| 摘要 |
PURPOSE:To select automatically a color subcarrier frequency by a device with simple constitution by switching the reference frequency of a chrominance subcarrier by an output of an oscillator which can be constituted to a flip-flop, and stopping an oscillation of the oscillator by a demodulating color signal. CONSTITUTION:A chrominance subcarrier oscillator 33 is switched to 3.58MHz for a standard NTSC system and 4.43MHz for a pseudo NTSC system by switching connected crystals 20, 21 by switches 19a, 19b. When a color signal component is not obtained, an output of a color erasing circuit 17 becomes high potential and an FET45 becomes off, therefore, an oscillation consisting of invertors 41, 42, resistance 44 and a capacitor 43 is executed, and the switches 19a, 19b are turned on alternately. As a result, the reference frequency of an oscillator 33 is switched, and when the color signal component is obtained and the FET45 becomes on, the invertors 41, 42 become a flip-flop, and the reference frequency is fixed. |
