Electronic devices-and-circuit-theory-10th-ed-boylestad-chapter-8
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This chapter discusses FET amplifiers. It describes the common FET configurations including common-source, common-gate, and common-drain. It provides the small-signal models and defines terms like transconductance. It then gives the input and output impedances and voltage gain calculations for each configuration. Examples of biased circuits are also presented along with a troubleshooting guide.
Electronic devices-and-circuit-theory-10th-ed-boylestad-chapter-8
- 1. Chapter 8: FET Amplifiers
- 2. Introduction FETs provide: Excellent voltage gain High input impedance Low-power consumption Good frequency range Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 2
- 3. FET Small-Signal Model Transconductance The relationship of a change in ID to the corresponding change in VGS is called transconductance Transconductance is denoted gm and given by: D m I g = GS V Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 3
- 4. Graphical Determination of gm Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 4
- 5. Mathematical Definitions of gm D I m V GS g = ､ ･ｦ ｡ DSS 2I = ｢｣ GS m V P P V 1 V g DSS m0 V P 2I g = ｡ ､ Where VGS =0V ･ｦ = ｢｣ GS m m0 V P V g g 1 D DSS V GS 1 = P I I V V I Where D DSS m0 GS 1 g g = m m0 I P g V = Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 5
- 6. FET Impedance Input impedance: p Zi = 立 Output Impedance: Z = r = 1 o d y yos V where: d I GS V constant DS D V r = = yos= admittance parameter listed on FET specification sheets. Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 6
- 7. FET AC Equivalent Circuit Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 7
- 8. Common-Source (CS) Fixed-Bias Circuit The input is on the gate and the output is on the drain There is a 180属 phase shift between input and output Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 8
- 9. Calculations Input impedance: Zi = RG p Output p impedance: Zo = RD || rd Z R o D r 10R d D Voltage gain: o A m d D g (r || R ) V v = = V i v g R rd 10RD m D o V i V A = = Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 9
- 10. Common-Source (CS) Self-Bias Circuit This is a common-source amplifier configuration, so the input is on the gate and the output is on the drain There is a 180属 phase shift between input and output Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 10
- 11. Calculations Input impedance: Z Zi = R RG p Output p impedance: Zo = rd || RD Z R o D r 10R d D Voltage gain: Av = gm(rd || RD) Av = gmRD rd 10RD Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 11
- 12. Common-Source (CS) Self-Bias Circuit Removing Cs affects the gain of the circuit. Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 12
- 13. Calculations Input impedance: Zi i = G RG Output impedance: Z R o D r 10R d D Voltage gain: Vo gmRD A = = R R D S d m S i v r V 1 g R + + + Vo o m gmRD D A r 10(R R ) v 1 g R d D S m S i g V + + = = Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 13
- 14. Common-Source (CS) Voltage-Divider Bias This is a common-source amplifier configuration, so the input is on the gate and the output is on the drain. Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 14
- 15. Impedances Input impedance: Zi = R1 || R2 Output impedance: Zo = rd || RD Z R o D r 10R d D Voltage gain: Av = gm(rd || RD ) Av = gmRD rd 10RD Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 15
- 16. Source Follower (Common-Drain) Circuit In a common-drain amplifier configuration, the input is on the gate, but the output is from the source. There is no phase shift between input and output. Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 16
- 17. Impedances Input impedance: Z Zi = R RG Output impedance: Z = r || R || 1 m o d S g 1 Z R || rd 10RS m o S g Voltage g (r || R ) m d S gain: = = v + 1 g (r || R ) V o V A m d S i V A = = + v 1 g R d r 10 m S m S o i g R V Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 17
- 18. Common-Gate (CG) Circuit The input is on the source and the output is on the drain. There is no phase shift between input and output. Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 18
- 19. Calculations Input impedance: ､ ･ｦ ｡ + ｢｣ r + R = d D i S 1 g r m d Z R || 1 Z R || rd 10RD m i S g Output impedance: Zo = RD || rd Voltage o D rd 10 Z R ､ ･ｦ ｡ ｢ ｣ + D R = = ｦ A d v = m D rd 10RD g R m D gain: o r V A g R ､ ･ｦ ｡ + ｢｣ D R d i v r 1 V Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 19
- 20. D-Type MOSFET AC Equivalent Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 20
- 21. E-Type MOSFETAC Equivalent gm and rd can be found in the specification sheet for the FET. Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 21
- 22. Common-Source Drain-Feedback There is a 180属 phase shift between input and output. Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 22
- 23. Calculations Input impedance: R r || R F d D 1 g (r || R ) Z m d D i + + = R ||R 10R F i R Z RF rd RD ,rd 10RD >> + 1 g R m D Output impedance: p p Zo = RF || rd ||RD Zo RD RF >>rd || RD , rd 10RF d D d D Voltage gain: Av = gm(RF || rd || RD ) Av gmRD RF>>rd||RD,rd10RD Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 23
- 24. Common-Source Voltage-Divider Bias Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 24
- 25. Calculations Input impedance: Zi=R1|| R2 O t Output t i d impedance: Zo = rd || RD Zo RD rd 10 Z R Voltage gain: Av = gm(rd || RD) A g R Av gmRD rd 10RD Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 25
- 26. Summary Table Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky more 26
- 27. Summary Table Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 27
- 28. Troubleshooting Check the DC bias voltages: If not correct check power supply, resistors, FET. Also check to ensure that the coupling capacitor between amplifier stages is OK. . Check the AC voltages: If not correct check FET, capacitors and the loading effect of the next stage Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 28
- 29. Practical Applications Three-Channel Audio Mixer Silent Switching Phase Shift Networks Motion Detection System Copyright 息2009 by Pearson Education, Inc. Upper Saddle River, New Jersey 07458 All rights reserved. Electronic Devices and Circuit Theory, 10/e Robert L. Boylestad and Louis Nashelsky 29