Plan: Analog electronics

Field-effect transistor

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  The field effect transistor, FET is a key electronic component using within many areas of the electronics industry.
  
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  The FET used in many circuits constructed from discrete electronic components in areas from RF technology to power control and electronic switching to general amplification.
  
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  However the major use for the field effect transistor, FET is within integrated circuits. In this application FET circuits consume much lower levels of power than ICs using bipolar transistor technology. This enables the very large scale integrated circuits to operate. If bipolar technology was used the power consumption would be orders of magnitude greater and the power generated far too large to dissipate from the integrated circuit.
  
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  Apart from being used in integrated circuits, discrete versions of these semiconductor devices are available both as leaded electronic components and also as surface mount devices.
  

Bipolar transistor
If we now join together two individual signal diodes back-to-back, this will give us two PN-junctions connected together in series which would share a common Positve, (P) or Negative, (N) terminal. The fusion of these two diodes produces a three layer, two junction, three terminal device forming the basis of a Bipolar Junction Transistor, or BJT for short.
Transistors are three terminal active devices made from different semiconductor materials that can act as either an insulator or a conductor by the application of a small signal voltage. The transistor’s ability to change between these two states enables it to have two basic functions: “switching” (digital electronics) or “amplification” (analogue electronics). Then bipolar transistors have the ability to operate within three different regions:

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  The flow of charge in a Bipolar transistor is due to the diffusion of charge carriers between the two regions belonging to different charge concentrations. Regions of BJT are known as the base, collector, and emitter.
  
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  The emitter region is highly doped when compared to other layers. Both collector and base layers have the same charge carrier concentrations. Among these junctions, the base-emitter junction is forward biased, and the base-collector junction is reverse biased. Forward biased means p-doped region has more potential than the n-doped side.