| 摘要 |
PURPOSE:To discriminate even and odd number of fields without adjustment independently of separating characteristics of a vertical synchronizing signal separation circuit, by counting the number of equivalent pulse included in one horizontal period of a PAL synchronizing signal. CONSTITUTION:A vertical synchronizing signal separation circuit 10 integrates a synchronizing signal 5 and outputs a vertical synchronizing signal 6. A wave shaping circuit 11 detects the falling of the signal 5 and outputs a shaped synchronizing signal 15. The pulse width from a monostable multivibrator 12 inhibited with retrigering is set larger than 1/2 horizontal period and smaller than one horizontal period and the vibrator 12 is triggered with the signal 15. A gate circuit 13 detects the logical product of output signals of the multivibrator 12 by taking the signal 15 as a gate pulse and gives the result to a digital counter 19, which is cleared at each prescribed time at a reset pulse generating circuit 14 with a reset pulse 18 delaying the signal 6 for a prescribed time, and an even/odd discriminating signal output line 9 is kept to a logical level L at the number of fields and inverted into H at the odd number of fields, allowing to discriminate the even and odd numbers. |
