• Twin-T is basically a frequency selective network. The amplitude and response of a twin –T network shows that the phase shift introduced by this network is zero at particular frequency.

• The Twin-T network acts as the phase lead-lag network. It introduces a phase shift that varies between +90 to -90 degrees.

• The circuit diagram for Twin-T oscillator is as shown in the above figure .It consists of an OP-AMP operating as non-inverting amplifier i.e introducing 0 phase shift.

• The resistor R1 and R2 introduce a positive feedback. The Twin-T network introduces 0 phase shift and its output voltage is minimum at f = ft. Therefore only at this frequency the positive feedback in the amplifier becomes effective and oscillations are obtained the frequency of oscillation is given by

                        F= 1/2πRC

• The oscillator frequency cannot be varied. It is a single frequency oscillator.

• The variable resistance R2 in the OP-AMP circuit adjust the positive feedback and the variable resistance R/2 in the Twin –T network ensures that the oscillations take place at f = fr

• This oscillator provides good stability of signal.

• This oscillator is very rarely used as it operates at signal frequency.