BJT vs FET ( JFET, MOSFET )

                  _____BJT - Bipolar Junction Transistor_____                                                    

   

   

  

Three terminal active electronics device

  Used for amplification and switching








Important Points 

• The current flow through the transistor occurs due to holes and electrons 
• John Bardeen, William Shockley, and Walter Brattain are the inventors of  transistor
• In 1956 they won Nobel prize for the invention
• The first transistor radio was made in 1954 ( Regency TR1 )  

     Doping

             
      The process of adding controlled amount of impurities to a semiconductor is called doping     

• The 3 terminals are named Collector, Emitter, and Base
• Emitter    :-     Heavily doped
• Collector :-     Medium doped
• Base        :-     Lightly doped 

     Configuarions 

1. Common Base                -  Used as constant current source
2. Common Collector         -  Voltage follower ( buffer )
3. Common Emitter            -  Voltage and power amplifier

           

            Parameter                       CB                        CE                 CC

• Input impedance              Very low               Low               Very high
• Output impedance           Very high              Medium          Very low
• Current gain                    Less than 1           High               Higher than CE
• Voltage gain                     High                    High               Less than 1
• Leakage current               Very small            Very high         Very high

     Operating regions

 

1. Cut off region    -   Both input and output are reverse biased
2. Active region  -  Normal region of operation, input forward and output reverse biased
3. Saturation region - Both input and output are forward biased

_____FET - Field Effect Transistor_____ 

    Classisfication

1. JFET
2. MOSFET

    JFET - Junction Field Effect Transistor 

    Classification

1. N - type
2. P - type

    MOSFET- Metal Oxide Semiconductor FET

   Classification

1. Enhancement type
2. Depletion type

BJT vs FET

                        BJT                                       FET

• Biploar                                                Unipolar
• Current controlled                              Voltage controlled
• Less input impedance                         High input impedance
• More noise                                          Less noise
• Difficult to fabricate                           Easy to fabricate
• High gain-bandwidth product             Small gain-bandwidth product