In order to ensure that the logic circuit can work normally, the level value representing the logic state of the circuit must fall within a certain range. For example, for 3.3V logic, a high level greater than 2V is a logic 1, and a low level less than 0.8V is a logic 0. When the input level of the logic gate circuit is within the above range, the circuit can ensure the correct judgment of the input logic state. When the level value is between 0.8V and 2V, the correct judgment of the input logic state cannot be guaranteed. For the NOT gate in this example, its output may be logic 0, logic 1, or in an indeterminate state. . Therefore, when the input level is outside the specified range, a logic error may occur.