| 摘要 |
<p>A synchronizing signal producing system for a television device comprises a first counter for receiving input clock pulses having a frequency of an integral multiple of a horizontal synchronizing signal to generate output pulses having a vertical synchronizing frequency with a larger width than that of the clock pulse; a second counter for counting the clock pulses in synchronization with the arrival of a vertical synchronizing signal from the outside; a comparison pulse generator coupled with the second counter so as to derive a clock pulse counted, by the second counter, at a time corresponding to substantially the center of the width of the output pulse from the first counter; a phase comparator for comparing the phase of the output pulse from the comparison pulse generator with that of the output pulse from the first counter; and an output switching circuit for deriving as a vertical synchronizing output for the television device the output pulse of the first counter when the output pulse from the first counter and that from the comparison pulse generator are evaluated by the comparator to be in phase and the output pulse associated synchronously with the vertical synchronizing signal obtained from the outside through the second counter when they are evaluated by the comparator to be out of phase, whereby the television device can be driven always in substantially synchronized condition not only in a case where the vertical synchronizing signal from the outside is equal in frequency to a standard vertical synchronizing signal, but also in a case where the received vertical synchronizing signal is somewhat different in frequency from the standard vertical synchronizing signal.</p> |
