SIGMA INSTITUTE OF ENGINEERING DEPARTMENT OF ELECTRICAL ENGINEERING ACTIVE LEARNING ASSIGNMENT TOPIC ON: PREPARED BY; BHAGYASHRI SHRIVASTAV( ) YUVRAJ SINH SINDHA( ) STEFEE SIROYA( ) GUIEDED BY; NIRAV PARMAR ASST.PROF.

FET & MOSFET AMPLIFIER  WHAT IS FET?  ADVANTAGES OF FET  TYPES OF FET  JFET CONSTRUCTION  N CHANNEL JFET  P CHANNEL JFET  MOSFET  D MOSFET  E MOSFET  SUMMARY TABLE

WHAT IS FET? FET IS UNI-POLAR DEVICE I.E. OPERATION DEPENDS ON ONLY ONE TYPE OF CHARGE CARRIERS (H OR E). IT IS A VOLTAGE CONTROLLED DEVICE (GATE VOLTAGE CONTROLS DRAIN CURRENT) 3

1.VERY HIGH INPUT IMPEDANCE (   ) 2.SOURCE AND DRAIN ARE INTERCHANGEABLE 3.LOW VOLTAGE LOW CURRENT OPERATION IS POSSIBLE (LOW-POWER CONSUMPTION) 4.LESS NOISY 5.NO MINORITY CARRIER STORAGE (TURN OFF IS FASTER) 6.VERY SMALL IN SIZE, OCCUPIES VERY SMALL SPACE IN ICS 4 ADVANTAGES OF FET

CURRENT CONTROLLED VS VOLTAGE CONTROLLED DEVICES 5

TYPES OF FIELD EFFECT TRANSISTORS (THE CLASSIFICATION) JFET MOSFET (IGFET) 6 n-Channel JFET p-Channel JFET n-Channel EMOSFET p-Channel EMOSFET Enhancement MOSFET Depletion MOSFET n-Channel DMOSFET p-Channel DMOSFET FET »JFET FET »JFET FET

JFET CONSTRUCTION 7 There are two types of JFET’s: n-channel and p-channel. The n-channel is more widely used. There are three terminals: Drain (D) and Source (S) are connected to n-channel,Gate (G) is connected to the p-type material

N-CHANNEL JFET OPERATION 8 The nonconductive depletion region becomes thicker with increased reverse bias. (Note: The two gate regions of each FET are connected to each other.)

9 Gate Drain Source SYMBOLS n-channel JFET Gate Drain Source p-channel JFET

10 CHARATERISTICS At the pinch-off point: any further increase in V GS does not produce any increase in I D. V GS at pinch-off is denoted as Vp. ID is at saturation or maximum. It is referred to as I DSS.

ID  IDSS 11 As V GS becomes more negative: the JFET will pinch-off at a lower voltage (Vp). I D decreases (I D < I DSS ) even though V DS is increased. Eventually I D will reach 0A. V GS at this point is called Vp or V GS(off). Also note that at high levels of V DS the JFET reaches a breakdown situation. I D will increases uncontrollably if V DS > V DSmax.

12 p-Channel JFET p-Channel JFET operates in a similar manner as the n-channel JFET except the voltage polarities and current directions are reversed

13 P-Channel JFET Characteristics As VGS increases more positively the depletion zone increases I D decreases (I D < I DSS ) eventually I D = 0A Also note that at high levels of VDS the JFET reaches a breakdown situation. ID increases uncontrollably if V DS > V DSmax.

14 There are two types of MOSFET’s: Depletion mode MOSFET (D-MOSFET) Operates in Depletion mode the same way as a JFET when VGS  0 Operates in Enhancement mode like E-MOSFET when VGS > 0 Enhancement Mode MOSFET (E-MOSFET) Operates in Enhancement mode IDSS = 0 until VGS > VT (threshold voltage) MOSFET (Metal Oxide Semiconductor FET)

15 Depletion Mode MOSFET Construction The Drain (D) and Source (S) leads connect to the to n-doped regions These N-doped regions are connected via an n-channel This n-channel is connected to the Gate (G) via a thin insulating layer of SiO 2 The n-doped material lies on a p-doped substrate that may have an additional terminal connection called SS

16 D-MOSFET Symbols

17 Enhancement Mode MOSFET Construction The Drain (D) and Source (S) connect to the to n-doped regions These n-doped regions are not connected via an n-channel without an external voltage. The Gate (G) connects to the p-doped substrate via a thin insulating layer of SiO 2. The n-doped material lies on a p-doped substrate that may have an additional terminal connection called SS

18 E-MOSFET Symbols

19 Basic Operation The Enhancement mode MOSFET only operates in the enhancement mode. VGS is always positive IDSS = 0 when VGS < VT As VGS increases above VT, ID increases If VGS is kept constant and VDS is increased, then ID saturates (IDSS) The saturation level, VDSsat is reached.

20 p-Channel Enhancement Mode MOSFETs The p-channel Enhancement mode MOSFET is similar to the n-channel except that the voltage polarities and current directions are reversed.

21 Summary Table JFET D-MOSFETE-MOSFET

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