Intro_BJT_FET

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					ME 4447: Mechatronics
     Transistors

    Paxton Billingsley
      Faiza Hassan
      Hanif Hunter
      David Stone
                 Definition
• A transistor is an          C
  electronic three
  terminal device,        B
  consisting of a
  collector, base and
  emitter.                E   E
         Transistor Properties
• One-way property
• signal gain
• coupling of circuits with differing impedance
  levels
• switch (as in ME 4447)
• non-linear effects used in communication
  circuits
               Transistor Types
• Bipolar junction                 • FETS
  transistors
                                          -JFETS
  -npn
                                          -MOSFETS
  -pnp

                            Transistors


               BJTS                          FETS
                                          p-channel or
                                           n-channel


         npn          pnp     JFETS        MOSFETS       other
Bipolar Junction Transistors (BJT)
• Invented in 1948 by Bill Shockley at Bell
  Laboratories to amplify telephone signals
• First practical design to replace vacuum tubes
• Constructed as a “sandwich” of
  semiconductors doped with N-type and P-type
  impurities
            Two Types of BJT’s
• NPN BJT       C      • PNP BJT     E

     C                      E
              N-type               P-type

B                      B
        B     P-type               N-type   B


    E         N-type       C       P-type




                E
                                     C
           How They Work



• Holes flow from (1) to (2)
• Forward bias voltage controls the collector
  current
• IC is independent of VBE
    Summary of BJT Operation
• N-type: electrons are majority carriers
• P-type: holes are majority carriers
• Majority carriers always flow from emitter
  to collector
• Increasing base-emitter voltage increases
  current flow from emitter to collector
            Common Emitter



•   Emitter is common to input and output
•   Most commonly used configuration
•   Medium input and output impedance
•   High voltage gain
•   High current gain
              Common Base



• Base is common to        •   Low input impedance
  input and output         •   High output impedance
• Used in high             •   Unity current gain
  frequency applications   •   High voltage gain
          Common Collector



• More commonly known as “emitter follower”
• Used as a buffer for circuits with different
  impedences
• High input impedence, low output impedence
• Unity current gain, high voltage gain
Summary of BJT Configurations
                                                        COMMON
  CONFIGURATION      COMMON BASE   COMMON EMITTER    COLLECTOR
                                                    (Emitter Follower)
   INPUT/OUTPUT
       PHASE             0°             180°               0°
   RELATIONSHIP
   VOLTAGE GAIN         HIGH          MEDIUM              LOW

   CURRENT GAIN         LOW           MEDIUM             HIGH

    POWER GAIN          LOW            HIGH             MEDIUM

  INPUT RESISTANCE      LOW           MEDIUM             HIGH



      OUTPUT            HIGH          MEDIUM              LOW
    RESISTANCE
Field Effect Transistors
    (Paxton Billingsley)
                 History
• Invented in late 1940’s by Shockley.
• Late 1960’s manufacturing enabled
  effective use of field-effect transistors.
• Shockley never prospered in Silicon Valley.
       Field Effect Operations
• Control one electrical signal with another.
• 3 - connections, gate, source and drain.
• Transfer patterns of signal fluctuation from
  a small input signal to larger output.
     Why is it called Field Effect?
•   Because of the Field Effect!
•   Strong electrical field created .
•   This field controls a second signal.
•   The second signal mimics the gate signal
    but larger.
                   Polarity
•   2 types
•   n-channel corresponds to npn
•   p-channel corresponds to pnp
•   Behave similarly except in p-type hole not
    electrons cause the current.
                 Variety
•   2 varieties of FET
•   junction FET (JFET)
•   metal-oxide semiconductor (MOSFET)
•   similar properties
Junction FET (JFET)
       Basic JFET

                 Drain


       iG
                  +
                          iD

Gate               VDS
   +
       VGS          -
             -   Source
            JFET Terminals
• 3 Terminals
• Gate (G) this is the input signal with
  information
• Source (S) this is the source voltage
• Drain (D) this is the output
JFET Characteristics
    JFET Regions of Operation
• Ohmic Region: Behaves as a resistor. Gate
  Voltage controls level of resistance,
  starting linear then moving non-linear as VD
  increases.
• Saturation Region: Device behaves as a
  current source controlled by gate source
  voltage.
          FET Applications
• Preferred for weak-signal work, for example
  in wireless communications and broadcast
  receivers.
• Not used for high-power amplification.
• Single chip may contain many thousands of
  FETs along with other components.
Mosfet
           Power Transistors
• Used for power amplification.
• They can be BJTs and MOSFETs or any
  other type of transistor.
• Power transistor is just an application of any
  transistor
                   Uses
• Audio Amplification
• Amplification in a RF (radio frequency)
  systems
• Many more uses
                    Some points
• Common-means that that part is grounded and is not the
  input nor the output signal.
• AV is the voltage gain.
• AI is the current gain.
• AP is the power gain and the product of AV and AI.
• Whenever there is a thevinin voltage that part of the circuit
  was “thevinised”. To change back we multiply by vth/vo.
• Transconductance of BJT’s is gm. This number is constant for
  given BJT’s.
3 Types Bipolar Power Transistor
Setups or 3 ways a BJT is hooked
          up in a circuit
• Common Emitter (CE)
• Common Base (CB)
• Common Collector (CC)
Bipolar Power Transistor CE
              • AVth=-gmRL=vth/vo
              For R5 = 0, otherwise:
              • AVth=-RL/R5=vth/vo
              • AI=-o
              • AP= Avth*vin/vth* AI
Bipolar Power Transistor CC
              • AVth=1=vth/vo
              • AI=o+1
              • AP= Avth*vin/vth* AI
                   =o+1
Bipolar Power Transistor CB
             • AVth=gmRL=vth/vo
             • AI=1
             • AP= Avth*vin/vth* AI
                  =gmRL=vth/vo
 3 Types FET Power Transistor
Setups or 3 ways a FET is hooked
          up in a circuit
• Common Source (CS)
• Common Drain (CD)
• Common Gate (CG)
FET Power Transistor CS
           • AVth=gmRL=vth/vo
           For R5 = 0, otherwise:
           AVth=-RL/R5=vth/vo
           • AI= 
           • AP = 
FET Power Transistor CD
           • AVth=1=vth/vo
           • AI= 
           • AP = 
FET Power Transistor CG
           • AVth=gmRL=vth/vo
           • AI= 1
           • AP= gm *vin/vth* RL
           Power Transistors
• Used for power amplification.
• They can be BJTs and MOSFETs or any
  other type of transistor.
• Power transistor is just an application of any
  transistor
                   Uses
• Audio Amplification
• Amplification in a RF (radio frequency)
  systems
• Many more uses
                    Some points
• Common-means that that part is grounded and is not the
  input nor the output signal.
• AV is the voltage gain.
• AI is the current gain.
• AP is the power gain and the product of AV and AI.
• Whenever there is a thevinin voltage that part of the circuit
  was “thevinised”. To change back we multiply by vth/vo.
• Transconductance of BJT’s is gm. This number is constant for
  given BJT’s.
3 Types Bipolar Power Transistor
Setups or 3 ways a BJT is hooked
          up in a circuit
• Common Emitter (CE)
• Common Base (CB)
• Common Collector (CC)
Bipolar Power Transistor CE
              • AVth=-gmRL=vth/vo
              For R5 = 0, otherwise:
              • AVth=-RL/R5=vth/vo
              • AI=-o
              • AP= Avth*vin/vth* AI
Bipolar Power Transistor CC
              • AVth=1=vth/vo
              • AI=o+1
              • AP= Avth*vin/vth* AI
                   =o+1
Bipolar Power Transistor CB
             • AVth=gmRL=vth/vo
             • AI=1
             • AP= Avth*vin/vth* AI
                  =gmRL=vth/vo
 3 Types FET Power Transistor
Setups or 3 ways a FET is hooked
          up in a circuit
• Common Source (CS)
• Common Drain (CD)
• Common Gate (CG)
FET Power Transistor CS
           • AVth=gmRL=vth/vo
           For R5 = 0, otherwise:
           AVth=-RL/R5=vth/vo
           • AI= 
           • AP = 
FET Power Transistor CD
           • AVth=1=vth/vo
           • AI= 
           • AP = 
FET Power Transistor CG
           • AVth=gmRL=vth/vo
           • AI= 1
           • AP= gm *vin/vth* RL
             Conclusion
Most common applications of transistors:
•switch
•amplifier
QUESTIONS

				
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posted:4/9/2011
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