Field Effect Transistor (FET)

Concept of Field Effect Transistors (channel width modulation), Gate isolation types, JFET Structure and characteristics, MOSFET Structure and characteristics, depletion and enhancement type; CS, CG, CD configurations; CMOS: Basic Principles

1. Mr.Darwin Nesakumar A Assistant Professor/ECE RMKEC Unit - III Field Effect Transistors

2. Contents Introduction Basic Structure of JFET Symbol Construction of JFET JFET Characteristics and Parameters MOSFET Structure and characteristics Depletion and enhancement type IGBT  

3. Contents CS configurations CG configurations CD configurations CMOS: Basic Principles Inverter

4. Introduction FETs are unipolar devices FET is a Voltage-controlled device High input resistance

5. FET Types

6. JFET Construction JFET is a three-terminal device with one terminal capable of controlling the current between the other two There are two types of JFETs n-channel p-channel A JFET consists of a or silicon bar containing two junctions at the sides  

7. JFET Construction    

8. Source: It is the terminal through which majority carriers enter the bar. Drain: It is the terminal through which majority carriers leave the bar i.e. they are drained out from this terminal. Gate: These are two internally-connected heavily-doped impurity regions which form two P-N junctions. Channel: It is the space between two gates through which majority carriers pass from source-to-drain JFET Construction

9. Construction of JFET  

10. Operation of JFET  

11. Operation of JFET   ( i ) When and  

12. Operation of JFET   (ii) When and  

13. Operation of JFET   (iii) When and    

14. Operation of JFET   (iii) When and  

15. Operation of JFET   (iv) When is negative and  

16. Operation of JFET  

17. Characteristics of JFET   Output or Drain Characteristics relationship between drain current and drain to source voltage for different values of gate-to-source voltage Transfer Characteristics relationship between drain current and gate-to-source voltage for different values drain-to-source voltage  

18. Characteristics of JFET  

19. Drain Characteristics of JFET  

20. Drain Characteristics of JFET   Ohmic Region  

21. Drain Characteristics of JFET   Active Region

22. Drain Characteristics of JFET   Breakdown Region

23. Transfer Characteristics of JFET  

24. Characteristics of JFET  

25. JFET Parameters Main parameters of a JFET when connected in common-source AC Drain Resistance   Transconductance   Amplification Factor   DC Drain Resistance   Power Dissipation  

26. JFET Parameters Main parameters of a JFET when connected in common-source AC Drain Resistance       It is called as dynamic drain resistance

27. Transconductance   JFET Parameters     Its unit is Siemens ( S ) or . It is also called forward transconductance ( ) or forward transadmittance  

28. Transconductance   JFET Parameters Transconductance measured at is written as     Differentiating the above equation w.r.to      

29. Transconductance   JFET Parameters When then ,        

30. Amplification Factor   JFET Parameters     Its unit is Siemens ( S ). It is also called forward transconductance ( ) or forward transadmittance  

31. DC Drain Resistance ,   JFET Parameters   It is also called the static or ohmic resistance

32. Power Dissipation   JFET Parameters Product of and  

33. MOSFET ( M etal O xide  S emiconductor  F ield E ffect  T ransistor ) is a semiconductor device A MOSFET is most commonly used in the field of Power Electronics Gate of the MOSFET is insulated from the channel by a silicon dioxide (SiO2) layer MOSFET is also called as an IGFET ( I nsulated G ate F ield E ffect T ransistor) Two basic types of MOSFETs Depletion Type – Channel exist p ermanently Enhancement Type – Channel does not exist but formed MOS FET

34. Two-Terminal MOS Structure

35. Characteristics of MOS FET Output or Drain Characteristics (O/P Current vs O/P Voltage) relationship between drain current and drain to source voltage ( Vds ) for different values of gate-to-source voltage ( Vgs ) Transfer Characteristics (O/P Current vs I /P Voltage) relationship between drain current ( ) and gate-to-source voltage ( Vgs ) for different values drain-to-source voltage ( Vds )  

36. Enhancement MOSFET (E-MOSFET)          

37. Enhancement MOSFET (E-MOSFET)

38. Enhancement MOSFET (E-MOSFET) Induced channel ( Vgs > Vth)

39. Drain Characteristics for Enhancement Type MOSFET

40. Transfer Characteristics for Enhancement Type MOSFET

41. Characteristics for Enhancement Type MOSFET

42. E-MOSFET Schematic Symbol   Conventional Circuit Symbol Circuit Symbol Simplified Circuit Symbol

43. E-MOSFET Schematic Symbol   Conventional Circuit Symbol Circuit Symbol Simplified Circuit Symbol

44. Depletion Type MOSFET    

45. Operated on two different modes Depletion Mode Enhancement Mode This type of MOSFET is also known as depletion-enhancement type MOSFET Operation of Depletion Type MOSFET

46. Operation of Depletion Type MOSFET Depletion Mode  

47. Operation of Depletion Type MOSFET Enhancement Mode

48. Transfer Characteristic of Depletion Type MOSFET

49. D-MOSFET Schematic Symbols    

50. IGBT IGBT ( I nsulated- G ate B ipolar T ransistor) Three-terminal semiconductor switching device Combines features from both the MOSFET and the BJT Used for high-voltage and high-current switching applications

51. Eq uivalent Circuit - IGBT

52. Operation of IGBT

53. Operation of IGBT    

54. Other Names for IGBT Metal Oxide Insulted Gate Transistor (MOSIGT) Insulated Gate Transistor(IGT) Gain Modulated Field Effect Transistor (GEMFET) Conductively Modulated Field Effect Transistor (COMFET)

55. Advantages of IGBT High input impedance Low ON state power loss

56. FET Circuit Configurations Common Source Common Gate Common Drain

57. Common Source Configuration

58. Common Source Configuration      

59. Common Source Configuration DC Load Line Input Voltage                        

60. Common Source Configuration DC Load Line Input Voltage                  

61. Common Source Configuration DC Load Line Input Voltage                  

62. Common Source Configuration DC Load Line   Drain-to-Source Loop   When      

63. Common Source Configuration DC Load Line Drain-to-Source Loop When        

64. Common Source Configuration DC Load Line

65. Common Gate Configuration

66. Common Gate Configuration Analyzing Gate-to-Source loop         Substitute        

67. Common Gate Configuration Determining the Q-point for CG Configuration

68. Common Gate Configuration Finding Output Voltage             Voltage drop between Drain-to-source   Voltage at Drain  

69. Common Gate Configuration Finding Output Voltage           Voltage drop between Drain-to-source   Voltage at Drain        

70. Common Drain Configuration

71. Common Drain Configuration   Output Voltage   Input Voltage      

72. CMOS

73. CMOS

74. CMOS Inverter

75. CMOS Inverter Logic 0 – 0V Logic 1 – 5V

76. CMOS Inverter Source to Drain

77. CMOS Inverter Source to Drain Drain to Source

78. CMOS Inverter Source to Drain Drain to Source Logic Level PMOS NMOS Output SC OC 1 OC SC Logic Level PMOS NMOS SC OC 1 OC SC Truth Table