| 摘要 |
PURPOSE:To receive TV signals of the B/PAL and M/NTS systems with simple circuit constitution, by switching horizontal frequencies of a horizontal oscillating circuit by a detection signal obtained by detecting output amplitude variations of a vertical oscillating circuit due to a difference in field frequency. CONSTITUTION:To a vertical oscillating circuit 1, the 1st and 2nd different vertical synchronizing signals for B/PAL system reception and M/NTSC system reception are inputted, and the 1st and 2nd saw-tooth waves which correspond to those synchronizing signals are outputted. The peak value of each saw-tooth wave is rectified by a peak rectifying circuit 2, whose peak rectification output is applied to a Zener diode 3. This diode 3 turns on when the rectification output exceeds some constant voltage, and the output of the diode 3 is inputted to a switch circuit 4, which outputs a signal different in level. This different level is inputted to a horizontal oscillating circuit inputting a horizontal synchronizing signal to switch horizontal oscillation frequencies automatically, thus receiving TV signals of the B/PAL and M/NTSC systems. |
