| 摘要 |
PURPOSE:To readily judge whether an input signal crosses a reference voltage or not, by a method wherein the output of the first comparator to which the input signal and the reference voltage are applied respectively is smoothed in a rectifying circuit and supplied to the second comparator thereafter. CONSTITUTION:When an AC input signal Vi crosses a reference voltage Vr, the output of a comparator 2 becomes a rectangular wave signal, which is supplied, as a DC signal, to one input terminal of a comparator 7 through a capacitor 4, a diode 5, a capacitor 8 and the like. In this case, the reference voltage Vr is previously set so as to be lower than the level of said DC signal. Accordingly, when said DC signal is supplied to said input terminal of the comparator 7, the output thereof is of low level (or high level). By such a constitution, when the input signal Vi crosses the reference voltage Vr, a low or high level signal is outputted from the comparator. Thereby, it is possible to readily judge whether the input signal Vi crosses the reference voltage Vr or not. |
