Presentation is loading. Please wait.

Presentation is loading. Please wait.

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. MALVINO & BATES SEVENTH EDITION Electronic PRINCIPLES.

Published byGillian Booth Modified over 8 years ago

Similar presentations

Presentation on theme: "Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. MALVINO & BATES SEVENTH EDITION Electronic PRINCIPLES."— Presentation transcript:

1 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. MALVINO & BATES SEVENTH EDITION Electronic PRINCIPLES

2 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. JFETs Chapter 13

3 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Topics Covered in Chapter 13 Basic ideas Drain curves Transconductance curve Biasing in the ohmic region Biasing in the active region Transconductance

4 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Topics Covered in Chapter 13 (Continued) JFET amplifiers JFET analog switch Other JFET applications Reading data sheets JFET testing

5 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Junction field effect transistor (JFET) n pp Source Gate Drain V DD V GG G S D G S D Voltage controlled – the gate voltage controls the drain current

6 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. JFET Unipolar device (one polarity of charge carrier – no minority carriers) High input impedance Source and drain are interchangeable in most low-frequency applications Two diodes: gate-source and gate-drain For normal operation the gate-source diode is reverse-biased

7 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 0 V DS in Volts I D in mA -4 V 0 V -1 V -2 V -3 V V GS 510 15 20 2 4 6 8 10 Drain family of curves

8 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Drain curves With V GS = 0 the drain current is maximum at I DSS V P = the pinchoff voltage When V DS = V P the depletion layers almost touch With V DS > V P the JFET acts as a current source V GS(off) = -V P (Turns the JFET off)

9 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 0 V DS in Volts I D in mA -4 V 0 V -1 V -2 V -3 V V GS 510 15 20 2 4 6 8 10 V P = 4 volts I DSS Constant current region V GS(off)

10 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Ohmic region V P separates the active region from the ohmic region. The ohmic region is the almost vertical part of the drain curve. In this region, a JFET acts as a resistor. R DS = V P /I DSS

11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 0 V DS in Volts I D in mA -4 V 0 V -1 V -2 V -3 V V GS 510 15 20 2 4 6 8 10 Ohmic region When a JFET operates in the ohmic region, it has an ohmic resistance equal to V P / I DSS VPVP

12 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. The transconductance curve A graph of drain current versus gate- source voltage I D increases more rapidly as V GS approaches zero The normalized curve shows that I D equals one-quarter of maximum when V GS equals half of cutoff

13 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 0 2 4 6 8 10 -4 -3 -2 V GS in volts I D in mA Transconductance curve I D = I DSS 1- V GS V GS(off) ( ) 2

14 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. RDRD RGRG +V DD -V GG Gate bias is suitable for the ohmic region. I D(sat) = V DD RDRD Use 0 volts for V GS and I D(sat) << I DSS. +V DD RDRD R DS Equivalent circuit

15 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 0 V DS in Volts I D in mA -4 V 0 V -1 V -2 V -3 V V GS 510 15 20 2 4 6 8 10 V DD I D(sat) I D R DS Q Q point in the ohmic region

16 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Biasing in the active region Self-bias is used only with small-signal amplifiers because the Q point is unstable VDB can setup a stable Q point Two-source bias can swamp out variations in V GS and set up a stable Q point When supply voltages are low, current- source bias can produce a stable Q point

17 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Self-bias

18 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. RDRD R2R2 +V DD R1R1 RSRS Voltage-divider bias Gate bias is not suitable for the active region. V S = V G - V GS I D(sat) = V DD R D + R S V G - V GS RSRS I DQ =

19 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 0 V DS in Volts I D in mA -4 V 0 V -1 V -2 V -3 V V GS 510 15 20 2 4 6 8 10 V DD I D(sat) Q Q point in the active region

20 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Two-supply bias

21 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Current-source bias

22 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Transconductance Tells how effective the gate voltage is in controlling the drain current. g m = i d /v gs Common units for JFETs are the micromho (  mho) or the more modern microsiemen (  S). g m is the slope of the transconductance curve. g m0 is the maximum value and occurs at V GS = 0.

23 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 0 2 4 6 8 -4 -3 -2 V GS in volts I D in mA Transconductance curve g m = g m0 1- V GS V GS(off) ( ) Larger slope Max. slope g m0 Smaller slope

24 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. JFET amplifiers A common-source amplifier has a voltage gain of g m r d and the output is inverted An important JFET application is the source follower which has a high input resistance

25 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. RDRD R2R2 +V DD R1R1 RSRS v in RLRL v out Common-source amplifier r d = R D R L A V = g m r d

26 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. RDRD R2R2 +V DD R1R1 RSRS v in RLRL v out Source follower r s = R S R L A V = gmrsgmrs 1 + g m r s

27 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. JFET analog switch Transmits or blocks a small ac signal The JFET is biased into hard saturation or cutoff Shunt and series switches are used Series type switches have higher on-off ratios

28 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. v out v in V GS Shunt analog switch Series analog switch RDRD v out v in V GS RDRD R D >> R DS v in < 100 mV Better on-off ratio than the shunt switch

29 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Other JFET applications Multiplexers (ohmic) Chopper amplifiers (ohmic) Buffer amplifiers (active) Voltage controlled resistors (ohmic) AGC circuits (ohmic) Cascode amplifiers (active) Current sources (active) Current limiters (ohmic and active)

30 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. v out v in3 V3V3 RDRD v in2 V2V2 v in1 V1V1 Multiplexer

31 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Voltage-controlled resistance Operates in the ohmic region with V GS values between 0 and cutoff. Works well for ac signals of 200 mV PP or less. Small-signal resistance: r ds = V DS /I D As V GS becomes more negative, r ds increases. Both series and shunt operation can be used.

32 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cascode amplifier Low input capacitance allows the circuit to amplify high frequencies

33 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Current source Provides a fixed load current even though resistance changes

34 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Current limiting A JFET in series with the load keeps current limited to a safe value

35 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chopper amplifier Used to convert input dc to a square wave The peak value of this square wave equals V DC Chopper amps use conventional ac amplifiers Amplified output can be peak-detected to recover the amplified dc signal

36 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Buffer amplifier Isolates the preceding stage from the following stage Has high input impedance and low output impedance The source follower is an excellent buffer

37 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Automatic gain control

38 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Reading data sheets Review maximum ratings first Some ratings (i.e. V GS(OFF) ) may be omitted The large spread in JFET parameters justifies using ideal approximations for analysis and troubleshooting

39 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. JFET testing JFETs can be tested using an ohmmeter or DMM on the diode test range JFET current limits must not be exceeded Curve tracers and circuits can be used to display dynamic characteristics

Download ppt "Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. MALVINO & BATES SEVENTH EDITION Electronic PRINCIPLES."

Similar presentations

Electronic Devices Eighth Edition Floyd Chapter 8.

Electronic Devices Eighth Edition Floyd Chapter 8.
FET ( Field Effect Transistor)

FET ( Field Effect Transistor)
Transistors These are three terminal devices, where the current or voltage at one terminal, the input terminal, controls the flow of current between the.

Transistors These are three terminal devices, where the current or voltage at one terminal, the input terminal, controls the flow of current between the.
JUNCTION FIELD EFFECT TRANSISTOR(JFET)

JUNCTION FIELD EFFECT TRANSISTOR(JFET)
FET ( Field Effect Transistor)

FET ( Field Effect Transistor)
Field Effect Transistors Circuit Analysis EE314 HP PA8000 Fujitsu 68903 Fairchild Clipper C100.

Field Effect Transistors Circuit Analysis EE314 HP PA8000 Fujitsu Fairchild Clipper C100.
Week 9a OUTLINE MOSFET ID vs. VGS characteristic

Week 9a OUTLINE MOSFET ID vs. VGS characteristic
Electronics Principles & Applications Sixth Edition Chapter 7 More About Small-Signal Amplifiers (student version) ©2003 Glencoe/McGraw-Hill Charles A.

Electronics Principles & Applications Sixth Edition Chapter 7 More About Small-Signal Amplifiers (student version) ©2003 Glencoe/McGraw-Hill Charles A.
Principles & Applications

Principles & Applications
© 2012 Pearson Education. Upper Saddle River, NJ, 07458. All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Electronic Devices Ninth.

© 2012 Pearson Education. Upper Saddle River, NJ, All rights reserved. Electronic Devices, 9th edition Thomas L. Floyd Electronic Devices Ninth.
Field Effect Transistors Topics Covered in Chapter 30 30-1: JFETs and Their Characteristics 30-2: Biasing Techniques for JFETs 30-3: JFET Amplifiers 30-4:

Field Effect Transistors Topics Covered in Chapter : JFETs and Their Characteristics 30-2: Biasing Techniques for JFETs 30-3: JFET Amplifiers 30-4:
FET ( Field Effect Transistor)

FET ( Field Effect Transistor)
ANALOGUE ELECTRONICS I

ANALOGUE ELECTRONICS I
Chapter 13 Small-Signal Modeling and Linear Amplification

Chapter 13 Small-Signal Modeling and Linear Amplification
Bipolar Junction Transistors

Bipolar Junction Transistors
Chapter 28 Basic Transistor Theory. 2 Transistor Construction Bipolar Junction Transistor (BJT) –3 layers of doped semiconductor –2 p-n junctions –Layers.

Chapter 28 Basic Transistor Theory. 2 Transistor Construction Bipolar Junction Transistor (BJT) –3 layers of doped semiconductor –2 p-n junctions –Layers.
Semiconductor Devices III Physics 355. Transistors in CPUs Moore’s Law (1965): the number of components in an integrated circuit will double every year;

Semiconductor Devices III Physics 355. Transistors in CPUs Moore’s Law (1965): the number of components in an integrated circuit will double every year;
09/16/2010© 2010 NTUST Today Course overview and information.

09/16/2010© 2010 NTUST Today Course overview and information.
Chapter 17 Electronics Fundamentals Circuits, Devices and Applications - Floyd © Copyright 2007 Prentice-Hall Chapter 17.

Chapter 17 Electronics Fundamentals Circuits, Devices and Applications - Floyd © Copyright 2007 Prentice-Hall Chapter 17.
© The McGraw-Hill Companies, Inc. 2000 McGraw-Hill 1 PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING THIRD EDITION G I O R G I O R I Z Z O N I 9.

© The McGraw-Hill Companies, Inc McGraw-Hill 1 PRINCIPLES AND APPLICATIONS OF ELECTRICAL ENGINEERING THIRD EDITION G I O R G I O R I Z Z O N I 9.

Similar presentations

Ads by Google