| 摘要 |
PURPOSE:To detect vertical synchronizing signal frequencies of different television systems stably and without adjustment, by providing a circuit which detect two kinds of vertical frequency, and a circuit which hold them. CONSTITUTION:An input vertical synchronizing signal is inputted to a vertical synchronizing pulse generating circuit 2 through a masking circuit 1 to output a vertical synchronizing pulse. This pulse resets a 9-bit binary counter 3, to which a horizontal synchronizing signal is inputted, to start counting the horizontal synchronizing signal. Three horizontal synchronizing signal detecting circuits 4, 5, and 6 which detect the number of horizontal synchronizing signals are provided in the output side of this counter; and when respective horizontal synchronizing pulses are detected by these circuits 4, 5, and 6, and these pulses are held by holding circuits 7, 8, and 9. Outputs of holding circuits 7, 8, and 9 are inputted to 50Hz and 60Hz vertical frequency detecting circuits 10 and 11 consisting of AND gates and are held in a holding circuit 12. |
