Phase Shift and Feedback

Author: Leonard Krugman

One effect of the reactive components is to cause a phase shift between the input and output terminals. Phase shift reduces the in-phase component of the positive feedback signal. This is illustrated in Fig. 6-13 (A) where E_F is the feedback signal and φ

Fig. 6-13. (A) Effect of phase shift on feedback signal.

is the phase angle between the input and output signals. E_F1 represents the feedback amplitude at low frequencies when the reactive effects are negligible. As tke operating frequency is increased, E_F2 and the input signal are no longer in phase. Thus, only the in-phase component of E_F is useful for maintaining circuit oscillation. When the phase angle becomes so large that the in-phase component is less than the critical minimum required value, oscillation stops.