Q.Mention the disadvantages of positive feedback.

Because positive feedback aids the input, it raises the gain but degrades every other quality of the amplifier, which is why amplifiers avoid it. …

[!TLDR]

Positive feedback increases distortion and drift, makes the gain unstable and the frequency response poor, and tends to push the amplifier into oscillation.

In positive feedback the sampled output is returned in phase, so $V_i = V_s + V_f$ and the net input grows. This raises the gain but harms the amplifier in every other respect:

• More distortion — the in-phase feedback reinforces internally generated distortion rather than cancelling it.
• Poor gain stability — any change in device parameters is magnified, so the gain will not stay constant.
• Poor frequency response — the effective bandwidth is reduced.
• More drift — the operating point wanders more with temperature and time. …