Barkhausen criterion and various types of oscillators

The condition for sustained oscillations in a single valve self excited oscillator worked out by the German scientist Barkhausen is this that the voltage multiplication of the amplifier must exactly counterbalance the voltage dividing of the feedback circuit.

                                                β=1/A                                  

 

  

 Where, β=feedback factor, A= voltage gain

Various types of oscillators

Various types of oscillator have been designed to meet the requirement of different types of electronic equipments which are follows:

Tuned collector oscillator

Hartley oscillator

Colpitt’s oscillator

      Clapp oscillator

      Crystal oscillator

      Phase shift R-C oscillator

      Multi vibrator

      Wein bridge oscillator

      Neon lamp oscillator

      Master oscillator power amplifier

      Beat frequency oscillator    

TUNED COLLECTOR OSCILLATOR :

It is simplest type of oscillator circuit. It consists of two coils L1 and L2 wound like a transformer. Coil L1 is the connected in the collector circuit and coil L2 in the base circuit. The frequency of oscillations depends of oscillations depends on the values of L1 and C1 capacitor C provides a low reactance path to the oscillations.

When the switch S is put to ON, the collector current starts increasing and charges the capacitor C1. When this capacitor gets fully charged, it starts to discharge through L1 and the circuit begins to oscillate. These oscillations include some voltage in the coil L2 which is applied between the base and emitter of the transistor and the same appears in the amplified form in the collector circuit. The output can be obtained from the collector circuit trough a capacitor C2.

          The oscillatory frequency of the circuit is calculated by using the formula 

 There exists a ‘tuned base oscillator ‘circuit also which is based on a CB circuit.