门限 is the 用 of an 电子 电路 or 软件 相当于 which determines the opening and closing of the 扩 of an 输入 信号 allowing 信号 to persist only above a user-defined 阀值 The 相反 of 门限 is known as 反门限 which 允许 only the 信号 below the user-defined 阀值