positive feedback (PFB)
The principle of feedback distinguishes between in- phase feedback, which is the positive feedback, and out-of-phase feedback, which is the negative feedback.
In positive feedback, the feedback signal is added to the original input signal. The sum of the input signal and the feedback signal, which both have the same phase but different amplitude, form the signal effective at the input. The amplitude of the feedback signal is reduced by the feedback factor (k).