Frequently Asked Questions

from

The Art of Electronics

by

Paul Horowitz and Winfield Hill

AMiglani2014@gmail.com

Last Updated: November 13, 2014

Contents

1 Foundations 2

2 Transistors 3

3 Field-Effect Transistors 4

4 Feedback and Operational Amplifiers 54.1 Introduction to feedback . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54.2 Operational Amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54.3 Golden Rules . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54.4 Inverting Amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54.5 Non-inverting Amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54.6 Followers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54.7 Current Sources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54.8 Basic Cautions for Op-Amp Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54.9 Linear Cicuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64.10 Nonlinear Circuits . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64.11 Departure from ideal op-amp performance . . . . . . . . . . . . . . . . . . . . . . . . . . . 64.12 Effects of op-amp limitations on circuit behaviors . . . . . . . . . . . . . . . . . . . . . . . 64.13 Low-power and programmable op-amps . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74.14 Logarithmic amplifier . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74.15 Active Peak Detector . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74.16 Sample-and-Hold . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74.17 Active Clamp . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74.18 Absolute-value Circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74.19 Integrators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74.20 Differentiators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74.21 Biasing Single-Supply AC Amplifiers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74.22 Single Supply Op-Amps . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74.23 Comparators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 74.24 Schmitt Trigger . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

5 Active Filters and Oscillators 8

1

Chapter 1

Foundations

2

Chapter 2

Transistors

3

Chapter 3

Field-Effect Transistors

4

Chapter 4

Feedback and Operational Amplifiers

4.1 Introduction to feedback

Q 1: What are the advantages of negative feedback? Ans 1

4.2 Operational Amplifiers

4.3 Golden Rules

Q 2: How much differential input voltage is necessary to swing the output to its maximum value? Ans2

Q 3: How much current does an op amp draw? Ans 3

4.4 Inverting Amplifiers

4.5 Non-inverting Amplifiers

4.6 Followers

4.7 Current Sources

4.8 Basic Cautions for Op-Amp Circuits

Q 4: Why should op-amp work in active region? Explain if it leaves active region. Ans 4

Q 5: When will happen when an op-amp with a negative feedback has inverting and non-inverting inputsare mixed-up? Ans 5

Q 6: Why must an op-amp circuit have feedback at dc? Ans 6

Q 7: What would happen if we put a capacitor in series between the output and the inverting input?Ans 7

Q 8: What would happen if large input current flow in an op-amp? Ans 8

Q 9: Why should the maximum voltage difference between inverting and non-inverting inputs be limitedto as little as 5V in either polarity? Ans 9

5

4.9 Linear Cicuits

Q 10: Why is this mandatory to use a resistor to ground in case of op-amp with ac-coupled inputs? Ans10

Q 11: Is it necessary to have equal resistance for each of inputs to the summing amplifier? Ans 11

Q 12: What does happens when output of a non-inverting amplifier is fed to the follower with push-pullconfiguration? Explain complete analysis of this circuit? Ans 12

Q 13: Design an 10V regulator using an op-amp as comparator and darlington configuration with powertransistors. Ans 13

Q 14: Why are ripples are reduced if we bias the zener, which provides reference voltage, with a currentsource instead of resistive network? Ans 14

4.10 Nonlinear Circuits

Q 15: Give possible configurations for rectification of signals smaller than a diode drop. Also analyze thecircuit. Ans 15

4.11 Departure from ideal op-amp performance

Q 16: What is input current and what are the side-effects of this? Ans 16

Q 17: What is input offset current and what are the side-effects of this? Ans 17

Q 18: What is input impedance and how is this measured? Ans 18

Q 19: Why should input impedance be high? Ans 18

Q 20: What is the (dc) common-mode input range and what does happen when input goes beyond thisrange? Ans 19

Q 21: What is the differential-mode input range? Ans 20

Q 22: Explain the importance of output impedance and relationship between output swing vs. loadresistance. Ans 21

Q 23: What is the effect of compensation on slew rate? Ans 22

Q 24: In low-drift and high-precision instrumentation op-amps why should the load be kept very highabove 10K? Ans 23

4.12 Effects of op-amp limitations on circuit behaviors

Q 25: What is the relationship between open-loop gain (A0) and gain of feedback network (β)? Ans 24

Q 26: What is the relationship between transition frequency and 3-dB frequency? Ans 25

Q 27: Plot the variation in peak-to-peak output voltage with respect to frequency and explain the phe-nomenon of 1/f drop-off of this characteristics. Give relationship between peak-to-peak voltageand slew rate. Ans 26

Q 28: For precision applications, why is this a good idea to avoid large output currents? Ans 27

Q 29: What is the meaning of offset voltage at the output? Ans 28

Q 30: Explain how input bias current creates problem at the output. Provide three remedies in terms ofinput impedance at both inverting and non-inverting terminals, resistance of feedback network ordc gain to unity. Ans 29

6

Q 31: What is the typical range of input current in case of op-amp with BJT and FET/MOSFET? Ans30

Q 32: List down the trade-offs associated with impedance (high and low) of feedback networks. Ans 31

Q 33: List down the trade-offs associated with quiescent current (high and low) of op-amp. Ans 32

4.13 Low-power and programmable op-amps

Q 34: What are low-power and programmable op-amps? Ans 33

4.14 Logarithmic amplifier

4.15 Active Peak Detector

4.16 Sample-and-Hold

4.17 Active Clamp

4.18 Absolute-value Circuit

4.19 Integrators

4.20 Differentiators

4.21 Biasing Single-Supply AC Amplifiers

4.22 Single Supply Op-Amps

4.23 Comparators

4.24 Schmitt Trigger

Q 35: What is the purpose of using positive feedback? What are the differneces in the operations ofschmitt trigger without feedback? Why should not we use negative feedback in it? Ans 34

Q 36: What is the purpose of using two thresholds in the schmitt trigger? Ans 35

Q 37: How does a capacitor increase the switching speed of the schmitt trigger? Ans 36

7

Chapter 5

Active Filters and Oscillators

Q 38: Is this possible to cascade multiple filter stages to get close to ideal low pass filter? Explain interms of trade-off between fall-off and knee of the response. Ans 37

Q 39: What is the effect of cascading several RC sections on 3-dB frequency? Explain in terms of roll-offfrequencies. Ans 37

Q 40: Give definition 3-dB frequency, breakpoint frequency, transition frequency etc. Ans 37

Q 41: What is the effect of using inductor in filters on fall-off, knee etc? Ans 37

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