters
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Compensating For DAC Capacitance 14
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Increasing Op Amp Buffer Amplifier
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Increasing Op Amp Buffer Amplifier
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14-24
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Requirements for Oscillation 15-2 u
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Gain in the Oscillator 15-4 The fre
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Active Element (Op Amp) Impact on t
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Analysis of the Oscillator Operatio
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Sine Wave Oscillator Circuits 15-10
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References 15.8 References 15-22 [1
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Fundamentals of Low-Pass Filters 16
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Low-Pass Filter Design 16-12 1st or
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Low-Pass Filter Design Example 16-1
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Low-Pass Filter Design 16-16 In ord
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Low-Pass Filter Design 16.3.2.2 Mul
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Low-Pass Filter Design Second Filte
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High-Pass Filter Design 16-22 |A|
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High-Pass Filter Design 16-24 To di
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High-Pass Filter Design 16-26 Throu
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Band-Pass Filter Design 16-28 |A| [
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Band-Pass Filter Design 16-30 The g
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Band-Pass Filter Design 16-32 out a
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Band-Pass Filter Design 16-34 After
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Band-Rejection Filter Design 16-36
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All-Pass Filter Design 16-42 2 i
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All-Pass Filter Design 16.7.1 First
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All-Pass Filter Design 16-46 V IN f
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Practical Design Hints 16-48 low-pa
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Practical Design Hints V IN 16-50 C
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Practical Design Hints 16-52 If thi
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Practical Design Hints 16-54 f T 1
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Filter Coefficient Tables Table 16-
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16-64
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General Considerations 17.1.3 Noise
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PCB Mechanical Construction 17-4 Te
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PCB Mechanical Construction 17.2.2.
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Grounding 17-8 DIGITAL + DIGITAL -
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Grounding 17-10 CONNECTOR POWER SUP
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The Frequency Characteristics of Pa
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Decoupling 17-20 For example, a 0.4
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Decoupling 17-22 EQUIVALENT SERIES
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Packages 17.7 Packages 17-24 N1 IN-
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Packages 17-26 IN1 + OUT1 IN2 IN3 O
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Summary 17-28 HALF SUPPLY GOOD _ +
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17-30
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Introduction 18-2 swing at V CC = 5
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Dynamic Range 18-4 VIN VnR Figure 1
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Input Common-Mode Range 18-6 sible
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Input Common-Mode Range 18-8 VCC GN
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Input Common-Mode Range 18-10 V µ
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Shutdown and Low Current Drain 18-1
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Transducer to ADC Analog Interface
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DAC to Actuator Analog Interface 18
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DAC to Actuator Analog Interface 18
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Comparison of Op Amps 18-20 When DA
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Summary 18.11 Summary 18-22 Always
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"Chapter 1 - The Op Amp's Place in the World" - HTL Wien 10

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