| 摘要 |
PURPOSE:To use only one filter to facilitate the formation of a digital IC circuit, and to easily modify the characteristic through the modification of a reference value for comparators by deciding the level of the envelope amplitude of an input signal by means of the two comparators. CONSTITUTION:The input to a control means 106 is an FM-modulated video signal M; an envelope detector 107 comprises an amplitude detector 108 and the filter 109 that eliminates unnecessary components and outputs the envelope amplitude A of the signal M. The comparator 110 compares the envelope amplitude A with a first reference value R1, and outputs a decision result C1, while the comparator 111 compares the amplitude A with a second reference value R2(R2<R1) and outputs a decision result C2. The signals C1, C2 are inputted to a control signal generator 112, and the generator 112 output a control signal S so that a switch 104 selects an input terminal 104b.
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