| 摘要 |
PURPOSE:To operate a entitled device stably and precisely by dividing an output of a chrominance subcarrier generator so as to be used as a standard signal and comparing the frequency between the standard signal and a switching control signal. CONSTITUTION:A standard signal formed by dividing it from a chrominance subcarrier is inputted to a terminal (a) of a frequency comparator 11. When the frequency of an output of an AM detector 2 is higher than that of the standard signal, the output of a terminal (c) is ''1'' and the output of a terminal (d) is ''0''. When a signal with the frequency lower than that of the standard signal is inputted to a terminal (b), the output of the terminal (c) is ''0'' and the output of the terminal (d) is ''1''. Thus, AND gates 8, 9 generate outputs only at the output of a stereophonic signal and a double signal, enabling to discriminate the switching control signal. Thus, stable and precise operation can be performed and IC configulation can be easily formed, saving electric power. |
