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Transistor as an oscillator




Transistor as an oscillator

  • electronic oscillator is a circuit which converts DC energy with AC energy at very high frequency
  • Oscillators generates alternating voltage when it is supplied energy from a DC source
  • Figure below shows the representation of an oscillator and the basic parts of this circuit are
    (a) An amplifier circuit
    (b) An LC network

    Transistor as an oscillator
  • Amplifier circuit is just a transistor used in CE mode and the LC network consist of a inductor and capacitor

  • The resonance frequency of this circuit determines the frequency at which oscillator will oscillates and it is
    $f_0= \frac {1}{2 \pi \sqrt {LC}}$
  • In this circuit only batteries are used to bias the transistor and no other external signal is applied to the amplifier circuit
  • The LC network is used as a feedback to fed a part of the output signal back to the input section
  • This signal is again amplified by amplifier section and a part is again feedback to the input section and this makes it is a self sustained device
  • Two important and necessary conduction for circuit oscillations are (i) The feedback must be positive
    (ii) Feedback factor must be unity i.e βA=1
  • The circuit resonates at resonating frequency f0 and the output of the circuit acts a source of alternating voltage of this frequency

  • This frequency can be charged by changing L or C

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