FET ( Field Effect Transistor)

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FET ( Field Effect Transistor). Few important advantages of FET over conventional Transistors. Unipolar device i. e. operation depends on only one type of charge carriers ( holes or electrons) Voltage controlled Device (gate voltage controls drain current) - PowerPoint PPT Presentation

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  • FET ( Field Effect Transistor)Unipolar device i. e. operation depends on only one type of charge carriers (holes or electrons) Voltage controlled Device (gate voltage controls drain current)Very high input impedance (109-1012 )Source and drain are interchangeable in most Low-frequency applicationsLow Voltage Low Current Operation is possible (Low-power consumption)Less Noisy as Compared to BJTNo minority carrier storage (Turn off is faster) Self limiting deviceVery small in size, occupies very small space in ICsLow voltage low current operation is possible in MOSFETS Zero temperature drift of out put is possible.Few important advantages of FET over conventional Transistors

  • JFETMOSFET (IGFET)n-Channel JFETp-Channel JFETTypes of Field Effect Transistors (Classifications) n-Channel EMOSFET p-Channel EMOSFET Enhancement MOSFETDepletion MOSFETn-Channel DMOSFET p-Channel DMOSFET FET

  • Figure: n-Channel JFET.The Junction Field Effect Transistor (JFET)

  • JFET SYMBOLSn-channel JFETn-channel JFET(Offset-gate symbol)p-channel JFET

  • Figure: n-Channel JFET and Biasing Circuit.Biasing the JFET

  • Figure: The nonconductive depletion region becomes broader with increased reverse bias. (Note: The two gate regions of each FET are connected to each other.)Operation of JFET at Various Gate Bias Potentials

  • PP+-DC Voltage Source+-+-NNOperation of a JFETGateDrainSource

  • Figure: n-Channel FET for vGS = 0.Simple Operation and Break down of n-Channel JFET

  • Figure: If vDG exceeds the breakdown voltage VB, drain current increases rapidly.Break Down RegionN-Channel JFET Characteristics and Breakdown

  • Figure: Transfer (or Mutual) Characteristics of n-Channel JFETIDSSVGS (off)=VPTransfer (Mutual) Characteristics of n-Channel JFET

  • Biasing Circuits used for JFETFixed bias circuitSelf bias circuitPotential Divider bias circuit

  • JFET (n-channel) Biasing CircuitsFor Self Bias CircuitFor Fixed Bias CircuitApplying KVL to gate circuit we getandWhere, Vp=VGS-off & IDSS is Short ckt. IDS

  • JFET Biasing Circuits Countor Fixed Bias Ckt.

  • JFET Self (or Source) Bias Circuit

  • The Potential (Voltage) Divider Bias

  • A Simple CS Amplifier and Variation in IDS with Vgs

  • FET Amplifier Configurations and Relationships:Note: The biasing circuit is the same for each amp.