| 摘要 |
PURPOSE:To discriminate TV signal systems by a simple configuration by discriminating a TV signal system from the dividing condition of a variable dividing means switching the TV signal system to the dividing ratio corresponding to plural TV signal systems. CONSTITUTION:A TV signal of an NTSC or a PAL/SEC system is inputted to a synchronizing signal separation circuit 2 and a synchronizing signal E is separated. A pulse signal F having the frequency twice that of a horizontal synchronizing signal is formed from the synchronizing signal E by PLL 3. The signal E is inputted to a 2-stage shift register 4 and a signal I corresponding to the vertical synchronizing signal is obtained from the 1st and 2nd stage output signals G, H. When a signal belonging to the NTSC system is inputted to a terminal 1, a selector 10 selects and AND gate to decode 524, so that the output from a NAND gate is turned to ''0'', an AND gate stops the signal I and turns its output to ''0'' and a FF13 does not change its status. A counter 7 holds the dividing of 525. When a signal belonging to the PAL system is inputted, the same operation is also performed. |
