The Basic Condition of a Feedback Loop

The two Not gates controlled by outside signals and connected in series into a closed circuit is defined as feedback loop and the feedback loop whose inside and outside signals are input in the forms of NAND (NOR) gates as NAND (NCR) loop. Taking NAND loop as an example, this paper expounds the steady state and unsteady state of a feedback loop, and their conditions, and distinguish the method in theory.