Device 2

• Transistor


  A three terminal device in which its operation depends on the interaction between majority and minority carriers
• Transistor


  • Consists of the base, collector and emitter
  • Also called Bipolar Junction Transistor (BJT)
• Bipolar Junction Transistor (BJT)


  Its operation is based on two types of charged carriers (the majority and minority) meaning 2 junctions
• Transistors


  • Active devices that can act as a switch or an amplifier in electronic devices
• Three regions of transistor operation

  • Active region
  • Saturation region
  • Cut-off region
• Active region


  Transistor operates as an amplifier where Ic=BIB
• Saturation region


  Transistor is fully on and operates as a switch where Ic=0 (no current flows)
• Cut-off region


  Transistor acts as an insulator where Ic=0
• Transistor operation


  1. Emitter-base junction is forward-biased

  2. Collector-base junction is reverse-biased
• Emitter current


  Consists of majority carrier current (Ie) and minority carrier current (Ico)
• Transport factor


  Ratio of injected carrier current reaching the junction to injected carrier current at emitter junction
• Large signal current gain

  Ratio of the collector current increment to the base current increment
• Semiconductors can be classified as extrinsic and intrinsic
• Difference between conductors, insulators and semiconductors is based on their band structure
• 1. channel JFET


  Operation depends on varying the gate-source voltage (Vgs) and drain-source voltage (Vds)
• 1. channel JFET


  • Has two main characteristics: transfer characteristics and drain characteristics
• Three ways to configure a bipolar transistor

  • Common collector (CC)
  • Common emitter (CE)
  • Common base (CB)
• Common base (CB) configuration


  Has high current gain and no voltage gain
• Majority carriers in CB configuration

  Cross the reverse-biased junction because the injected majority carriers can appear as minority carriers in the N-type materials
• Three regions of output characteristics in CB configuration

  • Active region
  • Saturation region
  • Cut-off region
• Active region in CB configuration

  Collector current equals the emitter current
• Saturation region in CB configuration

  Both base-emitter and collector-base junctions are forward biased
• Cut-off region in CB configuration

  Base-emitter and collector-base junctions are reverse biased, transistor acts as a switch
• Alpha (α)


  Ratio of collector current to emitter current in DC mode
• Field Effect Transistor (FET)


  Voltage operated semiconductor device, acts as both amplifier and switch
• Types of FETs


  • Junction Field Effect Transistor (JFET)
  • Metal Oxide Semiconductor Field Effect Transistor (MOSFET)
• JFET


  Voltage driven device, operates based on the variation of gate-source voltage (Vgs) and drain-source voltage (Vds)
• Regions of JFET operation

  • Ohmic region
  • Saturation region
  • Breakdown region
• Ohmic region in JFET

  JFET behaves like an ordinary resistor, drain current increases linearly with drain-source voltage
• Saturation region in JFET

  Drain current increases slowly with increase in drain-source voltage due to reduction in effective channel width
• Pinch-off voltage (Vp)


  Vds at which the channel width reduces to minimum value
• MOSFET


  Has an insulated gate, very high input resistance compared to BJT
• Types of MOSFETs


  • Enhancement mode MOSFET
  • Depletion mode MOSFET
• Enhancement mode MOSFET


  Can only be operated in enhancement mode
• Depletion mode MOSFET


  Can be operated in both depletion mode and enhancement mode
• Drain current in E-MOSFET

  ID = IDSS (1 - Vgs/Vp)^2 when Vgs is positive
• Drain current in D-MOSFET

  ID = IDSS when Vgs = 0, ID = IDSS (1 - Vgs/Vp)^2 when Vgs is positive
• Ohmic region


  The linear region of operation for a JFET where it acts like a voltage-controlled resistor and the current flowing through the device is directly proportional to the voltage applied to the gate terminal.
• Saturation region


  The active region of operation for a JFET where it acts like a current source and the current flowing through the device is relatively constant, regardless of the voltage applied to the drain terminal.
• A JFET consists of two back-to-back connected pn junctions with one end open and the other end closed by a metal contact called the gate.