Introduction

We know that earlier electronic devices were made up of vacuum tubes or valves

Vacuum tubes or Valves:

• The evolution of vacuum tubes started with diode and proceeded to triode, tetrode and pentode
• Valves control the flow of electrons; In diodes, there were two electrodes – cathode and anode
• Similarly, triode had three electrodes – cathode, grid and anode; tetrode had four electrodes – anode, two grids and cathode; pentode had five electrodes –anode, three grids and cathode
• Generally in vacuum tubes, the electrons are produced by heating the cathode using low tension battery; The vacuum helps in electron not losing its energy by collision with air molecules in the way
• However, the vacuum tube devices had some disadvantages and they are
  • Bulky
  • Operate at high voltages
  • Consume more power
  • Have limited life
  • Low reliability

  Diodes and transistors

• Next came the discovery of semiconductor junction, namely, junction diode and transistors
• These replaced the vacuum tubes or valves

• The advantages of semiconductor devices are
  • Small in size
  • Operate at low voltages
  • Consume small power
  • Long life
  • High reliability
• Though the above advantages are present, the circuits consisting of transistors were still bulky, less shock proof
• Hence, it led to the discovery of integrated circuits which is a major revolution in the electronic industry

Example – The earlier generation television and computer monitors were very bulky as they were based on the principle of vacuum tubes; now days, we have LCD (Liquid Crystal Display) monitors which support solid state electronics