Monday, 17 February 2020

Field-Effect Transistor- Symbol, Types, Classification, Advantages, Disadvantages, applications.

Field-Effect Transistor(FET)


  • The basic principle of the field-effect transistor (FET) has been known since J. E. Lilienfeld’s patent of 1925. 
  • The theoretical description of a FET made by Shockley in 1952 proved the way for development of a classic electronic device which provides the designer the means to accomplish nearly every circuit function. 
  • At one time, the field-effect transistor was known as a “unipolar” transistor. The term refers to the fact that current is transported by carriers of one polarity (majority), whereas in the conventional bipolar transistor carriers of both polarities (majority and minority) are involved. 
  • This Application Note provides an insight into the nature of the FET, and touches briefly on its basic characteristics, terminology, parameters, and typical applications.
  • The Field Effect Transistor or FET is a electronic device. 
  • Its output impedance is high which requires for many circuits.

General Structure:
Field-Effect Transistor
Field-Effect Transistor

Typical Field Effect Transistor

  • The Field Effect Transistor is a three terminal unipolar semiconductor device that has very similar characteristics to those of their Bipolar Transistor counterparts ie, high efficiency, instant operation, robust and cheap and can be used in most electronic circuit applications to replace their equivalent bipolar junction transistors (BJT) cousins.
  • Field effect transistors can be made smaller and along with their low power consumption and power dissipation makes them ideal for use in integrated circuits such as the CMOS range of digital logic chips.
  • In FET's  there are also two basic classifications of Field Effect Transistor, called the N-channel FET and the P-channel FET.
  • The field effect transistor is a three terminal device that is constructed with no PN-junctions within the main current carrying path between the Drain and the Source terminals, which correspond in function to the Collector and the Emitter respectively of the bipolar transistor. The current path between these two terminals is called the "channel" which may be made of either a P-type or an N-type semiconductor material. 
  • The control of current flowing in this channel is achieved by varying the voltage applied to the Gate. As their name implies, Bipolar Transistors are "Bipolar" devices because they operate with both types of charge carriers, Holes and Electrons. The Field Effect Transistor on the other hand is a "Unipolar" device that depends only on the conduction of electrons (N-channel) or holes (P-channel).
  • The Field Effect Transistor has one major advantage over its standard bipolar transistor cousins, in that their input impedance, ( Rin ) is very high, (thousands of Ohms), while the BJT is comparatively low. This very high input impedance makes them very sensitive to input voltage signals, but the price of this high sensitivity also means that they can be easily damaged by static electricity. 
  • There are two main types of field effect transistor, the Junction Field Effect Transistor or JFET and the Insulated-gate Field Effect Transistor or IGFET), which is more commonly known as the standard Metal Oxide Semiconductor Field Effect Transistoror MOSFET for short.

Symbol Of FET

Symbol  Of FET
Symbol  Of FET

Types Of  FET-

There are main two types of FET are following.

1.Junction Field Effect Transistor or JFET and
2.Insulated-gate Field Effect Transistor or IGFET)

Classification Of FET

Classification Of FET

Classification Of FET

Advantages of FET

  • Current flow is majority carriers only.
  • Immune to radiation.
  • High input resistance.
  • Less noisy.
  • No offset voltages at zero drain current.
  • High thermal stability.

Disadvantages of FET

  • Smaller gain bandwidth compared to BJT.


  • In Amplifiers                                                                              
  • Switches
  • Voltage-Controlled Resistors
  • Mixers
  • Oscillators
  • Current Limiters


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