1. 1 References: A. Sedra and K.C. Smith, Microelectronic Circuits, © Oxford University Press, 5/e, 2004 A.R. Hambley, Electronics, © Prentice Hall, 2/e, 2000 Introduction to Amplifiers

2. 2 The Electronic Amplifier

3. Figure 1.16 Input waveform and corresponding output waveforms. 3 Amplifier’s Waveforms

4. Fig. 1.13 An amplifier transfer characteristic that is linear except for output saturation. 4 Amplifier’s Transfer Function (TF): Ideal Case

5. Fig. 1.14 (a) An amplifier transfer characteristic that shows considerable nonlinearity. (b) To obtain linear operation the amplifier is biased as shown, and the signal amplitude is kept small. 5 Amplifier’s TF: Non-ideal Case

6. Figure 1.22 The power supply delivers power to the amplifier from several constant voltage sources. Where does amplification come from ? 6

7. Figure 1.23 Illustration of power balance. No free lunch !!! 7

8. Amplifier models Voltage amplifier Current amplifier Transconductance amplifier Transresistance amplifier For a given amplifier, a particular model may be preferable. However, any of the four can be used to model the amplifier

9. Figure 1.17 Model of an electronic amplifier, including input resistance R i and output resistance R o. Voltage Amplifier Model 9

10. Figure 1.25 Current-amplifier model. Current Amplifier Model 10

11. Figure 1.28 Transconductance-amplifier model. Transconductance Amplifier Model 11

12. Figure 1.30 Transresistance-amplifier model. Transresistance Amplifier Model 12

13. Figure 1.32 If we want to sense the open-circuit voltage of a source, the amplifier should have a high input resistance, as in (a). To sense short-circuit current, low input resistance is called for, as in (b). Voltage and Current Sources. Practical Considerations: R in 13

14. Figure 1.33 If the amplifier output impedance R o is much less than the (lowest) load resistance, the load voltage is nearly independent of the number of switches closed. Practical Considerations: R o 14

15. Figure 1.34 To avoid reflections, the amplifier input resistance R i should equal the characteristic resistance Z o of the transmission line. Effect of interconnections 15

16. Keeping AC (signal) and DC (power supply) away from each other vsvs RsRs load amplifier DC

17. Figure 1.39 Gain versus frequency for a typical amplifier showing the upper and lower half-power (3-dB) frequencies (f H and f L ) and the half-power bandwidth B. A Typical Amplifier’s Frequency Response 17

18. Decibel Notation Power Gain Voltage Gain Current Gain

19. Figure 1.19 Cascade connection of two amplifiers. Multistage Amplifiers 19

20. How do we model a multiple stage amplifier? 20

21. Figure 1.37 Capacitive coupling prevents a dc input component from affecting the first stage, dc voltages in the first stage from reaching the second stage, and dc voltages in the second stage from reaching the load. Coupling multistage amplifiers 21

22. Figure 1.38 Capacitance in parallel with the signal path and inductance in series with the signal path reduce gain in the high-frequency region. Parasitic effects 22

23. Figure 1.36 Gain versus frequency. Amplifier’s frequency response 23

24. Figure 1.40 Gain magnitude versus frequency for a typical bandpass amplifier. A band pass amplifier 24

25. Figure 1.41 Input pulse and typical ac-coupled broadband amplifier output. Effect of having a band limited frequency response 25

26. Figure 1.42 Rise time of the output pulse. (Note: No tilt is shown. When tilt is present, some judgement is necessary to estimate the amplitude V f ). Zooming-in the output pulse 26

27. Figure 1.43 Differential amplifier with input sources. The Differential Amplifier 27

28. Why do we need differential amplifiers ?

29. Figure 1.47 Setup for measuring differential gain. A d = v o /v id. Differential Gain 29

30. Figure 1.46 Setup for measurement of common-mode gain. Common-mode Gain 30