Q. Why negative feedback is employed in Wein Bridge Oscillator. Also explain the working of oscillator?

The Wein Bridge Oscillator consists of two stages of the RC coupled amplifier and a feedback network. The block diagram given in figure explain the principle of working of this oscillator. Here the two blocks are A₁ and A₂. These two represents two amplifier stages. The output of the second stage goes to the feedback network. The voltage across the parallel combination C₂R₂ is fed to the input of the first stage. First amplifier stages produce 1800 phase shift and the second amplifier also provides 180⁰ phase shift. Total phase shift is 360⁰ Therefore it is evident that for the oscillation to be maintained, the phase shift through the coupling network must be zero. It can be shown that this condition occurs at a frequency given by